chapter xi.)

Reproduction by division is by far the most common of all forms of propagation. It is the normal form of monogony, not only in many of the protists, but also in the tissue-cells which compose the tissues of the histona. It is, moreover, the sole method of propagation for most of the monera, both chromacea and bacteria, which are in consequence often comprised under the title of "cleavage-plants" (_schizophyta_). Self-cleavage is also found among the higher multicellular organisms--namely, the cnidaria (polyps, medusæ). It usually takes the form of division into two parts (_dimidiatio_ or hemitomy), the body splitting into two equal halves. The plane of division is sometimes indefinite (fragmentary-cleavage), sometimes coincident with the long axis (length-cleavage), sometimes with the transverse axis, vertical to the long axis (transverse-cleavage), and less frequently with a diagonal axis (oblique-cleavage). When the segmentation of a cell proceeds so rapidly that the transverse-cleavage follows immediately on the length-cleavage, and the two are at length made to coincide, twofold division is changed into fourfold division. And when the process is repeated in quick succession, and the body falls at last into a number of small and equal pieces, we have manifold division (polytomy); as in the spore-formation of the sporozoa and rhizopoda, and in the embryonic sac of the phanerogams.

Asexual propagation by budding is chiefly distinguished from segmentation by the fact that the determining transgressive growth is only partial in the one and total in the other. The bud produced is, therefore, younger and smaller than the parent from which it issues; the latter may replace the lost part by regeneration and produce a number of buds simultaneously or successively without losing its individuality (whereas this is destroyed in division). Propagation by budding is rare among the protists, and more common among the histona--that is, with most of the tissue-plants and the lower, stock-forming, tissue-animals (cœlenteria and vermalia). Most stocks (cormi) are formed by a sprout or person shooting out buds which remain united to it. The layer and shoots of tissue-plants are detached buds. The two chief kinds of gemmation are terminal and lateral. Terminal budding takes place at the end of the long axis, and is not far removed from transverse division (for instance, the strobilation of the acraspedæ medusæ and the chain tape-worms). Lateral budding is much more common; it determines the branching of trees and generally of complex plants, and also of the tree-shaped stocks of sponges, cnidaria (polyps, corals), bryozoa, etc.

A third form of asexual reproduction is the formation of spores or "germ-cells," which are usually produced in great numbers inside the organism, then detached from it, and developed into new organisms without needing fertilization. The spores are sometimes motionless (rest-spores or paulospores); sometimes they have one or more lashes which enable them to swim about (rambling-spores or planospores). This monogenetic propagation is very common among the protists, both protophyta and protozoa. Among the latter the sporozoa (gregarinæ, coccidia, etc.) are remarkable for the passing away of the whole unicellular organism in the formation of spores; in this case and in many of the rhizopods (_mycetozoa_) the process coincides with manifold cell-division. In other cases (radiolaria, thalamophora) only a portion of the parental cells is used for the production of spores. Spore-formation is very common among the cryptogams; here it usually alternates with sexual propagation. The spores are generally formed in special spore-capsules (sporangia). In the flowering plants (anthophyta) sporogony has disappeared. It is found at times in the tissue-animals (in the fresh-water sponges); in this case the sporangia are called _gemmulæ_.

The essential feature of sexual generation is the coalescence of two different cells, a female ovum (egg-cell) and a male sperm-cell. The simple new cell which arises from the blending of these is the stem-cell (_cytula_), the stem-mother of all the cells that make up the tissues of the histon. But even among the unicellular protists we find in many places the beginnings of sexual differentiation; it is foreshadowed in the blending or copulation of two homogeneous cells, the gameta. We may conceive this process, or zygosis, as a peculiar and very favorable kind of growth, that is connected with a rejuvenescence of the plasm; the latter is enabled to propagate by repeated cleavage through the mixing of the two different plasma-bodies on either side (_amphimixis_). When these two gameta become unequal and differ in size and shape, the larger female body is called the macrogameton or macrogonidion, and the smaller, male part, the microgameton or microgonidion. Among the histona the first is called the egg-cell (_ovulum_), and the latter the sperm-cell (_spermium_, or _spermatozoon_). As a rule the latter is a very mobile ciliated cell, the former an inert or amœboid cell. The vibratory movements of the sperm-cells serve for approaching the ovulum in order to fertilize it.

The qualitative difference between the two copulating sexual cells (_gonocyta_), or the chemical difference between the ovoplasm of the female and the sperm-plasm of the male cell, is the first (and often the only) condition of amphigony; subsequently we find in addition (in the higher histona) a very elaborate apparatus of secondary structures. With this chemical difference is associated a peculiar double form of sensitive perception and an attraction based thereon, which is called sexual chemotaxis or erotic chemotropism. This "sex-sense" of the two gonocyta, or elective affinity of the male androplasm and the female gynoplasm, is the cause of mutual attraction and union. It is very probable that this sexual sense-function, akin to smell or taste, and the movements it stimulates, are located in the cytoplasm of the two sex-cells, while heredity is the function of the caryoplasm of the nucleus. (_Cf._ the _Anthropogeny_, chapters vi. and vii.)

The sexual difference between the two forms of gonoplasm, the ovoplasm of the female and spermoplasm of the male cell, is noticeable at the very beginning of sexual differentiation in the different sizes of the copulating gameta, and later in their increasing divergence as to shape, composition, movement, etc. It leads further to the distribution of the germinal regions (in which the sex-cells are formed) into two different individuals. When the ovum and the sperm-cell are produced in one and the same individual, we call this an hermaphrodite; and when they are formed in two different individuals (male and female), we call them monosexual, or gonochorists. In accordance with the various stages of individuality which we distinguished above (chapter vii.), we may indicate the following stages of hermaphrodism and gonochorism.

Some groups of protists, especially the highly organized ciliated infusoria (_ciliata_), are distinguished by having a separation of male and female plasm within the unicellular organism. The ciliata propagate, as a rule, in large numbers by repeated division (by indirect cell-cleavage). But this monogony has its limits, and has to be interrupted from time to time by amphigony, a rejuvenation of the plasm, which is effected by the conjugation of two different cells and the partial destruction of their nuclear matter. By conjugation is meant the partial and momentary union of two different unicellulars, while copulation is a total and permanent coalescence. When two ciliated infusoria conjugate they place themselves side by side, and connect for a time by means of a bridge of plasm. A part of the nucleus of each has already divided into two portions, one of which functions as the female standing-nucleus (_paulocaryon_) and the other as the male travelling-nucleus (_planocaryon_). The two mobile nuclei enter the plasm-bridge, and move through it, pushing against each other, into the body of the opposite cell; they then coalesce with the deeper lying standing-nucleus. When a fresh nucleus has been thus formed (by _amphimixis_) in each of the copulating cells, they again separate. The two rejuvenated cells have once more acquired the power to propagate for a long time by division.

This peculiar hermaphroditic formation of the cells, which distinguishes the ciliated infusoria and some other protists, and which we now know in its smallest details through the investigations of Richard Hertwig, Maupas, and others, is especially interesting because it proves that the chemical difference between the female gynoplasm and the male androplasm can be found within a single cell. This erotic division of labor is so important that formerly it was universally ascribed to two different cells. Recent accurate research, penetrating into the smallest visible processes of fertilization, has shown that the essential feature in the formation of a fresh individual (the stem-cell) is the blending of equal portions (hereditary parts) of the male and female nuclei; the caryoplasm of the two copulating cells is the vehicle of heredity from the parents. The cytoplasm of the cell-body, on the other hand, serves the purposes of adaptation and nutrition. As a rule the cell-body of the ovulum is very large, and is, as a food-store, very richly provided with albumin, fat, and other nutritive matter (food-yolk); while the cytoplasm of the sperm-cell is very small, and generally forms a vibrating lash, with which it moves along and seeks the ovum.

In most of the plants the female and male cells are produced by the same sprout, and in many of the lower animals by one and the same person. This kind of hermaphrodism in "individuals of the second order" is called monoclinism ("one-beddedness"). In many of the higher plants (monœcic stocks) and most of the higher animals we have diclinism ("two-beddedness")--in other words, the one sprout or person has only male, and the other sprout or person only female, organs--this is gonochorism of individuals of the second order. Monoclinism is generally associated with sedentary life (and often necessary for it), and diclinism with free movement. Adaptation to parasitic habits also favors monoclinism; thus, the crabs, for instance, are for the most part gonochoristic individuals, but the creeping crabs (_cirripedia_), which have adopted sedentary (and to an extent parasitic) habits, have become hermaphrodites in consequence. Many intestinal parasites among the lower animals (such as tape-worms, suctorial worms, wonder-snails), which live isolated lives inside other animals, have to be hermaphroditic and able to fertilise themselves if the species is to be maintained. On the other hand, many hermaphroditic flowers, although they have both sorts of sex-organs, are incapable of fertilizing themselves and have to receive this from insect visitors which carry the pollen from one flower to another.

Individuals of the third order, which we call stocks (_cormi_) in both the plant and animal worlds, also exhibit varying features in the sex-persons which compose them. When male and female diclinic sprouts or persons are found side by side on the same stock, we call this hermaphrodism of the cormi _monœcia_ ("one-housedness"); this is the case with most of the siphonophora and some of the corals. _Diœcia_ ("two-housedness") is less common: in this one stock has only male and the other only female sprouts or persons, as in poplars and osiers, most of the corals, and some of the siphonophora. The physiological advantages of crossing--the union of sex-cells of different individuals--favor progressive sex-division in the higher organisms.

A comparative study of the features of hermaphrodism and sex-division in the plant and animal worlds teaches us that both forms of sex-activity are often found in closely related organisms of one and the same group, sometimes even in different individuals of the same species. Thus, for instance, the oyster is usually gonochoristic, but sometimes hermaphroditic; and so with many other mollusks, vermalia, and articulata. Hence, the question often raised, which of the two forms of sex-division is original, is hardly susceptible of a general answer, or without relation to the stage of individuality and the place in classification of the group under discussion. It is certain that in many cases hermaphrodism represents the original feature; for instance, in most of the lower plants and many of the stationary animals (sponges, polyps, platodes, tunicates, etc.). Where we find exceptions in these groups, they are of secondary origin. It is equally certain, on the other hand, that in other cases the separation of the sexes is the primitive arrangement; as in siphonophoræ, ctenophoræ, bryozoa, cirripedia, and mollusks. In these cases the hermaphrodism is clearly secondary in the sense that the hermaphrodites descend originally from gonochorists.

It is only in a few sections of the lowest histona that the two kinds of sex-cells arise without a definite location in different parts of the simple tissue, as in a few groups of the lower algæ and in the sponges. As a rule they are formed only at definite positions and in a special layer of the tissue-body, and mostly in groups, in the shape of sexual glands (_gonades_). These bear special names in different groups of the histona. The female glands are called archegonia in the cryptogams, _nucellus_ (formed from the macrosporangia of the pteridophyta) in the phanerogams, and ovaries in the metazoa. The male glands are called antheridia in the cryptogams, pollen-sacs (formed from the microsporangia of the ferns) in the phanerogams, and testicles (_as spermaria_) in the metazoa. In many cases, especially in aquatic lower animals, the ovula (as products of the ovaries) are discharged directly outward. But, in most of the higher organisms, special sexual ducts (_gonoductus_) have been formed to conduct both kinds of the gonocyta out of the organism.

While the two kinds of sexual glands are usually located in different parts of the generating organism, there are, nevertheless, a few cases in which the sex-cells are formed directly and together from one and the same gland. These glands are called hermaphroditic glands. Such structures are very notable in several highly differentiated groups of the metazoa, and have clearly been developed from gonochoristic structures in lower forms. The class of crested medusæ, or ribbed medusæ (ctenophoræ), contains glasslike, sea-dwelling cnidaria of a peculiar and complicated build, which probably descend from hydromedusæ (or craspedota). But whereas the latter have very simple gonochoristic structures (four or eight monosexual glands in the course of the radial canals or in the gastric wall), in the ctenophoræ the eight hermaphroditic canals run in a meridian arch from one pole of the cucumber-shaped body to the other. Each canal corresponds to a ciliary streamer, and forms ovaries at one border and testicles at the other; and these are so arranged that the eight intercostal fields (the spaces between the eight streamers) are alternately male and female. Still more curious are the hermaphroditic glands of the highly organized, land-dwelling, and air-breathing lung-snails (_pulmonata_), to which our common garden snail (_arion_) and vineyard snail (_helix_) belong. Here we have a hermaphroditic gland with a number of tubes, each of which forms ovaries in its outer part and sperma in the inner. Still the two kinds of sex-cells lead separately outward.

In most of the lower and aquatic histona both kinds of sex-cells, when they are ripe, fall directly into the water, and come together there. But in most of the higher, and especially the terrestrial, organisms special exits or conducting canals have been formed for the sex-products, the sexual ducts (_gonoductus_); in the metazoa the female have the general name of oviducts and the male spermaducts (or _vasa deferentia_). In the viviparous histona special canals serve for the conveyance of the sperm to the ovum, which remains inside the mother's body; such are the neck of the archegonium in the cryptogams, the pistil in the phanerogams, and the vagina in the metazoa. At the outer opening of these conducting canals special copulative organs are developed, as a rule.

When the ejected sex-cells do not directly encounter each other (as in many aquatic organisms), special structures have to be formed to convey the fertilizing sperm from the male to the female body. This process of copulation becomes important, as it is associated with characteristic feelings of pleasure, which may cause extreme psychic excitement; as sexual love it becomes, in man and the higher animals, one of the most powerful springs of vital activity. In many of the higher animals (namely, vertebrates, articulates, and mollusks) there are also formed a number of glands and other auxiliary organs which co-operate in the copulation.

The manifold and intimate relations which exist, in man and the higher animals (especially vertebrates and articulates), between their sexual life and their higher psychic activity, have given rise to plenty of "wonders of life." Wilhelm Bölsche has so ably described them in his famous and popular work, _The Life of Love in Nature_, that I need only refer the reader to it. I will only mention the great significance of what are called "secondary sexual characters." These characteristics of one sex that are wanting in the other, and that are not directly connected with the sexual organs--such as the man's beard, the woman's breasts, the lion's mane, or the goat's horns--have also an æsthetic interest; they have, as Darwin showed, been acquired by sexual selection, as weapons of the male in the struggle for the female, and vice versa. The feeling of beauty plays a great part in this, especially in birds and insects; the beautiful colors and forms which we admire in the male bird of paradise, the humming-bird, the pheasant, the butterfly, etc., have been formed by sexual selection (_cf._ the _History of Creation_).

In various groups of the histona the male sex has become superfluous in the course of time; the ovula develop without the need of fertilization. That is particularly the case in many of the platodes (trematodes) and articulates (crustacea and insects). In the bees we have the remarkable feature that it is only decided at the moment of laying the egg whether it is to be fertilized or not; in the one event a female and in the other a male bee is formed from it. When Siebold proved at Munich these facts of miraculous conception in various insects, he was visited by the Catholic archbishop of the city, who expressed his gratification that there was now a scientific explanation possible of the conception of the Virgin Mary. Siebold had, unfortunately, to point out to him that the inference from the parthenogenesis of the articulate to that of the vertebrate was not valid, and that all mammals, like all other vertebrates, reproduce exclusively from impregnated ova. We also find parthenogenesis among the metaphyta, as in the _chara crinita_ among the algæ, the _antennaria alpina_ and the _alchemilla vulgaris_ among the flowering plants. We are, as yet, ignorant for the most part of the causes of this lapse of fertilization. Some light has been thrown on it, however, by recent chemical experiments (the effect of sugar and other water-absorbing solutions), in which we have succeeded in parthenogenetically developing unfertilized ova.

In the higher animals the complete maturity and development of the specific form are requisite for reproduction, but in many of the lower animals it has been observed recently that ovula and sperm-cells are even formed by the younger specimens in the larva stage. If impregnation takes place under these conditions, larvæ of the same form are born. And when these larvæ have afterwards reached maturity and reproduced in this form, we call the process _dissogony_ ("double-generation"). It is found in many of the cnidaria, especially the medusæ. But if larvæ propagate by unfertilized ova, and so reproduce their kind parthenogenetically, the process is known as _pædogenesis_ ("young-generation"). It is found particularly in the platodes (trematodes) and some of the insects (larvæ of _cecidomyca_ and other flies).

In a large number of lower animals and plants sexual and asexual generation regularly alternate. Among the protists we find this alternation of generation in the sporozoa; among the metaphyta in the mosses and ferns; and among the metazoa in the cnidaria, platodes, tunicates, etc. Often the two generations differ considerably in shape and degree of organization. Thus, in the mosses the asexual generation is the spore-forming moss capsule (_sporogonium_), while the sexual is the moss plant with stalk and leaves (_culmus_). In the case of the ferns, on the other hand, the latter is spore-forming and monogenetic, while the thallus-formed, simple, and small fore-germ (_prothallium_) is sexually differentiated. In most of the cnidaria a small stationary polyp is developed out of the ovum of the free-swimming medusa, and this polyp, in turn, generates by budding medusæ, which reach sexual maturity. In the tunicates (salpa) a sexual social form alternates with an asexual solitary form; the chain-salpa of the former are smaller and differently shaped than the large individual salpa of the latter, which again generate chains by budding. This special form of metagenesis was the first to be observed, as it was in 1819 by the poet Chamisso, when he sailed round the world. In other cases (for instance, in the closely related _doliolum_) a sexual generation alternates with two (or more) neutral ones. The explanation of these various forms of alternating generations is given in the laws of latent heredity (atavism), division of labor, and metamorphosis, and especially by the biogenetic law.

While in real metagenesis (alternation of generations in the strict sense) the asexual generation propagates by budding or spore-formation, this is done parthenogenetically in the cognate process of heterogenesis. This it is which, especially in many of the articulates, causes an immense increase of the species in a short time. Among the insects we have the leaf-lice (aphides), and among the crustacea the water-fleas (daphnides), that propagate in great numbers during warm weather by unfertilized "summer-ova." It is not until the autumn that males appear and fertilize the large "winter-ova"; in the following spring the first parthenogenetic generation issues from the winter eggs. The two heterogenetic generations are very different in the parasitic suctorial worms (trematodes). From the fertilized ovum of the hermaphrodite distoma we get simply constructed nurses (pædogenetic larvæ), inside which cercaria are generated from unfertilized ova; these travel, and are afterwards converted (inside another animal) into distoma once more.

I have given (_General Morphology_, chap, ii., p. 104) the name of strophogenesis to the complicated process of cell-reproduction, which we find in the ontogeny of most of the higher histona, both phanerogams and cœlomaria. In these there is not a real alternation of generations, as the multicellular tissue-forming organism develops directly from the impregnated ovum. But the process resembles metagenesis in so far as the ontogenetic construction consists itself in a repeated division of the cells. Many generations of cells proceed by cleavage from the one stem-cell (the impregnated ovum) before two of these cells become sexually differentiated, and form a generation of sexual cells. However, the essential difference consists in the fact that all these generations of cells--in the body of both the higher animals and the flowering plants--remain joined together as parts of a single bion (a unified physiological individual); but in the alternation of generations each group produced is made up of a number of bionta, which live as independent forms--often so different from each other that they were formerly thought to be animals of separate classes, such as the polyps and medusæ. Hence we must not describe the reproductive circle of the phanerogams as an alternation of generations, although it has started from the fern (by abbreviated heredity).

All simple forms of sexual reproduction without alternation of generations are comprised under the title of _hypogenesis_. The generative cycle proceeds from ovum to ovum in one and the same bion or physiological individual. This form of development is usual with most of the higher animals and plants; it may proceed with or without metamorphosis. The younger forms which arise temporarily in the latter case, and are distinguished from the sexually ripe form by the possession of the provisional (and subsequently disappearing) organs--larva organs (for instance, the tadpole or the pupa), are comprised under the general head of larvæ.

As a rule, only organisms of the same species seem to have sexual union and generate fertile progeny. This was formerly a rigid dogma, and served the purpose of defining the loose idea of the species. It was said: "When two animals or plants can have fertile offspring they belong to the same real species." This principle, which once afforded support to the dogma of the constancy of species, has long been discarded. We now know by numbers of sound experiments that not only two closely related species, but even two species of different genera, may have sexual intercourse in certain circumstances, and that the hybrids thus generated can have fertile offspring, either by union among themselves or with one of the parents. However, the disposition to hybridism varies considerably, and depends on the unknown laws of sexual affinity. This sexual affinity must be based on the chemical properties of the plasm of the copulating cells, but it seems to show a good deal of vagueness in its effect. As a rule, hybrids exhibit a combination of the features of both parents.

It has been proved by many recent experiments that hybrids have a more powerful build and can reproduce more strongly than pure offspring, whereas pure selection has generally in time an injurious effect. A freshening by the introduction of new blood seems to be good from time to time. Hence, it is just the reverse of what the former dogma of the constancy of species affirmed. The question of hybridism has, generally speaking, no value in defining the species. Probably many so-called "true species," which have relatively constant features, are really only permanent hybrids. This applies especially to lower sea-dwelling animals, the sexual products of which are poured into the water and swarm together in millions. As we know of various species of fishes, crabs, sea-urchins, and vermalia, that their hybrids are very easily produced and maintained by artificial impregnation, there is nothing to prevent us from believing that such hybrids are also maintained in the natural state.

The short survey we have made of the manifold varieties of reproduction is sufficient to give an idea of the extraordinary wealth of this world of wonders. When we go more closely into details we find hundreds of other remarkable variations of the process on which the maintenance of the species depends. But the most important point of all is the fact that all the different forms of tocogony may be regarded as connected links of a chain. The steps of this long ladder extend uninterruptedly from the simple cell-division of the protists to the monogony of the histona, and from this to the complicated amphigony of the higher organisms. In the simplest case, the cell-cleavage of the monera, propagation (by simple transverse division) is clearly nothing more than transgressive growth. But even the preliminary stage of sexual differentiation, the copulation of two equal cells (_gameta_), is really nothing but a special form of growth. Then, when the two gameta become unequal in the division of labor, when the larger inert macrogameton stores up food in itself, and the smaller, mobile microgameton swims in search of it, we have already expressed the difference between the female ovum and the male sperm-cell. And in this we have the most essential feature of sexual reproduction.

The reproduction of the organism is often regarded as a perfect mystery of life, and as the vital function which most strikingly separates the living from the lifeless. The error of this dualistic notion is clear the moment one impartially considers the whole gradation of forms of reproduction, from the simplest cell-division to the most elaborate form of sexual generation, in phylogenetic connection. It is obvious all through that transgressive growth is the starting-point in the formation of new individuals. But the same must be said of the multiplication of inorganic bodies--the cosmic bodies on the larger scale, crystals on the smaller scale. When a rotating sun passes a certain limit of growth by the constant accession of falling meteorites, nebulous rings are detached at its equator by centrifugal force, and form into new planets. Every inorganic crystal, too, has a certain limit of individual growth (determined by its chemical and molecular constitution). However much mother-water you add, this is never passed, but new crystals (daughter-crystals) form on the mother-crystal. In other words, growing crystals propagate.

XII

MOVEMENT

Mechanics as the science of motion (kinematics and phoronomism)--Chemistry of vital movement--Active and passive movements--Undulatory movement--Mechanism of imbibition--Autonomous and reflex movements--Will and willing--Mixed movements--Movements of growth--Direction of the vital movement--Direction of the crystallizing force--Direction of cosmic motion--Movements of protists--Amœboid, myophenous, hydrostatic, secretory, vibratory movements: cilia and lashes--Movements of histona, metaphyta, and metazoa--Locomotion of tissue animals: ciliary motion and muscular movements--Muscles of the skin--Active and passive organs of movement--Radiata, articulata, vertebrata, mammalia--Human movements.

All things in the world are in perpetual motion. The universe is a _perpetuum mobile_. There is no real rest anywhere; it is always only apparent or relative. Heat itself, which constantly changes, is merely motion. In the eternal play of cosmic bodies countless suns and planets rush hither and thither in infinite space. In every chemical composition and decomposition the atoms, or smallest particles of matter, are in motion, and so are the molecules they compose. The incessant metabolism of the living substance is associated with a constant movement of its particles, with the building up and decay of plasma-molecules. But here we must disregard all these elementary kinds of movement, and be content with a brief consideration of those forms of motion which are peculiar to organic life, and a comparison of them with the corresponding motions of inorganic bodies.

The science of motion, or mechanics, is now taken in very different senses: (1) in the widest sense as a philosophy of life [generally called mechanism or mechanicism in England], equivalent to either monism or materialism; (2) in the stricter sense as the physical science of motion, or of the laws of equilibrium and movement in the whole of nature (organic and inorganic); (3) in the narrowest sense as part of physics, or dynamics, the science of moving forces (in opposition to statics, the science of equilibrium); (4) in the purely mathematical sense as a part of geometry, for the mathematical definition of magnitudes of movement; and (5) in the biological sense as phoronomy, the science of the movements of organisms in space. However, these definitions are not yet universally adopted, and there is a good deal of confusion. It would be best to follow the lead of Johannes Müller, as we are going to do here, and restrict the name phoronomy to the science of the vital movements which are peculiar to organisms, in contrast to kinematics, the exact science of the inorganic movements of all bodies. The real material object of phoronomy is the plasm, the living matter that forms the material substratum of all active vital movements.

On our monistic principles the inner nature of organic life consists in a chemical process, and this is determined by continuous movements of the plasma-molecules and their constituent atoms. As we have already considered this metabolism in the tenth chapter, we need do no more here than point out that both the general phenomena of molecular plasma-movement and their special direction in the various species of plants and animals can be reduced in principle to chemical laws, and are subject to the same laws of mechanics as all chemical processes in organic and inorganic bodies. In this we emphasize our opposition to vitalism, which sees in the _direction_ of plasma-movement the supernatural influence of a mystical vital force or of some ghostly "dominant" (Reinke). We agree with Ostwald, who also reduces these complex movements to the play of energy in the plasm--that is to say, in the last instance to modifications of chemical energy. In regard to the visible movements of the living things which concern us at present, we must first distinguish passive and active, and subdivide the latter into reflex and autonomous.

Many movements of the living organism which the inexpert are inclined to attribute to life itself are purely passive; they are due either to external causes which do not proceed from the living plasm, or to the physical composition of the organic but no longer living substance. Purely passive movements, which play an important part in bionomy and chorology, comprise such as the flow of water and the rush of the wind; they cause considerable changes of locality and "passive" migrations of animals and plants. Purely physical, again, is what is known as the Brownian molecular movement which we observe with a powerful microscope in the plasm of both dead and living cells. When very fine granules (for instance, of ground charcoal) are equally distributed in a liquid of a certain consistency, they are found to be in a constant shaking or dancing movement. This movement of the solid particles is passive, and is due to the shocks of the invisible molecules of the fluid which are continually impinging upon each other. In the rhizopods--the remarkable protozoa whose unicellular organism sheds so much light on the obscure wonders of life--we notice a curious streaming of the granules in the living plasm. Within the cytoplasm of the amœbæ particles travel up and down in all directions. On the long thin plasma-threads or pseudopodia which stream out from the unicellular body of the radiolaria and thalamophora, thousands of fine particles move about, like promenaders in a street. This movement does not come from the passive granules, but from the active invisible molecules of the plasm, which are always changing their relative positions. Thus also the movements of the blood-cells which we can see with the microscope in the circulation of a young transparent fish, or in the tail of a frog-larva, are not due to the action of the blood-cells themselves, but to the flow of the blood caused by the beat of the heart.

An important factor in the life of many organisms, especially the higher plants, is the physical phenomenon called _imbibition_; it consists in the penetration of water between the molecules of solid bodies (drawn to them by molecular attraction), and the consequent displacement of the molecules by the fluid. In this way the volume of the solid body is increased, and movements are produced which may have the appearance of vital processes. The energy of these imbibitional bodies is notoriously very powerful; we can, for instance, split large blocks of stone by the insertion of a piece of wood dipped in water. As the cellulose membrane of plant-cells has this property of imbibition in a high degree (either in the living or the dead cell), the movements it causes are of great physiological importance. This is especially the case when the imbibition of the cell wall is one-sided, and causes a bending of the cell. In consequence of the unequal strain in the drying of many fruits, they split open and project their seeds to some distance (as do the poppy, snap-dragon, etc.). The moss-capsules also empty their spores as a result of imbibition-curving (in the teeth of the openings of the spore-cases). The hygroscopic points of the heron-bill (_erodium_) curl up in the dry state and stretch out when moist; hence they are used as hygrometers in the construction of meteorological huts. The so-called "resurrection plants" (_anastatica_, the rose of Jericho, and _selaginella lepidophylla_), which close up like a fist when dry, spread their leaves out flat when moistened (the leaves imbibing strongly on the inner side). There is no more real case of "resuscitation" (as many believe) in these cases than in the mythological resurrection of the body. However, these phenomena of imbibition are not active vital processes; they are independent of the living plasm, and due solely to the physical constitution of the dead cell-membranes.

In contrast with these passive movements of organisms, we have the active movements which proceed from the living plasm. In the ultimate analysis, it is true, these may be reduced to the action of physical laws just as well as the passive movements. But the causes of them are not so clear and obvious; they are connected with the complicated chemical molecular processes of the living plasm, of the physical regularity of which we are now fully convinced, though their complicated mechanism is not yet understood. We may divide into two groups the many different movements, which are called vital in this stricter sense, and were formerly regarded as evidences of the presence of a mystic vital force, according as the stimulus--the sensation of which is caused by the movement--is directly perceptible or not. In the first case, we have stimulated (or reflex or paratonic) movements, and in the second voluntary (autonomous or spontaneous) movements. As the will appears to be free in the latter, they have been left out of consideration by many physiologists, and handed over to the treatment of the metaphysical psychologist. On our monistic principles this is a grave error; nor is it improved when "psychonomism" appeals to a false theory of knowledge. On the contrary, the conscious will (and conscious sensation) is itself a physical and chemical process like unconscious and involuntary movement (and unconscious feeling). They are both equally subject to the law of substance. However, only the external stimuli which cause reflex movements are known to us to any great extent and experimentally recognizable; the internal stimuli, which affect the will, are mostly unknown, and are not directly accessible to investigation. They are determined by the complicated structure of the psychoplasm, which has been gradually acquired by phylogenetic processes in the course of millions of years.

The great problem of the will and its freedom--the seventh and last of Dubois-Reymond's world-riddles--has been dealt with fully in the _Riddle_ (chapter vii.). But as we still meet with the most glaring contradictions and confusion in regard to this difficult psychological question, I must touch upon it briefly once more. In the first place, I would remind the reader that it is best to restrict the name "will" to the purposive and conscious movements in the central nervous system of man and the higher animals, and to give the name of impulses (tropisms) to the corresponding unconscious processes in the psychoplasm of the lower animals, as well as of the plants and protists. For it is only the complicated mechanism of the advanced brain structure in the higher animals, in conjunction with the differentiated sense-organs on the one side and the muscles on the other, that accomplishes the purposive and deliberate actions which we are accustomed to call acts of will.

But the distinction between voluntary (autonomous) and involuntary (reflex) movements is as difficult to carry out in practice as it is clear in theory. We can easily see that the two forms of movement pass into each other without any sharp boundary (like conscious and unconscious sensation). The same action, which seems at first a conscious act of the will (for instance, in walking, speaking, etc.), may be repeated the next moment as an unconscious reflex action. Again, there are many important mixed or instinctive movements, the impulse to which comes partly from internal and partly from external stimuli. To this class belong especially the movements of growth.

Every natural body that grows increases its extent, fills a larger part of space, and so causes certain movements of its particles; this is equally true of inorganic crystals and the living organism. But there are important differences between the growth in the two cases. In the first place, crystals grow by the external apposition of fresh matter, while cells grow by the intussusception of fresh particles within the plasm (_cf._ chapter x.). In the second case, in growth, which determines the whole shape of the organism, two important factors always co-operate, the inner stimulus, which depends on the specific chemical constitution of the species, and is transmitted by heredity, and the external stimulus which is due to the direct action of light, heat, gravity, and other physical conditions of the environment, and is determined by adaptation (phototaxis, thermotaxis, geotropism, etc.).

A peculiar property of many vital movements (but by no means all) is the definite direction they exhibit; these are generally called purposive movements. For the teleologist they afford one of the chief and most welcome proofs of the dualistic theory of the older and the modern vitalism. Baer, especially, has laid stress on the purposiveness of all vital movement. It has been given a more precise expression recently by Reinke. His "dominants" are "intelligent directive forces," essentially different from all forms of energy or natural forces, and not subject to the law of substance. These metaphysical "vital spirits" are much the same as the immortal soul of dualistic psychology or the divine emanations of ancient theosophy. They are supposed not only to regulate the special development and construction of every species of animal and plant, and direct it to a predetermined end, but also to control all the various movements of the organism and its organs down to the cells. These "hyperenergetic forces" are equivalent to the "organizing principle" and the "unconscious will" of Edward Hartmann, the "arranging and controlling protoplasmic forces" of Hanstein and others. All these metaphysical, supernatural, and teleological ideas, like the older mystic notion of a special vital force, rest on a perversion of judgment by the apparent freedom of will and purposiveness of organization in the higher organisms. These thinkers overlook the fact that this purposiveness can be traced phylogenetically to simple physical movements in the lower organisms. Moreover, they overlook or deny the definite direction of inorganic forms of energy, though this is just as clear in the origin of a crystal as in the composition of the whole world-structure, in the direction of the mind as in the orbit of a planet. Hence it is important to bear in mind always these two forms of mechanical energy, and emphasize their identity with the direction of vital movement.

The force of gravitation which is at work in crystal-formation in the simple chemical body exhibits just as definite a direction as that which appears in the plasm in cell-construction. In this and other respects the comparison of the cell with the crystal, which was made even by the founders of the cell-theory, Schleiden and Schwann, in 1838, is thoroughly justified, though it is not correct in some other aspects. When the crystal is formed in the mother-water, the homogeneous particles of the chemical substance arrange themselves in a perfectly definite direction and order, so that mathematical planes of symmetry and axes arise within, and definite angles at the surface. On the strength of this, modern crystallography distinguishes six different systems of crystals. But, in different conditions, the same substance may crystallize in two or even three different systems (dimorphism and trimorphism of the crystal); thus, for instance, carbonate of lime crystallizes as calcspar in the hexagonal, and as arragonite in the rhombic system. If Reinke would be consistent, he ought to postulate a "dominant" for every crystal, to control the order and direction of the particles in its formation. He makes the curious statement (in 1899) that direction "is not a measurable magnitude" like energy, and so is not subject, like it, to the law of substance. We can mathematically determine the direction of the constructive force in the crystal just as well as in the cell.

If we comprise under the head of cosmokinesis the whole of the movements of the heavenly bodies in space, we cannot deny that they have a definite direction in detail, although our knowledge of this is still very incomplete. We can calculate the distances and speeds and movements of the planets round the sun with mathematical accuracy; and we gather from our astronomical observations and calculations that a similar regularity prevails in the movements of the other countless bodies in infinite space. But we do not know either the first impulse to these complex movements or their final goal. We can only conclude from the great discoveries of modern physics, supported by spectrum analysis and celestial photography, that the universal law of substance on the one side and the law of evolution on the other control the gigantic movements of the heavenly bodies just as they do the living swarm of tiny organisms that have inhabited our little planet for millions of years. Reinke ought, consistently, to admire the cosmic intelligence of the Supreme Being in these movements of the cosmic masses and its emanations, the "dominants," in the actual direction of their movements, as much as he does in the plasma-flow in the tiny organism.

The manifold gradation of vital movement which we find everywhere in the higher organisms is not without expression even in the protist realm. In this respect the chromacea, the simplest forms of vegetal monera, and the bacteria, which we regard as corresponding animal forms, developed from the former by metasitism, are of great interest. As microscopic scrutiny fails to detect any purposive organization in these unnucleated cells, and it is impossible to discover different organs in their homogeneous plasma-body, we have to look upon their movements as direct effects of their chemical molecular structure. But the same must be said also of a number of nucleated cells, both among the protophyta and the protozoa; only in this case the structure is less simple, in so far as both the nucleus itself and the surrounding cell-body exhibit, in indirect division, complicated movements in the plasm (caryokinesis). Apart from these, however, there is nothing to be seen in many unicellular beings (_e.g._, paulotomea, or calcocytea) that we need call "vital movement." On the border between the organic and inorganic worlds we have, as regards movement, the simplest forms of the chromacea, chroococcacea. We can see no vital movement in these structureless particles of plasm except slight changes of form, which occur when they multiply by cleavage. The internal molecular movements of the living matter, which effect their simple plasmodomous metabolism and growth, lie beyond our vision. The reproduction itself, in its simplest form of self-cleavage, seems to be merely a redundant growth, exceeding the limit of individual size for the homogeneous plasma-globule (_cf._ chapters ix. and x.).

The great majority of the protists have the appearance of real, nucleated cells. Hence we have to distinguish two different forms of movement in the unicellular organism--the inner movement in the caryoplasm of the nucleus and the outer in the cytoplasm of the cell-body; the two enter into close mutual relations during the remarkable process of partial resolution of the nucleus (caryolysis). In this modification and partial dissolution of their constituents we observe, during indirect cell-division, certain complicated movements (the significance of which is as yet entirely unknown), that are accomplished by both the granules of chromatin and the threads of achromin, and which are comprised under the head of nuclear movements (caryokinesis). It has lately been attempted to explain them on purely physical principles. The same may be said of the internal flow of the plasm which we find in the plasmodia of the amœbæ and mycetozoa, and in the endoplasm of many of the protophyta and protozoa.

The slow displacement of the molecules of plasm which is at the bottom of these plasma-movements also causes a variety of external changes of form in simple naked cells. Variable processes like folds or fingers (the "fold-feet," _lobopodia_) appear on their surface. As they are best observed in the common amœbæ (naked nucleated cells of the simplest kind), they are called amœboid movements. With these is connected the variable movement of the larger rhizopods, the radiolaria and thalamophora, in which hundreds of fine threads radiate from the surface of the naked plasma-body. A number of recent experts on the rhizopods, such as Bütschli, Richard Hertwig, Rhumbler, and others, have attempted to trace to purely physical causes this varying formation of pseudopodia, and their branching and net-like structure (without definite direction).

It is more difficult to do this in the case of the most highly differentiated of the protozoa, the infusoria. With these the free movement of the unicellular protozoon is farther advanced through the formation of permanent hairlike processes (long single lashes in the flagellata, and a number of short lashes in the ciliata) on the cell-surface and the movement of these by contraction and expansion, like the limbs, tentacles, and bones of the higher animals. The apparent spontaneity and various modulation in the ever-changing movements of these cell-feet is, in many of the infusoria, so like the autonomous voluntary movements in the metazoa that several experts on the infusoria have been moved on this account to ascribe individual (and even conscious) souls to them. Hence the difference between the various kinds of living movement is already very considerable before we leave the kingdom of the protists. On the one hand, the lowest monera (chromacea) join on directly to inorganic phenomena. On the other hand, the highly differentiated infusoria (ciliata) show so great a resemblance to the higher animals in their differentiated and autonomous movements that they have been credited with the possession of "free-will." There is no such thing as a sharp division.

In a large section of the higher protozoa differentiated organs of movement are developed, which may be compared to the muscles of the metazoa. In the cytoplasm threadlike, contractile structures are formed, and these have, like the muscular fibres of the metazoa, the power to contract and expand again in definite directions. These myophæna or myonema form, in many of the infusoria, both ciliata and flagellata, a special thin layer of parallel or crossed fibres underneath the exoplasm or the hyaline skin-layer of the cell. The metabolic body of the infusorium may be altered in various ways by the autonomous contraction of these. Special instances of these myophæna are the _myophrisca_ of the acantharia--contractile threads which surround the radial needles of these radiolaria like a crown. They are found in their outer gelatine envelope, the calymma, and by their contraction extend it, and so lessen the specific gravity.

Many of the aquatic protophyta and protozoa have the power of autonomous and independent locomotion, and this often has the appearance of being voluntary. Among the simplest fresh-water protozoa are the arcellina or thecolobosa (_difflugia_, _arcella_), little rhizopods that are distinguished from the naked amœbæ by the possession of a firm envelope. They usually creep about in the slime at the bottom, but in certain circumstances rise to the surface of the water. As Wilhelm Engelmann has shown, they accomplish this hydrostatic movement by means of a small vesicle of carbonic acid, which expands their unicellular body like an air-balloon; the specific weight of the cell-body, which is of itself heavier than water, is sufficiently lowered by this. The same method is followed by the pretty radiolaria which live floating (as plankton) at various depths of the sea. Their unicellular (originally globular) body is divided by a membrane into a firm inner central capsule and a soft outer gelatine covering. The latter, known as the calymma, is traversed by a number of water-vesicles or vacuoles. As a result of an osmotic process, carbonic acid may be secreted or pure water (without the salt of the sea-water) be imbibed in these vacuoles; by this means the specific gravity of the cell is lessened, and it rises to the surface. When it desires to make itself heavier and sink, the vacuoles discharge their lighter contents. These hydrostatic movements of the radiolaria (for which the myophrisca, still more complicated structures, have been developed in the acantharia) attain by simple means the same end that is accomplished in the siphonophora and fishes by air-filled and voluntarily contractile swimming-bladders.

Numbers of the unicellulars alter their position very characteristically by secreting a thick mucus at one side of their body and fastening this to the ground. If the secretion continues, a longish jelly-like stalk is produced by which the cell slowly pushes itself along, like a boat with a rowing-pole. This secretory locomotion is found, among the protophyta, in the desmidiacea and diatomes, and in some of the gregarinæ and rhizopods among the protozoa. The peculiar rolling movements of the oscillaria (threadlike chains of blueish-green unnucleated cells, closely related to the chromacea) are also effected by the secretion of mucus. On the other hand, it is probable that the sliding movements of many of the diatomes are due to fine processes (vibratory hairs?) in the plasm, which proceed either out of the seams (_raphe_) of the bivalvular silicious shells or through the fine pores in them.

Especially important in the easy and rapid locomotion of many unicellulars is the formation of fine hairlike processes at the surface of the body; in the broadest sense, they are called vibratory hairs. If only a few whiplike threads are formed, they are called _whips_ (_flagella_); if many short ones, _lashes_ (_cilia_). Flagelliform movement is found in some of the bacteria, but especially in the mastigophorous "whip-infusoria," in the mastigota among the protophyta, and the flagellata among the protozoa. As a rule, we have in these cases one or two (rarely more) long and very thin whip-shaped processes, starting from one pole of the long axis of the oval, round, or long cell-body. These whips (_flagella_) are set in vibratory motion (apparently often voluntary) in various ways, and serve not only for swimming or creeping, but also for feeling and securing food. Similar whip-cells (_cellulæ flagellatæ_) are also found very commonly in the body of tissue-animals, usually packed together in an extensive layer at the inner or outer surface (ciliated epithelium). If single cells are released from the group, they may live independently for some time, continuing their movements and resembling free infusoria. The same may be said of the travelling spores of many of the algæ, and of the most remarkable of all ciliated cells--the spermia or spermatozoa of plants and animals.

As a rule they are cone-shaped, having an oval or pear-shaped (though often also rod-shaped) head, which tapers into a long and thin thread. When their lively movements were first noticed in the male seminal fluid (each drop of which contains millions of them) two hundred years ago, they were thought to be real independent animalcules, like the infusoria, and so obtained their name of seed-animals (spermatozoa). It was a long time (sixty years ago) before we learned that they are detached glandular cells, which have the function of fertilizing the ovum. It was discovered at the same time that similar vibratory cells are found in many of the plants (algæ, mosses, and ferns). Many of the latter (for instance, the spermatozoids of the cycadea) have, instead of a few long whips, a number of short lashes (_cilia_), and resemble the more highly developed ciliated infusoria (_ciliata_).

The ciliary movement of the infusoria is held to be a more perfect form of vibratory movement, because the many short lashes found on them are used for different purposes, and have accordingly assumed different forms in the division of labor. Some of the cilia are used for running or swimming, others for grasping or touching, and so on. In social combinations we have the ciliated cells of the ciliated epithelium of the higher animals--for instance, in the lungs, nostrils, and oviducts of vertebrates.

In the unicellular, non-tissue forming protists, all the vital movements seem to be active functions of the plasm of the single cell; but in the histona, the multicellular tissue-forming organisms, they are the outcome of the combined movements of the many cells which compose the tissue. Careful anatomic study and experimental physiological scrutiny of the motor processes are, therefore, first directed, in the case of the histona, to clearing up the nature and activity of the special cells which compose the tissue, and then the structure and functions of the tissue itself. When we start from this point, and survey the manifold active motor phenomena of the histona as a whole, we see at once an essential agreement in the phoronomy of the two kingdoms of the metaphyta and metazoa, in the sense that at the lower stages the chemical and physical character of the motor processes can be clearly shown and can be traced to an interchange of energy in the plasm of the cells that make up the tissue. In the higher stages, however, we find striking differences, the voluntary character of many autonomous movements being very conspicuous in the higher animals, and thus the great problem of the freedom of the will is added to the purely physiological questions of stimulated movement, growth-movement, etc.

Moreover, the movements of the metazoa are much more varied and complicated than those of the metaphyta, in consequence of the higher differentiation of their sense-organs and the centralization of their nervous system. The former have generally free locomotion and the latter not. The special mechanism of the organs of movement is also very different in the two groups. In most of the metazoa the chief motor organs are the muscles, which have developed in the highest degree the power of definitely directed contraction and expansion. In most of the metaphyta, on the other hand, the chief part of the movements depend on the strain of the living plasm, or what is called the _turgor_ or expansibility of the plant-cells. This is effected by the osmotic pressure of the internal cell-fluid and the elasticity of the cellulose wall, which is thus expanded. Nevertheless, in both cases--and in all "vital" phenomena--the real cause of the process is, in the ultimate analysis, the chemical play of energy in the active plasm.

The metaphyta, with few exceptions, are fixed in one spot for life, or only mobile for a short time when they are young. In this they resemble the lower metazoa, the sponges, polyps, corals, bryozoa, etc. They have not free locomotion. The motor phenomena which we find in them affect only special parts or organs. They are mostly reflex or paratonic, and due to external stimuli. Only a few of the higher plants exhibit autonomous or spontaneous movement, the stimulating cause of which is unknown to us, and which may be compared to the apparently voluntary actions of the higher animals. The lateral feather-leaves of an Indian butterfly flower (_hedysarum gyrans_) move in circles through the air, like a pair of arms swinging, without any external cause; they complete a circle in a couple of minutes. Variations in the intensity of light have no effect on them. Similar spontaneous movements of the leaves of several species of clover (_trifolium_) and sorrel (_oxalis_) are performed only in the dark, not in the light. The terminal leaf of the meadow-clover repeats its rotation, which describes more than one hundred and twenty degrees of an arc, every two to four hours. The mechanical cause of these spontaneous "variation movements" seems to lie in variations of expansibility.

Voluntary and autonomous turgescence-movements of this kind are only observed in a few of the higher plants, but stimulated movements that are accomplished by the same mechanism are very common in the vegetal world. We have, especially, the well-known "sleep," or nyktitropic movements, of many plants. Many leaves and flowers hold themselves vertically to the streaming rays of the sun. When darkness comes on they contract, and the calices of the flowers close. Many flowers are open for only a few hours a day. The mechanism of turgescence, which effects these swelling movements, consists in the co-operation of the osmotic pressure of the internal cell-fluid and the elasticity of the strained cell-membrane enclosing the cytoplasm. The strain of the outer cellulose membrane on the plasmatic primordial sac within it grows so much on the accession of osmotically active matter that the internal pressure is equal to several atmospheres, and the elastic strained membrane stretches from ten to twenty percent. When water is withdrawn again from one of these swollen or turgescent cells, the membrane contracts; the cell becomes smaller, and the tissue looser. Other stimuli besides light (heat, pressure, electricity) may produce these expansional variations, and, as a consequence of it, certain reflex movements (or paratonic variational movements). The most striking and familiar examples are the flesh-eating fly-trap (_dionæa muscipula_) and the sensitive plant (_mimosa pudica_); their contraction is caused by mechanical stimuli, shaking, pressure, or the touching of the leaves.

Most of the higher animals have the power of free and voluntary locomotion. It is, however, wanting in some of the lower classes, which spend the greater part of their life at the bottom of the water, like plants. Hence these were formerly held to be vegetable--thus the sponges, polyps, and corals among the cœlenteria. A number of classes of the cœlomaria have also adopted the stationary life, such as the bryozoa and the spirobranchia among the vermalia, many mussels (oysters, etc.), the actinia among the tunicates, the sea-lilies (_crinoidea_) among the echinoderms, and even highly organized articulate, such as the tube-worms (_tubicolæ_), among the annelids, and the crawling crabs (_cirripedia_), among the crustacea. All these stationary metazoa move freely in their youth, and swim about in the water as _gastrulæ_, or in some other larva form. They have taken only gradually to stationary habits, and have been considerably modified, and often greatly degenerated, in consequence; for instance, in the loss of the higher sense-organs, the bones, and even of the whole head. Arnold Lang has shown this very clearly in his excellent work on the influence of stationary life on animals. The study of these retrogressive metamorphoses is very important for the theory of progressive heredity and selection; it also shows the great value of free locomotion for the higher sensitive and intellectual development of the animals and man.

In many of the lower aquatic metazoa the surface of the body is covered with vibratory epithelium--that is to say, with a layer of skin-cells which bear either one long whip (_flagellum_) or several short lashes (cilia). Flagellated epithelium is especially found in the cnidaria and platodes; ciliated epithelium mostly in the vermalia and mollusca. As the lashing motion of these hairlike processes brings a constant stream of fresh water to the surface of the body, they first of all effect respiration through the skin. But in many of the smaller metazoa they also serve the purpose of locomotion, as in the gastræads, the turbellaria, the rotifera, the nemertina, and the young larvæ of many other metazoa. The vibratory apparatus reaches its highest development in the _ctenophora_. The extremely delicate and soft body of these gherkin-shaped cnidaria swims slowly in the water by means of the strokes of thousands of tiny oar-blades. They are arranged in eight longitudinal rows which stretch from the mouth to the opposite pole. Each oar-blade consists of the long hair-lashes of a group of epithelial cells glued together.

The chief motor organs in the metazoa are the muscles which constitute the "flesh" of the body. Muscular tissue consists of contractile cells--that is to say, of cells with the sole property of contraction. When the muscular cell contracts, it becomes shorter and its diameter increases. This brings nearer together the two parts of the body to which its ends are attached. In the lower metazoa the muscle-cells have, as a rule, no particular structure; but in the higher animals the contractile plasm undergoes a peculiar differentiation, which has the appearance under the microscope of a transverse streaking of the long cells. On this ground a distinction is drawn between striated muscles and simple non-striated or smooth muscles. The more vigorous, rapid, and definite is the contraction of the muscle, the more marked is the streaky character, and the more pronounced the difference between the doubly refractive muscular particles from the simple refractive. The striated muscle is "the most perfect dynamo we know of" (Verworn). The normal heart of a man accomplishes every day, according to Zuntz, a work of about twenty thousand kilogrammetres--in other words, an energy that would suffice to lift to a height of one metre a weight of twenty thousand kilogrammes. In many flying insects (gnats, for instance) the flying muscles make three hundred to four hundred contractions a second.

In the lower and higher classes of the metazoa the muscle amounts to no more than a thin layer of flesh underneath the skin. This layer consists of muscular cells, which come originally from the ectoderm in the form of internal contractile processes of the skin-cells themselves, as in the polyps. In other cases the muscle-cells are developed from the connective-tissue cells of the mesoderm, the middle skin-layer, as in the ctenophora. This mesenchymic muscle is less common than epithelial muscle. In most of the askeletal vermalia the subdermal muscle divides into two layers--an outer deposit of concentric muscles and an inner layer of longitudinal muscles; in the cylindrical worms (nematodes, sagittæ, etc.) the latter fall into four longitudinal bands, one pair of upper (dorsal) and a pair of lower (ventral) muscular bands. At those parts of the body which are especially used for locomotion the muscle is more strongly developed, as in the belly-side of the crawling worms and mollusks. This muscular surface develops into a kind of fleshy "foot" (_podium_); it assumes a great variety of forms in the various classes of mollusks. In most of the snails which creep on the solid ground it grows into a muscular "flat-foot" (_gasteropoda_); in the mussels which cut like a plough through the soft slime it forms a sharp "hatchet-foot" (_pelecypoda_). The keel-snails (_heteropoda_) swim by means of a "keel-foot," which works like the screw of a ship; the floating-snails (_pteropoda_) swim unsteadily (like butterflies flying) by means of a pair of head-folds, which develop from the side of the anterior foot-section. In the highest mollusks, the cuttle-fishes (_cephalopoda_), this fore-foot divides into four or five pairs of folds, which grow into long and very muscular "head-arms"; the numbers of strong suckers on the latter have also special muscles. In all these non-articulate mollusks and vermalia hard skeletons are either altogether wanting or (like the external shells of the mollusks) they have no functional relation to the motor muscles. It is otherwise in the higher animals, in which we find this relation to a solid jointed skeleton that becomes a passive motor apparatus.

The higher groups of the animal kingdom in which a characteristic solid skeleton is developed and forms an important starting-point for the muscles, as well as a support and protection for the whole body, are the three stems of the echinoderms, articulates, and vertebrates. All three groups are very rich in forms, and far surpass all the other stems of the animal world in the perfection of their locomotive apparatus. However, the disposition and development of the skeleton as a passive support, and the correlation of the muscles to it as active pulling-organs, differ very much in the three classes, and are the chief factors in determining their characteristic types; they show clearly (even apart from other radical differences) that the three stems have arisen independently of each other from three different roots in the vermalia-stem. In the echinoderms the calcareous skeleton is formed from chalky deposits in the corium, in the articulates from chitine secretions of the epidermis, and in the vertebrates from cartilage of an internal chord-sheath (_cf._ _Anthropogeny_, chapter xxvi.).

The remarkable stem of the sea-dwelling echinoderms or "prickly skins" is distinguished from all the other animal groups by a number of striking peculiarities; prominent among these are the special formation of their active and passive motor organs and the curious form of their individual development. In this ontogenesis two totally different forms appear successively--the simple astrolarva and the elaborately organized and sexually mature astrozoon. The small, free-swimming astrolarva has the general structural features of the rotatoria, and so shows, in accordance with the biogenetic law, that the original stem-form of the echinoderms (the amphoridea) belonged to this group of the vermalia. I have briefly explained these structures in the _History of Creation_ (chapter xxii.), and more fully in my essay on the amphoridea and cystoidea (1896). The little astrolarva has no muscles, and no water-vessels or blood-vessels. It moves by means of vibratory lashes or bands, which are attached to special armlike processes at the surface. These arms are regularly developed to the right and left of the bilateral symmetrical larva (which as yet shows no trace of the five-rayed structure). By a very curious modification the small bilateral astrolarva is transformed into the totally different pentaradial astrozoon, the large sexually mature echinoderm with a pronounced five-rayed structure. (See _Art-forms in Nature_, plates 10, 20, 30, 40, 60, 70, 80, 90, and 95.) It has a most elaborate organization, with muscles and cuticular skeleton, blood-vessels and water-vessels, etc. A section of the astrozoa--the living crinoidea, or sea-lilies, and the extinct classes of blastoidea (sea-buds), cystoidea (sea-apples), and amphoridea (sea-urns)--grow in stationary fashion at the bottom of the sea. The other four extant classes creep about in the sea--the sea-gherkins (holothuria), the star-fish (asteridea and ophoidea), and the sea-urchins (echinidea). Their creeping motion is accomplished by two kinds of organs--water-feet and skin-muscles. The latter find their support and attachment in solid calcareous needles, which develop from chalky deposits in the corium. As these calcareous needles (which are particularly conspicuous in the sea-urchin) are set movably in special protuberances of the calcareous plates of the cuticular skeleton, and moved by little muscular needles, the echinoderms walk on them as if they were stilts. Between these, however, a number of water-feet arise from inside--thin tubes like the fingers of a glove, which are filled with water by an internal conduit-system (the so-called ambulacral system) and become stiff. These very extensible ambulacral feet, often provided with a suctorial plate at the closed outer end, serve for creeping, sucking, touching, and grasping. As these distinctive motor organs of the echinoderms--both the ambulacral feet with their complicated water-tubes and the movable needles with their joints and muscles--are found in hundreds, often in thousands, on every individual five-rayed astrozoon, we might say that the echinoderms have the most advanced and complicated motor organs of all animals. Their historical development is perfectly understood from its earliest stages, since Richard Semon found, in his ingenious pentact æatheory (1888), the correct phylogenetic meaning of the curious embryology of the echinoderms discovered in 1845 by Johannes Müller. I endeavored in 1896 to establish it in detail, in relation to paleontological discoveries, in the essay I have mentioned.

The large stem of the articulata (the richest in forms of all the animal stems) comprises three chief classes--the annelids, crustacea, and tracheata. All three groups agree in the essential features of their organization, especially in the external articulation or metamerism of the long bilateral body, and also in the repetition of the internal organs in each joint or segment. In each joint there is originally a knot of the ventral nervous system (the ventral marrow), a chamber of the dorsal heart, a chitine-ring of the cutaneous skeleton, and a corresponding group of muscles.

Of the three great classes of the articulates the annelids are developed directly from the vermalia, of which both the nematoda and nemertinæ approach very closely to them. The two other and more highly organized classes, the crustacea and tracheata, are younger groups, independently evolved from two different stems of the annelids. The annelids, or "ringed-worms" (to which, _e.g._, the rain-worms belong), have mostly a very homogeneous articulation; their segments or metamera repeat the same structure to a great extent, especially the subdermal muscles. In a transverse section we see in every joint underneath the layer of concentric muscles a pair of dorsal and a pair of ventral muscles. Their epidermis has secreted a thin covering of chitine, in the tubular worms a leather-like or calcified tube. There are no bones in the oldest annelids; in the younger bristle-worms (_polychæta_) one or two pairs of short unjointed feet (_parapodia_) are found in every joint.

The other two chief classes of the articulates develop long and jointed feet of very varied forms, and at the same time assume different shapes of limbs in the division of labor. This heterogeneous articulation (heteronomy) is the more pronounced the higher the whole organization. This is equally true of the aquatic, gill-breathing crustacea (crabs, etc.) and the tracheata (terrestrial animals breathing through a trachea, the myriopods, spiders, and insects). In the higher groups of both classes the number of limbs is usually not higher than fifteen to twenty; and they are distributed in three principal sections--head, breast, and posterior part of the body. The firm covering of chitine, which was delicate and thin in most of the annelids, is much thicker in most of the crustacea and tracheata, and often hardened by a calcareous deposit; it forms a solid ring of chitine in each segment, inside which the motor muscles are attached. The successive hard rings are connected by thin, mobile, intermediate rings, so that the whole body combines firmness, elasticity, and mobility in a high degree. The structure of the long jointed legs, which are fixed in pairs on each segment, is very similar. Hence the typical character of the motor organs of the crustacea lies in the circumstance that both in the body and the limbs the muscles are attached to the interior of hollow chitine tubes, and go in these from member to member.

The vertebrates are just the reverse in structure. In their case a solid internal skeleton is formed in the longitudinal axis of the body, and the muscles are external to these supporting organs. The articulation or metamerism itself is not visible externally in the vertebrates; it is only seen in the muscular system when the non-articulated skin has been removed. Then, even in the lowest skull-less vertebrates, the acrania, the internal skeleton of which consists merely of a cylindrical, solid, and elastic axial rod (_chorda_), we see on each side a row of muscular plates (fifty to eighty in the amphioxus). In this case there are not pairs of limbs, and it is the same with the oldest craniate animals, the cyclostoma (myxinoida and petromyzonta). It is only with the third class of the vertebrates, the true fishes (_pisces_), that two pairs of lateral limbs appear--the breast-fins and belly-fins. From these, in their terrestrial descendants, the oldest amphibia of the Carboniferous Period, the two pairs of jointed legs--fore-legs (carpomela) and hind-legs (tarsomela)--are derived. These four lateral five-toed legs have a very characteristic and complicated articulation, both in the internal bony skeleton and the muscular system that encloses this and is attached to it. From the amphibia, the earliest quadrupeds, this locomotive apparatus is transmitted by heredity to their descendants, the three higher classes of the vertebrates, reptiles, birds, and mammals. As I have dealt with these important structures fully in my _Anthropogeny_ (chapter xxvi.), and given a number of illustrations of them, I must refer the reader to that work,[8] and will only make a few observations on the mammals.

Both parts of the motor apparatus, the internal bony skeleton (the passive supporting apparatus) and the external muscular system (the active motor), exhibit a great variety of construction within the mammal class, in consequence of adaptation to the most different habits and functions. We have only to compare the running carnivora and ungulata, the leaping kangaroos and jerboas, the burrowing moles and hyperdæi, the flying cheiroptera and bats, the fishlike swimming sirens and whales, and climbing lemures and apes. In all these and the remaining orders of the mammals the whole regular structure of the motor apparatus is strikingly adapted to the habits of life which have been formed by this adaptation itself. Nevertheless, we see that the essential character of the inner organization which distinguishes the mammals as a class is not affected by this adaptation, but constantly maintained by heredity. These recognized facts of comparative anatomy and ontogeny, and the concordant results of paleontology, prove convincingly that all living and fossil mammals, from the lowest ungulates and marsupials to the ape and man, have descended from one common stem-form, a pro-mammal, that lived in the Triassic Period; its earlier ancestors in the Permian Period were reptiles, and, in the Carboniferous Period, amphibia. Among the characters of the locomotive apparatus which are peculiar to mammals we have, on the one hand, the structure of the vertebral column and the skull, and, on the other hand, the formation of the muscles which are attached to these supporting organs. In the skull we particularly notice the formation of the lower jaw and the joint by which it is connected with the temporal bone. This joint is temporal, and so distinguished from the square joint of the other vertebrates. The latter is found in the mammals in the tympanic cavity of the middle-ear, between the hammer (the modified joint of the lower jaw, _articulare_) and the anvil (the original _quadratum_). In harmony with this remarkable modification of the maxillary joint, the corresponding muscles have naturally also undergone a considerable transformation. A distinctive muscle that is only found in the mammals and regulates their respiration is the diaphragm, which completely divides the abdominal and thoracic cavities; the various muscles, from the blending of which it has been formed, still remain separate in the other vertebrates.

The many organs by means of which our human organism accomplishes its manifold movements are just the same as in the apes, and the mechanism of their action is in no way different. The same two hundred bones, in the same order and composition, form our internal bony skeleton; the same three hundred muscles effect our movements. The differences we find in the form and size of the various muscles and bones (and which are, as is well known, also found between lower and higher races of men) are due to differences in growth in consequence of divergent adaptation. On the other hand, the complete agreement in the construction of the whole motor apparatus is explained by heredity from the common stem-form of the apes and men. The most striking difference between the movements of the two is due to man's adaptation to the erect posture, while the climbing of trees is the normal habit of the ape. However, it is unquestionable that the former is an evolution from the latter. A double parallel to this modification is seen in the jerboa among the ungulates, and in the kangaroo among the marsupials. Both these, in springing, use only the strong hinder extremities, and not the weaker fore-limbs; as a result of this their posture has become more or less erect. Among the birds we have an analogous case in the penguins (_aptenodytes_); as they no longer use their atrophied wings for flight, but only in swimming, they have developed an erect posture when on land.

The human will is also not specifically different from that of the ape or any other mammal; and its microscopic organs, the neurona in the brain and the muscular cells in the flesh, work with the same forms of energy, and are similarly subject to the law of substance. Hence it is immaterial for the moment whether one believes in the freedom of the will according to the antiquated creed of indeterminism, or whether one holds it to be refuted scientifically by the arguments of modern determinists; in either case the acts of the will and voluntary movements follow the same laws in man as in the ape. The high development of the function in civilized man, the ample differentiation of speech and morality, art and science--in a word, the ethical significance of the will for higher culture--is in no way discordant to this monistic and zoologically grounded conception. In the lower races these privileges of the civilized will are only found in a slight degree, and some of them are wholly wanting among the lowest races. The distance between the lowest savage and the most civilized human being is greater, in this respect also, than that which separates the savage from the anthropoid ape. However, I refer the reader to the remarks I made at the close of the seventh chapter of the _Riddle_ on the problem of the freedom of the will and the infinite literature relating thereto. The reader who desires to go further into this subject will find it well treated in the works of Traugott Trunk (1902) and Paul Rée (1903) [also in Dr. Stout's recent little manual of psychology and Mr. W. H. Mallock's _Religion as a Credible Doctrine_].

XIII

SENSATION

Sensation and consciousness--Unconscious and conscious sensation--Sensibility and irritability--Reflex sensation and perception of stimuli--Sensation and living force--Reaction to stimuli--Resolution of stimuli--External and internal stimuli--Conveyance of stimuli--Sensation and striving--Sensation and feeling--Inorganic and organic sensation--Light sensation, phototaxis, sight--Sensation of warmth, thermotaxis--Sensation of matter, chemotaxis--Taste and smell--Erotic chemicotropism--Organic sensations--Sensation of pressure--Geotaxis--Sensation of sound--Electric sensation.

Sensation is one of those general terms that have at all times been liable to the most varied interpretations. Like the cognate idea of the "soul," it is still extremely ambiguous. During the eighteenth century it was generally believed that the function of sensation was peculiar to animals, and was not present in plants. This opinion found its most important expression in the well-known principle in Linné's _Systema Naturæ_: "Stones grow: plants grow and live: animals grow, live, and feel." Albrecht Haller, who gathered up all the knowledge of his time relating to organic life in his _Elementa Physiologiæ_ (1766), distinguished as its two chief characters "sensibility" and "irritability." The one he ascribed exclusively to the nerves, and the other to the muscles. This erroneous idea was subsequently refuted, and in our own time irritability is conceived to be a general property of all living matter.

The great advance made by the comparative anatomy and experimental physiology of animals and plants in the first half of the nineteenth century brought to light the fact that irritability or sensibility is a common quality of all organisms, and that it is one of the principal characteristics of vital force (_cf._ chapter ii.). The greatest merit in connection with its experimental study attaches to the famous Johannes Müller. In his classical _Manual of Human Physiology_ (1840) he established his theory of the specific energy of the nerves and their dependence on the sense-organs on the one hand and the mental life on the other. He devoted the fifth chapter of his book to the former and the sixth to the latter, approaching particularly to Spinoza in his general psychological views; he treated psychology as a part of physiology, and thus put on a sound scientific basis that naturalistic conception of the place of psychology in the biological system which we now regard as the correct view. At the same time he proved that sensation is a function of the organism as much as movement or nutrition.

The view of sensation that prevailed in the second half of the nineteenth century was very different. On the one hand the experimental and comparative physiology of the sense-organs and the nervous system immensely enriched our exact knowledge by the invention of ingenious methods of research and the use of the great advance made by physics and chemistry. The famous investigations of Helmholtz and Hertwig on the physics of the senses, of Matteucci and Dubois-Reymond on the electricity of the muscles and nerves, and the great progress made in vegetal physiology by Sachs and Pfeffer, and in physiological chemistry by Moleschott and Bunge, enabled us to realize that even the most mysterious of the wonders of life depend on physical and chemical processes. By the application of the different stimuli--light, heat, electricity, and chemical action--to the various sensitive or irritable organs under definitely controlled conditions, scientists succeeded in subjecting with exactness a great part of the phenomena of stimulation to mathematical measurements and formulæ. The science of the stimuli and their effects acquired a strictly physical character.

On the other hand, in most striking contradiction to the immense advance of experimental physiology, we see that the general conception of the various vital processes, and especially of the inner nerve-action that converts the functions of the senses into mental life, is most curiously neglected. Even the fundamental idea of sensation, which plays the chief part in it, is disregarded more and more. In many of the most valuable modern manuals of physiology, containing long chapters on stimuli and stimulation, there is little or no mention of sensation as such. This is chiefly due to the mischievous and unjustifiable gulf that has once more been artificially created between physiology and psychology. As the "exact" physiologists found the study of the inner psychic processes which take place in sense-action and sensation inconvenient and unprofitable, they gladly handed over this difficult and obscure field to the "psychologists proper"--in other words, to the metaphysicians, who had for the starting-point of their airy speculations the belief in an immortal soul and divine consciousness. The psychologists readily abandoned the inconvenient burden of experience and _a posteriori_ knowledge, to which the modern anatomic physiology of the brain laid special claim.

The greatest and most fatal error committed by modern physiology in this was the admission of the baseless dogma that all sensation must be accompanied by consciousness. As most physiologists share the view of Dubois-Reymond, that consciousness is not a natural phenomenon, but a hyperphysical problem, they leave it and this inconvenient "sensation" outside the range of their researches. This decision is, naturally, very agreeable to the prevalent metaphysics; it has just as much interest in the transcendental character of sensation as in the liberty of the will, and thus the whole of psychology passes from the empirical province of natural science into the mystical province of mental science. For its foundation they then take the "critical theory of knowledge," which ignores the results of the real physiological organs--the senses, nerves, and brain--and draws its "superior wisdom" from the inner mirroring of self by the introspective analysis of presentations and their associations. It is extraordinary that even distinguished monistic physiologists suffer themselves to be taken in with this sort of metaphysical jugglery, and dismiss the whole of psychology from their province; their psychomonism readmits the soul as a supernatural entity, and delivers it, in contrast with the "world of bodies," from the yoke of the law of substance.

Impartial reflection on our personal experience during sensation and consciousness will soon convince us that these are two different physiological functions, which are by no means necessarily associated; and the same may be said of the third principal function of the soul--the will. When we learn an art--for instance, painting or playing the piano--we need months of daily practice in order to become expert at it. In this we experience every day hundreds of thousands of sensations and movements which are learned and repeated with full consciousness. The longer we continue the practice and the more we adapt and accustom ourselves to the function, the easier and less conscious it becomes. And when we have practised the art for some years, we paint our picture or play our piano unconsciously; we think no longer of all the small, subtle shades of sensation and acts of will which were necessary in learning. The mere impulse of the will to paint the picture once more or play the piece again suffices to release the whole chain of complicated movements and accompanying sensations which had originally to be learned slowly, laboriously, and with full consciousness. An experienced pianist plays the most difficult piece--if he has learned it and repeated it thousands of times--"half in a dream." But it needs only a slight accident, such as a mistake or a sudden interruption, to bring back the wandering attention to the work. The piece is now played with clear consciousness. The same may be said of thousands of sensations and movements which we learned at first consciously in childhood, and then repeat daily afterwards without noticing--such as in walking, eating, speaking, and so on. These familiar facts prove of themselves that consciousness is a complicated function of the brain, by no means necessarily connected with sensation or will. To bind up the ideas of consciousness and sensation inseparably is the more absurd, as the mechanism or the real nature of consciousness seems very obscure to us, while the idea of it is perfectly clear: we know that we know, feel, and will.

The word "irritability" is generally taken by modern physiology to mean that the living matter has the property of reacting on stimuli--that is to say, of responding by changes in itself to changes in its environment. The stimulus, or action of a foreign energy, must, however, be felt by the plasm before the corresponding stimulated movement (in the form of various manifestations of energy) will be produced. Hence the question whether this sensation is (in certain cases) associated with consciousness or (generally) remains unconscious is of a subordinate interest. The plant that is caused to open its floral calyx by the stimulus of light acts just as unconsciously in this as the coral that spreads out its crown of tentacles under the same influence; and when the sensitive carnivorous plant (_dionæa_ or _drosera_) closes its leaves in order to catch and destroy the insect sitting on them, it acts in the same way as the sensitive actinia or coral when it draws in its crown of tentacles for the same object--in both cases without consciousness! We call these unconscious movements "reflex actions." I have dealt somewhat fully with these reflex movements in the seventh chapter of the _Riddle_, and must refer the reader thereto. This elementary psychic function always depends on a conjunction of sensation and movement (in the widest sense). The movement that the stimulus provokes is always preceded by a sensation of the influence exerted.

Modern physiology makes desperate efforts to avoid the use of the word "sensation" and substitute for it "perception of stimulus." The chief blame for this misleading expression is due to the arbitrary and unjustified separation of psychology from physiology. The latter is supposed to occupy itself with the material phenomena and physical changes, leaving to psychology the privilege of dealing with the higher mental phenomena and metaphysical problems. As we reject this distinction altogether on monistic principles, we cannot consent to separate sensation from the perception of stimuli--whether this sensation be accompanied with consciousness or not. Moreover, modern physiology, in spite of its desire to keep clear of psychology, sees itself compelled in a thousand ways to use the words "sensation" and "sensitive," especially in the science of the organs of sense.

What we call sensation or perception of stimuli may be regarded as a special form of the living force or actual energy (Ostwald). Sensitiveness or irritability, on the other hand, is a form of virtual or potential energy. The living substance at rest, which is sensitive or irritable, is in a state of equilibrium and indifference to its environment. But the active plasm, that receives and feels a stimulus, has its equilibrium disturbed, and corresponds to the change in its environment and its internal condition. This response of the organism to a stimulus is called "reaction"--a term that is also used (in the same sense) in chemistry to express the interaction of bodies on each other. At each stimulation the virtual energy of the plasm (sensitiveness) is converted into living or kinetic force (sensation). The share of the stimulus in this conversion is described as a "release" of energy.

The term "reaction" stands in general for the change which any body experiences from the action of another body. Thus, for instance, to take the simplest case, the interaction of two substances in chemistry is called a reaction. In chemical analysis the word is used in a narrower sense to denote that action of one body on another which serves to reveal its nature. Even here we must assume that the two bodies feel their different characters; otherwise they could not act on each other. Hence every chemist speaks of a more or less "sensitive reaction." But this process is not different in principle from the reaction of the living organism to outer stimuli, whatever be their chemical or physical nature. And there is no more essential difference in psychological reaction, which is always bound up with corresponding changes in the psychoplasm, and so with a chemical conversion of energy. In this case, however, the process of reaction is much more complicated, and we can distinguish several parts or phases of it: 1, the outer excitation; 2, the reaction of the sense-organ; 3, the conducting of the modified impression to the central organ; 4, the internal sensation of the conducted impression; and, 5, consciousness of the impression.

The important idea of a release of energy--the term we give to the effect of the stimulus--is also used in physics. If we put a piece of burning wood in a barrel of powder, the flame causes an explosion. In the case of dynamite a simple mechanical shock is enough to produce the most enormous expenditure of force in the explosive matter. When we discharge a bow the slight pressure of the finger on the tense cord suffices to send out the arrow or bolt on its deadly mission. So also a sound or a ray of light that strikes the ear or eye suffices to bring about a number of complex effects by means of the nervous system. In the fertilization of the ovum by the male sperm the chemical conjunction of the two formative principles is sufficient to cause the growth of a new human being out of the microscopic plasma-globule, the stem-cell (_cytula_). In these and thousands of other reactions a very slight shock suffices to provoke the largest effects in the stimulated substance. This shock, which we call a release of energy, is not the direct cause of the considerable result, but merely the occasion for bringing it about. In these cases we have always a vast accumulation of virtual energy converted into living force or work. The magnitude of the two forces has no relation at all to the smallness of the shock which led to the conversion. In this we have the difference between stimulated action and the simple mechanical action of two bodies on each other, in which the quantity of the energy expended is equal on both sides, and there is no stimulus.

The immediate effect of a stimulus on living matter can best be followed in external physical or chemical stimuli, such as light, heat, pressure, sound, electricity, and chemical action. In these cases physical science is often able to reduce the life-process to the laws of inorganic nature. This is more difficult with the internal stimuli within the organism itself, which are only partly exposed to physiological investigation. It is true that here also the task of science is to reduce all the biological phenomena to physical and chemical laws. But it can only discharge a part of this difficult task, as the phenomena are too complicated, and their conditions too little known in detail, to say nothing of the crudeness and imperfectness of our methods of research. Yet, in spite of all this, comparative and phylogenetic physiology convinces us that even the most complicated of our internal excitations, and particularly the mental activity of the brain, depend just as much as the outer stimulations on physical processes, and are equally subject to the law of substance. This is, in fact, true of reason and consciousness.

In man and all the higher animals the stimuli are received by the organs of sense and conducted by their nerves to the central organ. In the brain they are either converted into specific sensations in the sense-centres, or conveyed to the motor region, where they provoke movements. The conduction of stimuli is simpler in the lower animals and the plants; the tissue-cells either directly affect each other or are connected by fine threads of plasm. In the unicellular protists the stimulus which strikes one particular spot of the surface may be immediately communicated to the other parts of the unified plasmic body.

We shall see in the course of our inquiry that the simplest form of sensation (in the widest sense) is common to inorganic and organic bodies, and thus that sensitiveness is really a fundamental property of all matter, or, more correctly, all substance. We may, therefore, ascribe sensation to the constituent atoms of matter. This fundamental thought of hylozoism, expressed long ago by Empedocles, has lately been very definitely urged, especially by Fechner. However, the able founder of psychophysics (_cf._ the _Riddle_, p. 35) assumes that consciousness (or thought, in the Spinozistic sense) always accompanies this universal property of sensation. In my opinion, consciousness is a secondary psychic function, only found in man and the higher animals, and bound up with the centralization of the nervous system. Hence it is better to speak of the unconscious sensation of the atoms as _feeling_ (_æsthesis_), and their unconscious will as _inclination_ (_tropesis_). It finds expression in the one-sided action of a stimulus as a "directed movement" or "stimulated movement" (_tropismus_ or _taxis_).

The familiar ideas of sensation and feeling are often confused, and employed in very different ways in both physiology and psychology. The metaphysical tendency which so completely separates the two sciences, and the physiological tendency which agrees with it, regard feeling as a purely psychic or spiritual function, whereas in the case of sensation they have to admit the connection with bodily functions, especially sense-action. In my opinion, the two ideas are purely physiological and cannot be sharply separated, or only in the sense that sensation relates more to the external (objective) part of the sensory nerve-process, and feeling to the internal (subjective) part. Hence we may define the difference in a general way by saying that sensation perceives the different qualities of the stimuli, and feeling only the quantity, the positive or negative action of the stimulus (pleasure or pain). In this last and widest sense we may ascribe the feeling of pleasure and pain (in the contact with qualitatively differing atoms) to all atoms, and so explain the elective affinity in chemistry (synthesis of loving atoms, inclination; analysis of hating atoms, disinclination).

Our monistic system (whether it be taken as energism or materialism, or more correctly as hylozoism) regards all substance as having "soul"--that is to say, endowed with energy. In the chemical analysis of organisms we do not find any elements that are not found in inorganic nature; we find that the movements in organisms obey the same laws of mechanics as the latter; we believe that the conversion of energy in the living matter occurs in the same way, and is provoked by the same stimuli, as in inorganic matter. We are forced to conclude from. these experiences that the perception of stimuli--sensation in the objective and feeling in the subjective sense--is also generally present in the two. All bodies are in a certain sense "sensitive." It is just in this dynamic conception of substance that monism differs essentially from the materialistic system, which regards one part of matter as "dead" and insensitive. In this we have the best means of joining consistent materialism or realism with consistent spiritualism or idealism. But, as a first condition of such a union, we must demand a recognition that organic life is subject to the same general laws as inorganic nature. In both cases the outer world acts alike as a stimulus on the inner world of the body. We can easily see this if we glance at the various kinds of sensation which correspond to the various kinds of stimuli. Light and heat, external and internal chemical stimuli, pressure and electricity, cause analogous sensations and modifications in their effect on organic and inorganic bodies.

The effect which the light-stimulus has on living matter, the sensation of light that results, and the chemical changes of energy that follow, are of great physiological importance in all organisms. We might even say that sunlight is the first, oldest, and chief source of organic life; all other exertions of force depend in the long run on the radiant energy of sunlight. The oldest and most important function of plasm--one which is at the same time a cause of its formation--is carbon-assimilation; and this plasmodomism is directly dependent on sunlight. If it acts in a one-sided way, it causes the particular form of stimulation which we call phototaxis or heliotropism. This is of a positive character--that is to say, they turn towards the source of the light--in the great majority of organisms, both protists and histona. Everybody knows that flowers that are growing in the window of a room turn to the light. However, many organisms which have grown accustomed to living in the dark are heliotropically negative; they shun the light and seek darkness, such as the fungi, many lucifugous mosses and ferns, and many deep-sea animals.

The principal organs of light-sensation in the higher animals are the eyes; they are wanting in many of the lower animals as well as the plants. The essential difference between the real eye and a part of the skin that is merely sensitive to light is that the eye can form a picture of objects in the outer world. This faculty of vision begins with the formation of a small convergent lens, a biconvex refracting body at a certain spot on the surface. Dark pigment-cells which surround it absorb the light-rays. From this first phylogenetic form of the organ of vision up to the elaborate human eye there is a long scale of evolutionary stages--not less extensive and remarkable than the historical succession of artificial optical instruments from the simple lens to the complicated modern telescope or microscope. This great "wonder of life"--the long scale of the evolution of the eye--has an interesting tearing on many important questions of general physiology and phylogeny. We can, in this case, see clearly how a very complicated and purposive apparatus can arise in a purely mechanical way, without any preconceived design or plan. In other words, we can see how an entirely new function--and one of its principal functions, vision--has arisen in the organism by mechanical means.

The advanced vision of the higher animals is made up of a great number of different functions, with a corresponding complexity of detail in the anatomic structure of the eye. No other organ, after the brain, is so necessary as the eye for the multifarious vital activities of the higher animals, and especially for the mental life of civilized man and the progress of art and science. What would the human mind be if we could not read, write, and draw, and have a direct knowledge through the eye of the forms and colors of the outer world? Yet this invaluable structure is only the highest and most perfect stage in the long chain of evolutionary processes which has its starting-point in the general sensitiveness to light, or the photic irritability of plasm. However, we find a number of varieties and grades of this even among the unicellular protists, and, indeed, the very lowest and oldest of the protists, the monera. Various species of both the chromacea and the bacteria are heliotropic to different degrees, and have a fine sensitiveness to the strength of the light stimulus.

The stimulating effect which light has on the homogeneous plasm of the monera is also found in a number of inorganic bodies. In these cases the photic stimulus produces partly chemical and partly mechanical changes. Every chemist speaks of substances that are more or less "sensitive" to light; the photographer speaks of his "sensitive plates," the painter of his "sensitive colors." Many chemical compounds are so sensitive to light that they are destroyed at once in sunlight, and so have to be kept in the dark. There is no other word but "sensation" to express the attitude of the atoms towards each other which becomes so conspicuous in these cases under the influence of sunlight. It seems to me that this phenomenon is a clear justification of our hylozoic monism when it affirms that all matter is psychic. In metaphysics sensation is held to be an essential property of the soul.

In the same general way as light the heat-stimulus acts on organisms, and causes the sensations, sometimes pleasant and sometimes unpleasant, which we call the subjective feeling of heat, warmth, coolness, or cold. The sense-organ that receives these impressions of temperature is the surface of the unicellular plasmic body in the protists, and the skin (epidermis) that protects the surface from the outer world in the histona. In all living things the temperature of the surrounding medium (water or air) has a great influence in regulating the life-processes; in the stationary animals and plants it is the temperature of the ground to which they are attached. This temperature must always be between the freezing-point and boiling-point of water, as fluid water is indispensable for the imbibition of the living matter and the molecular movements within the plasm. At the same time, some of the lower protists (chromacea, bacteria) can endure very high and very low temperatures, but only for a short time. Some protists (monera and diatomes) can stand a temperature of 200° C. for several days, and others can be heated above boiling-point without being killed. Arctic and High-Alpine plants and animals may be in a frozen condition for several months, yet live again when they are thawed. However, the resistance to these extremes of cold lasts for only a limited time, and in the frozen state all vital functions are at a standstill.

In the great majority of living things the vital activity is confined within narrow limits of temperature. Many plants and animals in the tropics which have been accustomed for thousands of years to the constancy of the hot equatorial climate can endure only very restricted variations of temperature. On the other hand, many of the inhabitants of Central Siberia, where the climate is very hot in the short summer and very cold in the long winter, can stand great variations. Thus the living plasm has experienced considerable changes in its sense of warmth through adaptation to different environments; not only the maximum and the minimum, but the optimum (most agreeable point), is subject to very great variations. This can easily be observed and followed experimentally in the phenomena of thermotaxis or thermotropism--that is to say, the effect that follows from a one-sided action of the heat-stimulus. The organism that falls below the minimum of temperature is said to be stiff with cold, while the organism that rises above the maximum is stiff with heat.

The heat-stimulus acts on inorganic as well as organic bodies, like the light-stimulus. The law holds good in both cases that higher temperatures increase sensation, while lower ones paralyze it. There is a minimum, an optimum, and a maximum, for many chemical and physical processes in the inorganic world. As far as the melting effect of water is concerned, freezing is the minimum of the heat stimulus and boiling the maximum. As the various chemical compounds meet in water at very different temperatures, we have an optimum for many substances--that is to say, a degree of warmth which is most favorable to the solution of a given quantity of a solid body in water. On the whole, the law holds for chemical processes that they are accelerated by high temperatures and retarded by low ones (like the human passions!); the former have a stimulating and the latter a benumbing effect. As the action of the various chemical compounds on each other is determined by the nature of the elements and their affinities, we must trace the variations in their conduct towards thermic stimuli to a sensation of temperature in the constituent atoms; increase of temperature stimulates it, while decrease lessens or paralyzes it. Here, again, the simple inorganic processes have a general resemblance to the complicated vital phenomena in the organic body.

Since we regard the whole of organic life as, in the ultimate analysis, merely a very elaborate chemical process, we shall quite expect that chemical stimuli are the most important factors in sensation. And this is so in point of fact; from the simplest moneron up to the most highly differentiated cell and on to the flower in the plant and the mental life of man, the vital processes are dominated by chemical forces and conversions of energy, which are set in play by external or internal chemical stimuli. The excitation which they produce is called, in a general way, "sensation of matter" or chemæsthesis; the basis of it is the mutual relation of the chemical elements which we describe as chemical affinity. In this affinity we have the play of attractive forces which lie in the nature of the elements themselves, especially in the peculiar properties of their constituent atoms; and this cannot be explained unless we ascribe unconscious sensation (in the widest sense) to the atoms, an inherent feeling of pleasure and the reverse, which they experience in the contact of other atoms (the "loves and hatreds of the elements" of Empedocles).

The numbers of different stimuli that act chemically on the plasm and excite its "sensation of matter" may be divided into two groups--external and internal stimuli. The latter lie within the organism itself, and cause the internal "organic sensations"; the former are in the outer world, and are felt as taste, smell, sex-impulse, etc. In the higher animals special chemical sense-organs have been developed for these chemical stimuli. As these are well known to us from our own human experience, and comparative physiology shows us the same structures in the higher animals, we will deal first with them. In general the same law holds for these external chemical stimuli as for optical and thermic stimuli; we can recognize a maximum limit of their action, a minimum below which they fail to stimulate, and an optimum or stage in which their influence is strongest.

The important part played in human life by taste and the pleasure associated with it is well known. The careful choice and preparation of savory food--which has become an art in gastronomy and a branch of practical philosophy in gastrosophy--was just as important two thousand years ago with the Greeks and Romans as it is to-day in royal banquets or the Lucullic dinners of millionaires. The excitement that we see associated with this refined combination of rich foods and drinks, and that finds expression in so many speeches and toasts, has its philosophic root in the harmony of gustatory sensations and the varying play of stimuli that the delicate dishes and wines exercise on the organs of taste, the tongue and palate. The microscopic organs of these parts of the mouth are the gustatory papillæ--cup-shaped structures, covered with spindle-shaped "taste-cells," and having a narrow opening into the cavity of the mouth. When sapid matters, drinks and fluid or loose particles of food, touch the taste-cells, they excite the fine terminal branchlets of the gustatory nerve which enters the cells. As we find that there are similar structures in most of the higher animals, and that they also choose their food with some care, we may confidently assume that they have sensations of taste like man. However, no trace of this is found in many of the lower animals; in these cases it is impossible to lay down a line of demarcation between taste and smell.

In man and the higher air-breathing vertebrates the seat of the sense of smell is in the nostrils; in man it is especially that part of the mucous lining of the nasal cavity which we call the "olfactory region" (the uppermost part of the nasal dividing wall, the superior and middle meatus). It is necessary for a sensation of smell that the odorous matter, or olfactory stimuli, be brought in a finely divided condition over the moist olfactory membranes. When they touch the olfactory cells--slender, rod-shaped cells with very fine hairs at the free end--they excite the ends of the olfactory nerve which are connected with the cells.

In many animals, especially mammals, the sense of smell has a much more important part in life than it has in man, in whom it is relatively feeble. It is well known that dogs and other carnivora, and even ungulates, have a much keener smell. In these cases the nasal cavity, which is the seat of the sense, is much larger, and the muscles in it are much stronger. The nostrils of the air-breathing vertebrates have been developed from a pair of open nasal depressions in the skin of the fish's head. But in these aquatic vertebrates the chemical action of the olfactory stimuli must be of a different character, like the sensation of taste. The odorous matter is, in these cases, brought into contact with the olfactory membrane in a liquid form (in which condition it is not perceptible to man). In fact, the division between the senses of smell and taste disappears altogether in the lower animals. These two "chemical senses" are closely related, and have a common feature in the direct chemical action of the stimulus on the sensitive part of the skin.

A chemical sensation of matter that corresponds completely to the real taste-sensation in the higher animals is found in some of the higher carnivorous plants. The leaves of the sun-dew (_drosera rotundifolia_) are very sensitive insect-traps, and are armed at the edge with knob-like tentacles, sticky hairs that secrete an acid, flesh-digesting juice. When a solid body (but not a raindrop) touches the surface of the leaf the stimulus acts in such a way on the tentacle heads as to contract the leaf. But the acid fluid which serves for digestion, and corresponds to the gastric juice in the animal, is only secreted by the corpuscles if the solid foreign body is nitrogenous (flesh or cheese). Hence the leaves of these insectivorous plants taste their meat diet, and distinguish it from other solids, to which they are indifferent. In the broader sense, in fact, we may describe the points of the roots of plants as organs of taste; they plunge into the richer parts of the earth which yield more nourishment, and avoid the poor parts. In unicellular plants and animals the action of chemical stimuli is especially conspicuous when it is one-sided, and provokes definite movements in one particular direction (_chemotaxis_).

The movements of unicellular organisms that are provoked by chemical stimuli and are known as chemotropism (more recently as chemotaxis) are particularly interesting because they show the existence of a chemical sensitiveness, somewhat resembling taste or smell, in the lowest organisms, and even in the homogeneous plasm of the monera. Repeated experiments of Wilhelm Engelmann, Max Verworn, and others, have shown that many bacteria, diatomes, infusoria, rhizopods, and other protists, have a similar sense of taste; they move towards certain acids (for instance, a drop of malic acid) or a bubble of oxygen that lies on one side of the drop of water in which the protists are under the microscope. Many pathogenetic bacteria secrete poisonous substances which are very injurious to the human frame. The active white blood-cells, leucocytes, in the human blood have a special "taste" for these bacteria-poisons, and concentrate in large quantities, by means of their amœboid movements, at those parts of the body where they are secreted. If the leucocytes prove the stronger in their struggle with the bacteria, they destroy them, and in this way they act as sanitary officers in keeping poisonous infection out of our organism. But if the bacteria win the battle, they are transported into other parts of the body by the leucocytes; they distinguish their plasm by taste, and may cause a deadly infection.

We have a particularly interesting and important species of chemical irritation in the mutual attraction of the two sex-cells, to which I gave the name of chemotropism thirty years ago, and which I described as the earliest phylogenetic source of sexual love (see the _Anthropogeny_, chapters vii. and xxix.). The remarkable phenomena of impregnation, the most important of all the processes of sexual generation, consist in the coalescence of the female ovum and the male sperm-cell. This could not take place if the two cells had not a sensation of their respective chemical constitution and disposition for union; they come together under this impulse. This sexual affinity is found at the lowest stages of plant life, in the protophyta and algæ. With these both cells--the smaller male microgameta and the larger female macrogameta--are often mobile, and swim about in order to effect a union. In the higher plants and animals only the small male cell is mobile as a rule, and swims towards the large immobile ovum in order to blend with it. The sensation that impels it is of a chemical nature, allied to taste and smell. This has been proved by the splendid experiments of Pfeffer, who showed that the male ciliated cells of ferns are attracted by malic acid, and those of the mosses by cane-sugar, just in the same way as by the exhalation from the female ovum. Conception depends on exactly the same erotic chemotropism in the fertilization of all the higher organisms.

Erotic chemotropism must be regarded as a general sense-function of the sexual cells in all amphigonous organisms, but in the higher organisms special forms of the sex-sense, connected with specific organs, are developed; as the source of sexual love they play a most important part in the life of many of the histona. In man and most of the higher animals these feelings of love are associated with the highest features of psychic life, and have led to the formation of some most remarkable customs, instincts, and passions. Wilhelm Bölsche has given us an admirable selection from this infinitely rich and attractive realm in his famous _Life of Love in Nature_ (1903). It is well known that this sexual sense as we have it in man has been developed from the nearest related mammals, the apes. But while it offers a shameless and repulsive spectacle in many of the apes, it has been greatly ennobled and refined in man in the development of civilization. However, the sexual sense-organs and their specific energy have remained the same. In the vertebrates and the articulates and many other metazoa the copulative organs are equipped with special cell-forms (voluptuous particles), which are the seat of intensely pleasurable feelings (see the _Anthropogeny_, chapter xxix., plate 30). The pubic hairs which clothe the _mons Veneris_ are also delicate organs of the sex-sense, and so are the tactile hairs about the mouth. In these cases the correlation between the sensitive forms of energy in the copulative organs and the psychic functions of the central nervous system has been remarkably developed. Moreover, a large part of the rest of the skin may co-operate as a secondary organ of the sex-sense, as is seen in the effect of caressing, stroking, embracing, kissing, etc. Goethe, at once the greatest lyric poet and the subtlest and profoundest monistic philosopher of Germany, has given unrivalled expression to this sensual, yet supersensual, basis of sexual love. Ontogeny teaches unmistakably that its elementary organs, the epidermic cells, develop entirely from the ectoderm.

By "organic sensations" modern physiology understands the perception of certain internal bodily states, which are mostly brought about by chemical stimuli (to a small extent by mechanical and other irritation) in the organs themselves. As subjective feelings of the organism itself these states are most aptly called "feelings"--the positive states, pleasure, comfort, delight; the negative, discomfort, pain, etc. These organic sensations (also called common sensations or feelings) are of great importance for the self-regulation of the complicated organism. To the positive organic sensations belong not only the bodily feeling of satiety, repose, or comfort, but also the psychic feelings of joy, good humor, mental rest, etc. Among negative common feelings we have not only hunger and thirst, bodily fatigue, bodily pain, sea-sickness, etc., but also mental strain, vertigo, bad humor, and so on. Between the two groups we have the third category of neutral organic sensations, which involve neither pleasure nor pain, but merely the perception of certain internal conditions, such as muscular strain (in lifting heavy objects), the disposal of the limbs (in crossing the legs), and so on.

Chemical sensation is just as general and important in organic nature as in the life of organisms. In this case it is nothing less than the basis of chemical affinity. No chemical process can be thoroughly understood unless we attribute a mutual sensation to the atoms, and explain their combination as due to a feeling of pleasure and their separation to a feeling of displeasure. The great Empedocles (fifth century B.C.) explained the origin of all things long ago by the various combination of pure elements, the interaction of love (attraction) and hate (repulsion). This attraction or repulsion is, of course, unconscious, just as in the instincts of plants and animals. If one prefers to avoid the term "sensation," it may be called "feeling" (_æsthesis_), while the (involuntary) movement it provokes may be called "inclination" (_tropesis_), and the capacity for the latter "tropism" (more recently _taxis_, _cf._ chapter xii. of the _Riddle_). We may illustrate it from the simplest case of chemical combination. When we rub together sulphur and mercury, two totally different elements, the atoms of the finely divided matter combine and form a third and different chemical body, cinnabar. How would this simple synthesis be possible unless the two elements _feel_ each other, move towards each other, and _then_ unite?

We find universally distributed in nature the sensation of the mechanical stimulus of gravitation, the most comprehensive statement of which is given in Newton's law of gravity. According to this fundamental and all-ruling law, any two particles of matter are attracted in direct proportion to their mass and inverse proportion to the square of their distance. This form of attraction, also, can be traced to a "sensation of matter" in the mutually attracting atoms. The local sensation that any body provokes by contact with the surface of an organism is felt as pressure (_baros_). A stimulus that causes this pressure alone brings about a counter-pressure as a reaction, and an effort to neutralize it, the pressure-movement (_barotaxis_ or _barotropism_). Sensitiveness to pressure or the contact of solid bodies is found throughout the organic world; it can be proved experimentally among the protists as well as the histona. Special sense-organs have been developed in the skin of the higher animals as the instruments of this pressure-sense (baræsthesis) in the form of tactile corpuscles; they are most numerous at the finger-tips and other particularly sensitive parts. In many of the higher animals there is a fine sense of touch in the feelers or tentacles, or (in the higher articulates) in the horns or antennæ. Moreover, these tactile and prehensile organs are also very widely found among the higher plants, especially the climbing plants (vines, bryony, etc.). Their slender creepers, which roll out spirally, have a very delicate feeling for the nature of the supports which they embrace; they distinguish between smooth and rough, thick and thin supports, and prefer the latter. Many of the higher plants, which are particularly sensitive to pressure, have, to an extent, special organs of touch (tentacles), and reveal this by the movements of their leaves (the sensitive plants, _mimosa_, _dionæa_, _oxalis_). But even among the unicellular protists we find that the contact of solid bodies has an irritating effect, the perception of which provokes corresponding movements (_thigmotaxis_ or _thigmotropismus_). A peculiar form of pressure-sensation is produced in many organisms by the flow of liquids; in the mycetozoa, for instance, it provokes counter-movements (_rheotaxis_, _rheotropismus_), as Ernst Strahl showed by his experiments on _æthelium septicum_.

We have an interesting analogy to the thigmotaxis of the viscous living plasm in the elasticity of solid inorganic bodies, such as an elastic steel-rod. In virtue of its springy nature, the elastic rod reacts on the pressure of force that has bent it, and endeavors to regain its former position. The spiral spring sets the works of the clock in motion in virtue of its elasticity.

A very important part is played in botany by the action of gravitation on the growth of plants. The attraction towards the centre of the earth causes the positively geotropic roots to grow vertically into the earth, while the negatively geotropic stalk pushes out in the opposite direction. This applies also to a number of stationary animals which are attached to the ground by roots, such as polyps, corals, bryozoa, etc. And even the locomotion of free animals, the disposition of their bodies to the ground, the position and posture of their limbs, etc., is determined partly by the feeling of gravitation, and partly by adaptation to certain functions which resist this, as in running, swimming, and so on. All these geotropic sensations belong to the same group of barotactile phenomena, as the fall of a stone or any other effect of gravitation that depends on an inorganic feeling of attraction.

As a result of these adaptations, we find a distinct sense of space developed in the higher, free-moving animals. The feeling of the three dimensions of space becomes an important means of orientation, and in the vertebrates, from the fishes up to man, the three spiral canals in the inner ear are developed as special organs of this. These three semicircular canals, which lie vertically to each other in the three dimensions of space, are the organs of the sensation that guides the movements of the head, and, in relation to this, for the normal posture of the body and the feeling of equilibrium. If the three spiral canals are destroyed, the equilibrium is lost; the body totters and falls. Hence, these organs are not of an acoustic, but a static or geotactic character; and the same may be said of the so-called "auditory vesicles" of many of the lower animals--round vesicles which contain a liquid and a solid body, the otolith. When this body changes its position with the change of posture of the whole frame, it presses on the fine auditory hairs, or delicate terminations of the auscultory nerve, which enters the vesicle. In fact, the sense of equilibrium is often combined with the sense of hearing.

The perception of noises and tones, which we call hearing, is restricted to a section of the higher, free-moving animals; if, that is to say, the above-mentioned "auditory vesicles" in the lower animals do not have acoustic as well as static sensations. The specific sensation of hearing is due to vibration of the medium in which the animal lives (air or water), or to vibrations of solid bodies (such as tuning-forks) which are brought into touch with them. If the vibrations are irregular, they are felt as "noises"; if regular, they are heard as "tones" or notes; when a number of tones together (fundamental and over-tones) excite a complex sensation, we have "timbre." The vibrations of the sounding body are borne to the auditory cells, which represent the terminal extensions of the auscultory nerve. The specific sensation of hearing can, therefore, be traced originally to the sense of pressure, from which it has been evolved. As the organ of hearing is, like the eye, one of the principal instruments of the higher mental life, and as the refined musical hearing of civilized man is often taken to be a metaphysical power of the soul, it is important to note that here again the starting-point was purely physical--that is to say, it can be traced to the sense of pressure of matter, or gravitation.

The great importance of electricity as an agency in nature, both organic and inorganic, has only lately been fully appreciated. Electric changes are connected with many (if not, as is now supposed, with all) chemical and optical processes. Man himself and most of the higher animals have no electric organs (apart from the eye), and no sense-organs that experience a specific electric sensation. It is probably otherwise with many of the lower animals, especially those that develop free electricity, such as the electric fishes. The larvæ of frogs and embryos of fishes, if put in a vessel of water through which a galvanic current is sent, place themselves when it is closed with their longitudinal axis in the direction of the current, with the head directed to the anode and the tail to the cathode (Hermann). Again, the luminous sea-animals which cause the beautiful phenomenon of the illumination of the sea, and the glow-worms and other luminous organisms, have probably an unconscious feeling of the flow of electric energy associated with these phenomena. Many plants show a direct reaction to electric stimuli; when, for instance, we send a constant galvanic current for some time through the points of their roots (very sensitive organs, compared by Darwin to the brain of the animal), they bend towards the cathode.

Many of the protists are very sensitive to electric currents, as Max Verworn especially proved by a series of beautiful experiments. Most of the ciliated infusoria and many of the rhizopods (_amœba_) are cathodically sensitive or negatively galvanotactic. When we send a constant electric current through a drop of water in which thousands of _paramœcium_ are moving about, all the infusoria swim at once, with the anterior pole of the body foremost, towards the cathode or negative pole; they accumulate about it in great crowds. If the direction of the current is now changed, the whole swarm at once make in the opposite direction for the new cathode. Most of the flagellate infusoria do just the reverse; they are anodically sensitive or positively galvanotactic. In a drop of water, in which swarms of _polytoma_ are moving about, all the cells swim at once towards the anode or positive pole, when an electric current is sent through. The opposite galvanotropic behavior of these two groups of infusoria in a drop of water, in which they are mixed together, is very interesting; as soon as a constant stream enters it, the ciliata fly to the cathode and the flagellata to the anode. When the current is reversed the two swarms rush at each other like hostile armies, cross in the middle of the drop, and gather at the opposite poles. These and other phenomena of galvanic sensation show clearly that the living plasm is subject to the same physical laws as the water that is decomposed into hydrogen and oxygen by an electric current. Both elements _feel_ the opposite electricities.

SCALE OF SENSATION AND IRRITABILITY

1st Stage: SENSATION OF ATOMS. Affinity of the elements in every chemical combination.

2d Stage: SENSATION OF MOLECULES (groups of atoms): in the attraction and repulsion of molecules (positive and negative electricity, etc.).

3d Stage: SENSATION OF PLASTIDULES (micella, biogens, or plasma-molecules): in the simplest vital process of the monera (chromacea and bacteria).

4th Stage: SENSATION OF CELLS: irritability of the unicellular protists (protophyta and protozoa): erotic chemotropism connected with the nucleus and trophic with the cell-body.

5th Stage: SENSATION OF CŒNOBIA (volvox, magosphæra). With the formation of cell-communities we have association of sensations (individual feeling on the part of the social cells together with common feeling on the part of the community).

6th Stage: SENSATION OF THE LOWER PLANTS. In the metaphyta or tissue-plants all the cells are still equally sensitive at the lower stages: there are no special sense-organs.

7th Stage: SENSATION OF THE HIGHER PLANTS. In the higher metaphyta specially sensitive cells, or groups of cells, with a specific energy, are developed at certain points: sense-organs.

8th Stage: SENSATION OF THE LOWER METAZOA, without differentiated nerves or sense-organs. Lower cœlenteria: sponges, polyps, platodaria.

9th Stage: SENSATION OF THE HIGHER METAZOA, with differentiated nerves and sense-organs, but still without consciousness(?). The higher cœlenteria and most of the cœlomaria.

10th Stage: SENSATION WITH DAWNING CONSCIOUSNESS, with independent formation of the phronema. The higher articulata (spiders and insects) and vertebrates (amphibia, lower reptiles, lower mammals).

11th Stage: SENSATION WITH CONSCIOUSNESS AND THOUGHT: amniotes: higher reptiles, birds, and mammals: savages.

12th Stage: SENSATION WITH PRODUCTIVE MENTAL ACTION IN ART AND SCIENCE: civilized men.

XIV

MENTAL LIFE

Mind and soul--Intelligence and reason--Pure reason--Kant's dualism--Anthropology--Anthropogeny--Embryology of the mind--Mind of the embryo--The canonical mind--Legal rights of the embryo--Phylogeny of the mind--Paleontology of the mind--Psyche and phronema--Mental energy--Diseases of the mind--Mental powers--Conscious and unconscious mental life--Monistic and dualistic theory--Mental life of the mammals, of savages, and of civilized and educated people.

The greatest and most commanding of all the wonders of life is unquestionably the mind of man. That function of the human organism, to which we give the name of "mind," is not only the chief source of all the higher enjoyment of life for ourselves, but it is also the power that most effectually separates man from the brute according to conventional beliefs. Hence it is supremely important for our biological philosophy to devote a few careful pages to the study of its nature, its origin and development, and its relation to the body.

At the very outset of our psychological inquiry we are met by the difficulty of giving a clear definition of "mind," and distinguishing it from "soul." Both ideas are extremely ambiguous: their content and connotation are described in the most various ways by the representatives of science. Generally speaking, we mean by mind that part of the life of the soul which is connected with consciousness and thought, and is, therefore, only found in the higher animals which have intelligence and reason. In a narrower sense reason is regarded as the proper function of mind, and as the essential prerogative of man in the animal world. In this sense Kant especially has done much to strengthen the prevailing conception of mental action, and has, by his _Critique of Pure Reason_, converted philosophy into a mere "science of reason." In consequence of this conception, which still prevails widely in scientific circles, we will first study the mental life in the action of reason, and try to form a clear idea of this great wonder of life.

Psychologists and metaphysicians are of very varied opinions as to the difference between intelligence and reason. Schopenhauer, for instance, considers causality to be the sole function of intelligence, and the formation of concepts to be the province of reason; in his opinion the latter power alone marks off man from the brute. However, the power of abstraction, which collects the common features in a number of different presentations, is also found in the higher animals. Intelligent dogs not only discriminate between individual men, cats, etc., according as they are sympathetic or the reverse, but they have a general idea of man or cat, and behave very differently towards the two. On the other hand, the power of forming concepts is still so slight in uncivilized races that it rises but little above the mind of dogs, horses, etc.; the mental interval between them and civilized man is extremely wide. However, a long scale of reason unites the various stages of association of presentations which lead up to the formation of concepts; it is quite impossible to lay down a strict line of demarcation between the lower and higher mental functions of animals, or between the latter and reason. Hence the distinction between the two cerebral functions is only relative; the intelligence comprises the narrower circle of concrete and more proximate associations, while reason deals with the wider sphere of abstract and more comprehensive groups of association. In the scientific life of the mind, therefore, the intelligence is always occupied with empirical investigation, and reason with speculative knowledge. But the two faculties are equally functions of the phronema, and depend on the normal anatomic and chemical condition of this organ of thought.

Since Kant won so great a prominence in modern philosophy for the idea of pure reason by his famous _Critique_ (1781), it has been much discussed, especially in the modern metaphysical theory of knowledge. It has, however, like all other ideas, undergone considerable changes of meaning in the course of time. Kant himself at first understood by pure reason "reason independent of all experience." But impartial modern psychology based on the physiology of the brain and the phylogeny of its functions, has shown that there is no such thing as this pure _a priori_ knowledge, independent of all experience. Those principles of reason which at present seem to be a priori in this sense have been attained in virtue of thousands of experiences. In so far as this is a question of real knowledge of the truth, Kant himself has frequently recognized the point. He says expressly in his _Prolegomena to any future metaphysic that can be regarded as Science_ (1783, p. 204): "A knowledge of things by pure reason or pure intelligence is nothing but an empty appearance; only in experience is there truth." In subscribing to this empirical theory of knowledge of Kant I. and rejecting the transcendental theory of Kant II., we may on our side understand by pure reason "knowledge without prejudices," free from all dogma--all fictions of faith.

The familiar cry of modern metaphysicians, "Return to Kant," has become so general in Germany that not only nearly all metaphysicians--the official representatives of "philosophy" at our universities--but also many distinguished scientists, regard Kant's dualistic theory of knowledge as a necessary condition for the attainment of truth. Kant dominated philosophy in the nineteenth century much as Aristotle did in the Middle Ages. His authority became especially powerful when the prevailing Christian faith believed that his "practical reason" fully supported its own three fundamental dogmas--the personality of God, the immortality of the soul, and the freedom of the will. It overlooked the fact that Kant had utterly failed to find proofs of these dogmas in his _Critique of Pure Reason_. Even conservative governments found favorable features in this dualistic philosophy. We are, therefore, forced to return once more to this mischievous system; though Kant's antinomy of the two reasons has now been refuted so often and so thoroughly that we need not dwell any further on this point.

Although the great Königsberg philosopher brought every side of human life within his comprehensive sphere of study, man remained to him--as he had been to Plato and Aristotle, Christ and Descartes--a dual being, made up of a physical body and a transcendental mind or spirit. Comparative anatomy and evolution, which have provided the solid morphological basis of monistic anthropology, did not come into existence until the beginning of the nineteenth century; they were quite unknown to Kant. He had, however, a presentiment of their importance, as Fritz Schultze has shown in his interesting work on _Kant and Darwin_ (1875). We find in various places expressions which may be described as anticipations of Darwinism. Kant also gave lectures on "Pragmatic Anthropology," and studied the psychology of races and peoples. It is remarkable that he did not arrive at a phylogenetic conception of the human mind, and a recognition of the possibility of its evolution from the mind of other vertebrates. It is clear that he was held back from this by the profound mystic tendency of his theory of reason, and the dogma of the immortality of the soul, the freedom of the will, and the categorical imperative. Reason remained in Kant's view a transcendental phenomenon, and this dualistic error had a great influence on the whole structure of his philosophy. It must be remembered, of course, that our knowledge of the psychology of peoples was then very imperfect; but a critical study of the facts then known should have sufficed to convince him of the lower and animal condition of their minds. If Kant had had children, and followed patiently the development of the child's soul (as Preyer did a century later), he would hardly have persisted in his erroneous idea that reason, with its power of attaining _a priori_ knowledge, is a transcendental and supernatural wonder of life, or a unique gift to man from Heaven.

The root of the error is that Kant had no idea of the natural evolution of the mind. He did not employ the comparative and genetic methods to which we owe the chief scientific achievements of the last half-century. Kant and his followers, who confined themselves almost exclusively to the introspective method or the self-observation of their own mind, regarded as the model of the human soul the highly developed and versatile mind of the philosopher, and disregarded altogether the lower stages of mental life which we find in the child and the savage.

The immense advance made by the science of man in the second half of the nineteenth century cut the ground from under the older anthropology and the dualistic system of Kant. A number of newly founded branches of science co-operated in the work. Comparative anatomy showed that our whole complicated frame resembles that of the other mammals, and in particular differs only by slight stages of growth, and therefore in the details of the organs, from that of the anthropoid apes. The comparative histology of the brain especially showed that this is also true of the brain, the real organ of mind. From comparative embryology we learned that man develops from a simple ovum just like the anthropoid ape; in fact, that it is almost impossible to distinguish between the ape and the human embryo even at a late stage of development. Comparative animal chemistry explained that the chemical compounds which build up our organs, and the conversions of energy which accompany its metabolism, resemble those in the other vertebrates. Comparative physiology taught us that all man's vital functions--nutrition and reproduction, movement and sensation--can be traced to the same physical laws in man as in all the other vertebrates. Above all, the comparative and experimental study of the sense-organs and the various parts of the brain showed that these organs of the mind work in the same way in man as in the other primates. Modern paleontology taught that man is, it is true, more than a hundred thousand years old, but only appeared on earth towards the close of the Tertiary Period. Prehistoric research and comparative ethnology have shown that civilized nations were preceded by older and lower races, and these by savages, which have a close bodily and mental affinity to the apes. Finally, the reformed theory of descent (1859) enabled us to unite the chief results of the various branches of anthropological study, and explain them phylogenetically by the development of man from other primates (anthropoid apes, cynocephali, lemures, etc.). By this means a new and monistic basis was provided for modern anthropology; the position assigned to man in nature by dualistic metaphysics was shown to be utterly untenable. I have attempted in the last edition of my _Anthropogeny_ (of which an English edition is in preparation) to combine all these results of empirical investigation in a sketch of the natural evolution of man, paying special regard to embryology. I pointed out in chapters ii.-vi. of the _Riddle_ how important a part of our monistic philosophy this phylogenetic anthropology is.

The monistic conception of the human body and mind, which the theory of descent has put on a zoological basis, was bound to meet with the sternest resistance in dualistic and metaphysical circles. It was, however, also regarded with great disapproval by many modern empirical anthropologists, especially those who take it to be their chief task to make as "exact" a study as possible of the human frame, and measure and describe its various parts. We might have expected these descriptive anthropologists and ethnologists to extend a friendly hand to the new anthropogeny, and avail themselves of its leading ideas, in order to bring unity and causal connection into the enormous mass of empirical material accumulated. However, this took place only to a limited extent, The majority of anthropologists regarded evolution, and especially the evolution of man, as an undemonstrated hypothesis. They confined themselves to accumulating huge masses of raw empirical material, without having any clear aim or any definite questions in view. This was chiefly the case in Germany, where the Society of Anthropology and Prehistoric Research was for thirty years under the lead of Rudolph Virchow. This famous scientist had won great honor in connection with the reform of medicine by his cellular pathology and a number of distinguished works on pathological anatomy and histology since the middle of the nineteenth century. But when he afterwards (subsequently to his removal to Berlin, 1856) devoted himself chiefly to political and social questions, he lost sight of the great advance made in other branches of biology. He completely failed to appreciate its greatest achievement--the establishment of the science of evolution by Darwin. To this we must add the psychological metamorphosis (similar to that of Wundt, Baer, Dubois-Reymond, and others), of which I have spoken in the sixth chapter of the _Riddle_. The extraordinary authority of Virchow, and the indefatigable zeal with which he struggled every year until his death (1903) against the descent of man from other vertebrates, caused a wide-spread opposition to the doctrine of evolution. This was supported especially by Johannes Ranke, of Munich, the secretary of the Anthropological Society. Happily, a change has recently set in. However, my _Anthropogeny_ has remained for thirty years the only work of its kind--namely, a comprehensive treatment of man's ancestral history, especially in the light of embryology.

As I pointed out in the eighth and ninth chapters of the _Riddle_, the most solid foundation of our monistic psychology is the fact that the human mind grows. Like every other function of our organism, our mental activity exhibits the phenomenon of development in two directions, individually in each human being and phyletically in the whole race. The ontogeny of the mind--or the embryology of the human soul--brings before us in direct observation the various stages of development through which the mind of every man passes from the beginning to the close of life. The phylogeny of the mind--or the ancestral history of the human soul--does not afford us this direct observation; it can only be deduced by a comparison and synthesis of the historical indications which are supplied by history and prehistoric research on the one hand, and the critical study of the various stages of mental life in savages and the higher vertebrates on the other. In this the biogenetic law is used with great success (chapter xvi.).

As everybody knows, the new-born child shows as yet no trace of mind or reason or consciousness; these functions are wanting in it as completely as in the embryo from which it has been developed during the nine months in the mother's womb. Even in the ninth month, when most of the organs of the human embryo are formed and arranged as they appear later, there is no more trace of mind in its psychic life than in the ovum and spermatozoon from which it was evolved. The moment in which these sexual cells unite marks precisely the real commencement of individual existence, and therefore of the soul also (as a potential function of the plasm). But the mind proper--or reason, the higher conscious function of the soul--only develops, slowly and gradually, long after birth. As Flechsig has shown anatomically, the cortex in the new-born child is not yet organized or capable of functioning. Rational consciousness is even impossible for the child when it begins to speak; it reveals itself for the first time (after the first year) at the moment when the child speaks of itself, not in the-third person, but as "I." With this self-consciousness comes also the antithesis of the individual to the outer world, or world-consciousness. This is the real beginning of mental life.

In defining the appearance of the individual mind by the awakening of self-consciousness, we make it possible to distinguish, from the monistic physiological point of view, between "soul" (_psyche_) and "spirit" (_pneuma_). There is a soul even in the maternal ovum and the paternal spermatozoon (_cf._ chapter xi.); there is an individual soul in the stem-cell (_cytula_) which arises at conception by the blending of the parent cells. But the mind proper, the thinking reason, develops out of the animal intelligence (or earlier instincts) of the child only with the consciousness of its personality as opposed to the outer world. At the same time the child reaches the higher stage of personality, which law has for a long time taken under its protection and made morally responsible to society by education. This shows how erroneous and untenable, from the physiological point of view, are the ideas still embodied in our code as to the psychic life and the mind of the embryo and the new-born infant. They came mostly from the canon law of the Catholic Church.

The dualistic ideas of the soul of the human embryo which were taught by the Church in the Middle Ages are particularly interesting from the psychological point of view; and at the same time they are of great practical importance even in our own day, since many of their moral consequences form an important element in canon law, and have passed from this into civil law. This influential canon law was formed under ecclesiastical authority from the decisions of Church councils and the decretals of the popes. It is, like most of the dogmas and decrees which civilization owes to this powerful hierarchy, a curious tissue of old traditions and new fictions, political dogmas, and crass superstition. It is directed to the despotic ruling of the uneducated masses and the exclusive dominion of the Church--a Church that calls itself Christian while thus acting as the very reverse of pure Christianity. The canon law takes its name from the dogmatic rules (or canons) of the Church. They involuntarily suggest the metal tubes which are so often the _ultima ratio regis_ in the wars of Christian nations. The canonical regulations of the Church, as implements of a crude spiritual despotism, have no more to do with the ethical laws of pure reason than the cannons of secular authorities have as naked organs of physical force. We might write the motto, _Ultima ratio ecclesiæ_ (the last argument of the Church), over the sacred _Corpus Juris Canonici_. A collection of later papal decretals which forms an appendix to the books of canon law was very happily given the official title of _Extravagantes_. Among the "extravagant" nonsense which the papacy included in canon law as a moral code for believers is its view of the psychic life of the embryo. The "immortal soul" is supposed to enter the soulless embryo only several weeks after conception. As theologians and metaphysicians are very much divided as to the period of this entrance of the soul, and know nothing about the structure of the embryo and its development, we will only recall the fact that the human fœtus cannot be distinguished from that of the anthropoid ape and other mammals even in the sixth week of its development. The outline of the five cerebral vesicles and the three higher sense-organs (nose, eye, and ear vesicle) is discernible in the head; the two pairs of limbs can be traced in the shape of four simple roundish unjointed plates; and the pointed tail sticks out at the lower part, the rudimentary legacy from our long-tailed ape-ancestors. Although the cortex is not yet developed at this stage, the embryo may be considered to have a "soul" (_cf._ chapters xiv. and xv. of my _Anthropogeny_, and plates 8-14).

It is said to be a great merit of canon law that it was the first to extend legal protection to the human embryo, and punished abortion with death as a mortal sin. But as this mystical theory of the entrance of the soul is now scientifically untenable, we should expect them consistently to extend this protection to the fœtus in its earlier stages, if not to the ovum itself. The ovary of a mature maid contains about 70,000 ova; each of these might be developed into a human being under favorable circumstances if it united with a male spermium after its release from the ovary. If the state is so eager for the multiplication of its citizens in the general interest, and regards prolific reproduction as a "duty" of its members, this is certainly a "sin of omission." It punishes abortion with several years' imprisonment. But while civil law thus takes its inspiration from canon law, it overlooks the physiological fact that the ovum is a part of the mother's body over which she has full right of control; and that the embryo that develops from it, as well as the new-born child, is quite unconscious, or is a purely "reflex machine," like any other vertebrate. There is no mind in it as yet; it only appears after the first year, when its organ, the phronema in the cortex, is differentiated. This interesting fact is explained by the biogenetic law, which shows that the ontogeny of the brain is a condensed recapitulation of its phylogeny in virtue of the laws of heredity.

The biogenetic law applies just as much to the brain, the organ of mind, as to any other organ of the human body. On the strength of the ontogenetic facts, which fall under direct observation, we infer that there was a corresponding development in the phylogenetic series of our animal ancestors. A significant confirmation of this inference is found in comparative anatomy. It shows that in all the skull-animals (_craniota_)--from the fishes and amphibia up to the apes and man--the brain is developed in the same way, as a vesicular distension of the ectodermal medullary tube. This simple oval cerebral vesicle first divides into three and afterwards five successive vesicles by transverse constriction (_Anthropogeny_, chapter xxiv., plate 24). It is the first of these vesicles, the cerebrum, that afterwards becomes the chemical laboratory of the mind. In the lower craniota (fishes and amphibia) the cerebrum remains very small and simple. It only reaches a notably higher stage in the three chief classes of the vertebrates, the amniotes. As these land-dwelling and air-breathing craniota have more difficult work to do in the struggle for life than their lower aquatic ancestors, we find much more varied and complex habits among them. These hereditary habits are gradually converted into instincts by functional adaptation and progressive heredity; and with the further development of consciousness in the higher mammals we have at last the appearance of reason. The gradual unfolding of the mental life is accompanied step by step with the advance of its anatomic organ, the phronema in the cortex. Recent careful investigations of the ontogeny and histology of the origin of mind (by Flechsig, Hitzig, Edinger, Ziehen, Oscar Vogt, etc.) have given us an interesting insight into the mysterious processes of its phylogeny.

While the comparative anatomy of the cortex gives us a good idea of the gradual historical development of the mind in the higher classes of vertebrates, we get at the same time from their fossilized remains positive indications as to the period of time in which this phylogenesis has slowly taken place. The historical series in which the classes of vertebrates have succeeded each other in the great periods of the organic history of the earth is directly demonstrated by their fossil remains--the real commemorative medals of natural creation--and gives us a most valuable record of the ancestral history of our race and of the mind. The oldest strata that contain vertebrate remains form the huge Silurian System, which were, on the latest calculations, formed more than a hundred million years ago. They contain a few fossil fishes. In the succeeding Devonian System these are followed by the dipneusta, transitional forms between the fishes and the amphibia. The latter, the oldest four-footed and five-toed vertebrates, appear in the Carboniferous Period. They are succeeded in the Permian, the next system, by the oldest amniotes, the primitive reptiles (tocosauria). It is not until the next period (the Triassic) that the oldest mammals are found, small primitive monotremes (_pantotheria_), then marsupials in the Jurassic, and the first placentals in the Cretaceans. The great wealth of varied and highly organized forms which are contained in this third and last sub-class of the mammals appear only in the succeeding Tertiary Period. The numbers of well-preserved skulls which these placentals have left behind in fossil form are particularly important, because they give us an idea of the quantitative and qualitative formation of the brain within the various orders; thus, for instance, in the modern carnivora the brain is from two to four times, and in the modern ungulates from six to eight times, as large (in proportion to the size of the body) as in their earliest Tertiary ancestors. It is also found that the cortex (the real organ of mind) has developed in the Tertiary Period at the expense of the other parts of the brain. The duration of this Cænozoic Period has lately been calculated at three million years (according to other geologists twelve to fourteen or more million years). It was, at all events, sufficient to make possible the gradual development of the human mind from the lower intelligence of our ape-ancestors and the instincts of the older placentalia.

We have given the physiological name of the "phronema," as the real organ of mind or the instrument of reason, to that part of the cortex on the normal anatomic condition of which the action of the human mind depends. The remarkable investigations during the last few decades of the finer texture of the grey cortex (or cortical substance of the cerebrum) have shown that its structure--a real anatomic "wonder of life"--represents the most perfect morphological product of plasm; and its physiological function--mind--is the most perfect action of a "dynamo-machine," the highest achievement that we know anywhere in nature. Millions of psychic cells or neurona--each of them of an extremely elaborate fibril molecular structure--are associated as special thought-organs (phroneta) at certain parts of the cortex, and these again are built up into a large harmonious system of wonderful regularity and capacity. Each phronetal cell is a small chemical laboratory, contributing its share to the unified central function of the mind, the conscious action of reason. Scientists are still very far from agreement as to the extent of the phronema in the cortex and its delimitation from the neighboring sense-centres (sensoria). But they are all agreed that there is such a central organ of mind, and that its normal anatomic and chemical condition is the first requisite for the life of the human mind. This belief--one of the foundations of monistic psychology--is confirmed by the study of psychiatry.

The study of the diseased organism has greatly furthered our knowledge of the normal frame. Diseases are so many physiological experiments made by nature herself under special conditions, which experimental physiology would often be unable to arrange artificially. The thoughtful physician or pathologist can often obtain most important knowledge of the function of organs by carefully observing them during disease. This is especially true of diseases of the mind, which always have their immediate foundation in an anatomical or chemical modification of certain parts of the brain. Our advancing knowledge of the localization of mental functions, or of their connection with special phroneta or organs of thought, is for the most part based on the experience that the destruction of the one is followed by the extinction of the other. Modern psychiatry, the empirical science of mental disease, has thus become an important element of our monistic psychology. If Immanuel Kant had studied it and had visited the asylum wards for a few months, he would certainly have escaped the dualist errors of his philosophy. We may say the same of the modern metaphysical psychologists who built up a mystic theory of an immortal soul without knowing the anatomy, physiology, and pathology of the brain.

The comparative anatomy, physiology, and pathology of the brain, in concurrence with the results of ontogeny and phylogeny, have led us to form the sound monistic principle that the human mind is a function of the phronema, and that the neurona of the latter, or the phronetal cells, are the real elementary organs of mental life. Hence modern energism is perfectly justified in regarding mental energy (in all its forms) from the same point of view as all other forms of nervous energy, and in fact all manifestations of energy in organic or inorganic nature. Fechner's psychophysics had already shown that a part of this nervous energy is measurable and mathematically reducible to the mechanical laws of physics (_Riddle_, chapter vi.) Ostwald has, in his _Natural Philosophy_, lately emphasized the fact that all the manifestations of mental life, not only sensation and will, but even thought and consciousness, can be reduced to nervous energy. Hence we may distinguish what are called mental forces from the other expressions of nervous energy as _phronetic energy_. The monistic research of Ostwald on the energy-processes in mental life (chapter xviii.), consciousness (chapter xix.), and will (chapter xx.) is very notable, and confirms the views I advanced in the second part of the _Riddle_ (chapters vi., x., and xi.). Ostwald has, however, caused some misunderstanding by insisting on substituting his idea of energy for the pure notion of substance (as Spinoza had formulated it), and by rejecting the other attribute of substance, matter. His supposed "Refutation of Materialism" is a mere attack on windmills; his energism (the consistent dynamism of Leibnitz, etc.) is just as one-sided as its apparent opposite, the consistent materialism of Democritus, Holbach, etc. The latter makes matter precede force; the former regards matter as the product of force. Monism escapes the one-sidedness of both systems, and, as hylozoism, refuses to separate the two attributes of substance, space-filling matter and active energy. This applies to mental life just as to any other natural process; our mental forces or phronetic energies are just as much bound up with the neuroplasm, the living plasm of the neurona in the cortex, as the mechanical energy of our muscles is with the contractile myoplasm, the living muscular substance.

In the exhaustive study of consciousness which I gave in the tenth chapter of the _Riddle_ I sought to show that this enigmatic function--the central mystery of psychology--is not a transcendental problem, but a natural phenomenon, subject to the law of substance, as much as any other psychic power. The child's consciousness only develops long after its first year, and grows as gradually as any other psychic function; like these, it is bound up with the normal anatomic and chemical condition of its organs, the phroneta in the cortex. Consciousness develops originally out of unconscious functions (as an "inner view," or mirroring, of the action of the phronema); and at any time an unconscious process in the cortex may come within the sphere of consciousness by having the attention directed to it. On the other hand, conscious actions, which need a good deal of attention when they are first learned (such as playing the piano), may become unconscious through frequent repetition and practice. The fact that chemical energy is converted in the phronetal cells during any of these actions is proved by the fatigue and exhaustion which prolonged mental work causes in the brain, just as mechanical work does in the muscles. Fresh matter has to be supplied by the food before the mental work can be continued. Moreover, it is well known that various drinks have a considerable influence on consciousness (coffee and tea, beer and wine); and the temporary extinction of it under chloroform or ether is an analogous fact. Again, the familiar phenomena of the dream, the deviations from normal consciousness, hallucinations, delusions, etc., must convince every impartial thinker that these mental functions are not of a metaphysical character, but physical processes in the neuroplasm of the brain, and thoroughly dependent on the law of substance.

In complete contrast to this natural monistic conception of the human mind, which is, in my opinion, definitely established by nineteenth-century science, we have the older dualistic estimate of it which is still widely accepted both by unlearned and learned, especially metaphysicians and theologians. I have already dealt in the _Riddle_ (chapter xi.) with the grounds for this belief in an immaterial soul, and expressed my conviction that "the belief in the immortality of the human soul is in flagrant contradiction to the soundest empirical principles of modern science." I must refer the reader to what I said there about thanatism and athanatism, only reminding him once more of the immense influence of the Kantist philosophy in maintaining this belief in the spirituality of the soul. Kant derived from the introspective study of his own gifted mind an extremely high estimate of human reason, and he fallaciously transferred this estimate to the human mind generally. He did not perceive that it is either wholly wanting in the savage, or does not rise much above the stage which has been reached by the intelligence of the dog, horse, elephant, and other advanced animals.

Modern anthropogeny has raised the theory of evolution to the rank of an historical fact. All the various organs of our body resemble those of our nearest relatives, the anthropoid apes, in their structure and composition. They only differ from them in details of form and size, which are determined by inherited variations of growth. But the functions as well as the organs have been inherited by man from his primate ancestors. This applies to the mind also, which is merely the collective function of the phronema, the central organ of thought. An impartial comparison of mental life in the anthropoid ape and the savage shows that the differences between the two are not more considerable than the differences in the structure of their brains. Hence, if one accepts the dualistic theory of the soul formulated by Plato and Kant and accepted by so many modern psychologists, it is necessary to attribute an immortal soul to the anthropoid apes and the higher mammals (especially to domestic dogs) just as well as to savage or civilized man (_cf._ chapter xi. of the _Riddle_).

The thorough and careful study of the mental life of the savage, supported by the results of anthropogeny and ethnography, has in the course of the last forty years decided the issue of this struggle between the conflicting theories of the origin of civilization. The older theory of degeneration, based on religious beliefs, and so preferred by theologians and theosophists, declared that man--the "image of God"--was created originally with perfect bodily and mental powers, and only fell away from his high estate after the original sin. On this view the present savages are degenerate descendants of the first godlike men. (In tropical lands the anthropoid apes are in similar fashion regarded by the natives as degenerate branches of their own stem!) Although this Biblical degeneration theory is still taught in most of our schools, and even supported by a few mystic philosophers, it had lost all scientific countenance before the end of the nineteenth century. It is now replaced by the modern theory of evolution, which was represented by Lamarck, Goethe, and Herder a century ago, and raised to a predominant position in ethnography by Darwin and Lubbock. It has taught us that human civilization is the outcome of a long and gradual process of evolution, covering thousands of years. The civilized races of our time have arisen from less civilized races, and these in turn from lower, until we reach the savage races which show no trace of civilization.

Ethnologists distinguish as a separate class the races which are found midway between the civilized peoples and the savages. We shall deal with their classification and characteristics later on (chapter xvii.). These races show some advance on the artistic instinct which we find in a slight degree even among the savages at times; moreover, their animal curiosity develops into human curiosity, and raises the question of the causes of phenomena, the germ of all science.

Civilized races, which occupy the next stage to these, are raised above them by the formation of larger states and a greater division of labor. The specialization of the various groups of workers and the greater ease of maintenance permit a further development of art and science. To these groups belong, of living races, the majority of the Mongolians, and the greater part of the inhabitants of Europe and Asia in ancient and mediæval times. The great ancient civilizations of China, Southern India, Asia Minor, Egypt, and afterwards of Greece and Italy, show not only a great development of art and science, but also a concern for legislation, religious worship, education of the young, and the spread of knowledge by written books.

Civilization in the narrower sense, characterized by a high development of art and science and the manifold application of them to practical life in legislation, education, etc., was greatly advanced even in antiquity among several nations--in Asia by the Chinese, Southern Indians, Babylonians, and Egyptians; in Europe by the Greeks and Romans of the classic age. However, their results were at first restricted to narrow fields, and were mostly lost during the Middle Ages. Modern civilization rose to importance about the end of the fifteenth century, when the invention of printing had made possible the spread of knowledge far and wide, the discovery of America and circumnavigation of the globe had widened the horizon, and the Copernican system had demolished the error of geocentricism. Then began the many-sided growth of civilization which has reached so marvellous a height in the nineteenth century through the extraordinary development of science. Then at last free reason could triumph over the prevailing mediæval superstition.

XV

THE ORIGIN OF LIFE

The miracle of the origin of life--Creation of species: Moses and Agassiz--Creation of the first cells: Wigand and Reinke--Agnostic position: resignation--Eternity hypothesis (dualistic, Helmholtz; monistic, Preyer)--Archigony hypothesis (autogony hypothesis, Haeckel, Nägeli; cyanic hypothesis, Pflüger, Verworn)--Spontaneous generation--Saprobiosis or necrobiosis--Experiments in spontaneous generation--Pasteur--Stages of archigony--Observation of archigony--Synthesis of plasma--Value of the unsuccessful experiments to produce plasm artificially--The logic of modern experimental biology.

The question of the origin of life is one of the most important and interesting, but one of the most difficult and complicated, problems with which the mind of man has been occupied for thousands of years. There are few other questions (such as the freedom of the will or personal immortality) on which such different and contradictory views have been expressed, and few that remain so far from being closed at the present day. There are, moreover, few problems on which the opinions of even distinguished thinkers diverge so much, and have degenerated so much into fantastic hypotheses. This is partly due to the extreme difficulty of giving a strictly scientific solution of the problem and partly to the confusion of ideas which is so great in this controversy, the lack of clear rational insight, and the powerful authority of the prevailing religious faith and other venerable dogmas.

The easiest and quickest thing to do is to cut the Gordian knot of the question with the sword of faith, or answer it with a belief in a supernatural creation. The first article of the creed was given to us in childhood as the foundation of all cosmic philosophy. It is based on the Mosaic account of creation in the first chapter of Genesis. As I have fully examined its scientific value in the second chapter of my _History of Creation_, I may refer the reader thereto. It is unquestionable that this myth still has a very great practical influence; the great majority of the clergy cling to it because it is found in the infallible "word of God." Most governments, which hold blind faith to be an important element of education, include it in the code for the elementary school. On the other hand, it is difficult to find a man of science who will uphold it to-day. The gifted Louis Agassiz made one of the most remarkable attempts to do this in his _Essay on Classification_ (1858), a book that appeared almost contemporaneously with Darwin's epoch-making _Origin of Species_, and dealt with the general problems of biology from the directly opposite, the mystic, point of view. According to Agassiz, each species of animal or plant is an "incarnate thought of the Creator."

Differing from this Biblical fancy of the supernatural creation of each species, two botanists, Wigand of Marburg and Reinke of Kiel, have lately restricted the action of the celestial architect very considerably; they have ascribed to him only the creation of the primitive cells, which he is supposed to have endowed with the power to develop into the higher organisms. Wigand assumed for the origin of each species a special primitive cell and a long phylogenetic development of this; Reinke prefers a stem, composed of a number of species. These modern creative theories have no more scientific value than that of Agassiz; they are equally based on pure superstition (_cf._ chapters i.-iii.).

A different attitude from this irrational positive superstition is the sceptical view of those scientists who regard the question of the origin of life as insoluble or transcendental. Darwin and Virchow are representatives of this agnostic position; they held that we know nothing, and can know nothing, about the origin of the first organisms. Darwin, for instance, explains in his chief work that he "has nothing to do with the origin of the fundamental spiritual forces, or with that of life itself." This is a complete abandonment of the task of solving a scientific problem which must present as definite a subject of inquiry to modern research as any other evolutionary problem. The origin of life on our planet represents a fixed point in its history. However, there is nothing to be said if a scientist chooses to make no inquiry into it. A number of distinguished modern scientists maintain this agnostic attitude; they are more or less convinced that the origin of life is a natural process, but believe we have not as yet the means to explain it.

Different, again, is a third attitude which regards the problem of the origin of life as extremely difficult, yet capable of solution. This is the position of Dubois-Reymond, for instance, who counts the origin of life as the third great cosmic problem. Most of the modern scientists who have worked on the problem are of this opinion, although their views as to the way of solving it differ very much. We are confronted, in the first place, with two essentially different views which we may call the eternity-hypothesis and the theory of archigony (or spontaneous generation). According to the first view, organic life is eternal; according to the second, it began at a definite point of time. The eternity-hypothesis has assumed two very different forms, one of which has a dualistic and the other a monistic base. Helmholtz is a representative of the former theory, and Preyer of the latter.

Hermann Eberhard Richter put forward, in 1865, the hypothesis that infinite space is full throughout of the germs of living things, just as it is of inorganic bodies; both of them are in a condition of eternal development. When the ubiquitous germs reach a mature and habitable cosmic body, which possesses heat and moisture in the proper degrees for their development, they break into life, and may lead to the formation of a whole world of living things. Richter conceives these ubiquitous germs as living cells, and formulates the principle: _Omne vivum ab æternitate e cellula_ (Every living thing is eternal and from a cell). In much the same way the botanist Anton Kerner postulates the eternity of organic life and its complete independence of the inorganic world. But the difficulties encountered by this hypothesis, in the indefinite form that Kerner gives it, are so great and so obvious that his theory has won no recognition.

However, the "cosmozoic hypothesis" attained a great popularity when it was afterwards taken up by two of the most distinguished physicists, Hermann Helmholtz and Sir W. Thomson (Lord Kelvin). Helmholtz formulated the alternative thus (in 1884): "Organic life either came into existence at a certain period, or it is eternal." He declared for the latter view, on the ground that we have not succeeded in producing living organisms by artificial means. He supposes that the meteors that roam about the universe might contain the germs of organisms, and, under favorable conditions, these might reach the earth or other planets and develop thereon. This cosmozoic hypothesis of Helmholtz is untenable, because the physical features of space (the extreme temperatures, the absolute dryness, the absence of atmosphere, etc.) exclude the lasting existence of plasm on meteorites in the form of organic germs with a capacity to live. The hypothesis is, moreover, logically useless, since it does not solve, but postpones, the question of the origin of organic life. If it is consistently worked out, it leads to pure cosmological dualism.

Another and very different theory of the eternity of life has been elaborated by Theodor Fechner (1873) and Wilhelm Preyer (1880). Both these scientists extend the idea of life to the whole cosmos, and reject the distinction that is usually drawn between the organic and the inorganic. Fechner goes so far as to ascribe consciousness to the whole universe and every single body in it, and regards individual organisms merely as parts of one vast universal organism. His system is, therefore, panpsychistic, and, at the same time, pantheistic, as he somewhat mystically connects the idea of a conscious God with that of a living universe. Preyer generally agrees with him in extending the idea of life to the whole universe, and conceiving it as an organism. He applies his theory in the symbolic sense which I alluded to on page 38, and described as impracticable. The fiery mass of the forming earth is the gigantic organism, and Preyer gives the name of "life" to its rotatory movement (or gravitational energy). As it cooled down, the heavier metals (the dead inorganic masses) separated from it; from the rest of it were formed first simple and afterwards complex carbon-combinations, and finally albumin and plasm. This extension of the word "organism" has very properly met with little approval in biology. It only increases the confusion, and the difficulty of marking off biological from abiological science, which is both practically necessary and theoretically justified.

If, then, in our opinion, the eternity-hypotheses are of no more value than the creation-hypotheses, we have left, for the purpose of answering the great question of the origin of life, only the third group of scientific theories which I have combined under the general head or archigony. They start from the following points: 1. Organic life is everywhere bound up with the plasm (or protoplasm), a chemical substance of a viscous character, having albuminous matter and water as its chief constituents. 2. The characteristic movements of this living substance, to which we give the name of organic life, are physical and chemical processes, that can only take place within certain limits of temperature (between the freezing-point and boiling-point of water). 3. Beyond these limits organic life may in certain circumstances be maintained for a time in a latent condition (apparent death, potential life); but this latent condition is restricted to a certain (and generally short) period. 4. As the earth, like all the other planets, was for a long time in a state of incandescence, at a temperature of several thousand degrees, living organisms (viscous albuminoids) cannot possibly have existed on it, and so cannot be eternal. 5. Fluid water, the first condition for the appearance of organic life, cannot have formed on it until the crust at the surface had fallen below boiling-point. 6. The chemical processes which first set in at this stage of development must have been catalyses, which led to the formation of albuminous combinations, and eventually of plasm. 7. The earliest organisms to be thus formed can only have been plasmodomous monera, structureless organisms without organs; the first forms in which the living matter individualized were probably homogeneous globules of plasm, like certain of the actual chromacea (_chroococcus_). 8. The first cells were developed secondarily from these primitive monera, by separation of the central caryoplasm (nucleus) and peripheral cytoplasm (cell-body).

The monistic hypothesis of abiogenesis, or autogony (= self-development) in the strictly scientific sense of the word, was first formulated by me in 1866 in the second book of the _General Morphology_. The solid foundation for it was found in the monera I had described, the very simple organisms without organs that had up to that time been overlooked or thrust aside. It is of radical importance, in giving a naturalistic solution of the problem of the origin of life, to start from these structureless granules of living matter, and not--as still generally happens--from the cell; these nucleated elementary organisms could not be the earliest archigonous living things, but must have been evolved secondarily from the unnucleated monera. Hence, I made a very thorough study of these rudimentary organisms in my _Monograph on the Monera_ (1870), and endeavored to formulate it more clearly later on (in the first volume of the _Systematic Phylogeny_). In regard to the chemical question of the first formation of plasm and its inorganic preparation, Edward Pflüger conducted some valuable investigations, and recognized that the radical of cyanogen was the chief element of the living plasm. I may therefore distinguish two different stages of the theory--my own older autogony-hypothesis and the later cyanogen-hypothesis.

The theory of abiogenesis, or archigony, which I advanced in 1866, and have developed in later writings, appeals directly to the biochemical facts that modern vegetal physiology has firmly established. The chief of these facts is that even the living green plant-cell has the synthetic faculty of plasmodomism or carbon-assimilation; that is to say, it is able to build up, by a chemical synthesis and reduction, from simple inorganic compounds (water, carbonic acid, nitric acid, and ammonia), the complex albuminous compounds which we call plasm or protoplasm, and which we regard as the active living substance and the true material basis of all vital function (_cf._ chapter vi.). All botanists are now agreed that this most important process of vegetal life, the fundamental process of all organic life and all organization, is a purely chemical (or, in the wider sense, physical) process, and that there is no question of a specific vital force or a mystic constructor (like the famous "mechanical engineer of life"), or any other transcendental agency, in connection with it. The tiny chemical laboratory in which this remarkable organoplastic process takes place under the influence of sunlight is, in the simplest plants, the chromacea, either the whole homogeneous globule of plasm (_chroococcus_) or its bluish-green surface-layer, which is active as a chromatic principle (chromatophore). But in most plants these reduction-laboratories are the chromatella or chromatophora, which have been differentiated from the rest of the plasm of the cell, and are colorless globular leucoplasts within its dark interior, or green chromoplasts (or granules of chlorophyll) at its illumined surface. My theory of archigony only assumes that this chemical process of plasmodomism which we find repeated every second in every plant-cell exposed to the sunlight, and which has become an "inherited habit" of the green plant-cell, developed of itself at the beginning of organic life; in other words, it is a catalytic process (or one analogous to catalysis), the physical and chemical conditions of which were present in the condition of organic nature at that time.

My hypothesis was very strongly confirmed twenty years ago by the adhesion of the able botanist, Carl Nägeli. In his instructive work, _A Mechanical-physiological Theory of Evolution_ (1884), he supported all the principal ideas as to the natural origin of life which I had advanced in 1866. He formulates the chief part of them in this admirable principle:

The origin of the organic from the inorganic is, in the first place, not a question of experience and experiment, but a fact deduced from the law of the constancy of matter and force. If all things in the material world are causally related, if all phenomena proceed on natural principles, organisms, which are formed of and decay into the same matter, must have been derived originally from inorganic compounds.

This excellent and clear declaration of a distinguished scientist and profound thinker might be taken to heart by the "exact" scientists who are always attacking the monistic theory of archigony as an unproved hypothesis, or regard the whole problem as insoluble. Nägeli has, moreover, proceeded to make a thorough study of the molecular processes involved, and embodied the results in his idioplasm theory. He believes that at the beginning of organization the definite autonomous arrangement of the smallest homogeneous parts of the plasm was a matter of the greatest importance. In his opinion these "micella" are crystalline groups of molecules, arranged multifariously in strings and parallel rows.

A similar and more elaborate attempt to give a physical explanation of the processes of archigony and trace them to mechanical molecular structures was made by Ludwig Zehnder in 1899 in his work on _The Origin of Life_. He believes that the smallest and lowest life-unities (the micellar strings of Nägeli and the biophora of Weismann, corresponding to my plastidules) have a tubular shape, and so he calls them "fistella." He supposes that these invisible molecular structures are regularly arranged in millions in the plasma of the cell, and differentiated in such a way that some will effect endosmosis, others contraction, others the conduction of stimuli, and so on. As in the similar work of Nägeli and others, the value of this molecular hypothesis is that it stimulates us to attempt to conceive the mode of the arrangement and movement of the molecules of plasm in the process of archigony on physical principles.

A more interesting and notable attempt to penetrate into the mysterious obscurity of the chemical processes in archigony was made in 1875 by the distinguished physiologist, Edward Pflüger, in his essay on _Physiological Combustion in the Living Organism_. He starts from the fact that the plasm (or protoplasm) is the material basis of all vital phenomena, and that this living matter owes its properties to the chemical properties of the albumin (whether we regard this as a chemical unity, protein or protalbumin, or as a mixture of different compounds). However, Pflüger sharply distinguishes between the living albumin of the plasm out of which all organisms are built, and the dead albumin, such as we find it, for instance, in the glairy albumin of the hen's egg. Only the living albumin (plasm) decomposes of itself in a slight degree, and to a greater extent under the influence of external excitation; the dead albumin will remain intact for a long time under favorable conditions. The cause of the extraordinary instability of the living albumin is its intramolecular oxygen--that is to say, the oxygen that is taken into the interior of the plasma-molecules in breathing, and effects there a disassociation, surrounding the atoms and breaking up the new-formed groups.

The real cause of this rapid decomposability of the plasm, and of the accompanying formation of carbonic acid, is found in the cyanogen, a remarkable body composed of an atom of carbon and an atom of nitrogen, which, in conjunction with potassium, forms the well-known and very virulent poison, cyanide of potassium. The non-nitrogenous decomposition-products of the dead and the living albumin agree in the main, but their nitrogenous products are totally different. Uric acid, creotin, guanine, and the other decomposition products of plasm contain the cyanogen-radical, and the most important of all, urea, can be artificially produced from cyanic compounds, as Wöhler showed in 1828. From this we may infer that the living albumin always contains the cyanogen-radical, and that dead nutritive albumin does not. The belief that it is cyanogen which gives its characteristic vital properties to the plasm is supported by a number of analogies that we find to exist between cyanide compounds, especially cyanic acid (C N O H.) and the living albumin. Both bodies are fluid and transparent at a low temperature, while they set at a higher; both of them break up in the presence of water into carbonic acid and ammonia; both produce urea by disassociation (by the intramolecular surrounding of the atoms, not by direct oxydation). "The similarity of the two substances is so great," says Pflüger, "that I might describe cyanic acid as a semi-living molecule." Both substances grow in the same way by concatenation of the atoms, homogeneous groups of atoms joining together chainwise in large masses.

There is an especial interest in connection with the theory of archigony and its physical basis in the chemical fact that cyanogen and its compounds--cyanide of potassium, cyanic acid, cyanide of hydrogen, etc.--are only formed at incandescent heat; that is to say, when the requisite inorganic nitrogenous compounds are put with glowing coals, or the mixture is heated to incandescence. Other essential constituents of albumin, such as carburetted hydrogen or alcohol-radical, can be formed synthetically in heat. "Thus," says Pflüger, "nothing is clearer than the possibility of the formation of cyanic compounds when the earth was entirely or partially in a state of incandescence or great heat. We see how extraordinarily all the facts of chemistry point to fire as the force that has produced the constituents of albumin by synthesis. Hence life was born from fire, and the chief conditions of its appearance are associated with a time when the earth was a glowing ball of fire. When we remember the incalculably long period in which the surface of the earth was slowly cooling, we see that cyanogen, and the compounds that contained cyanogen, and carburetted hydrogen, had plenty of time and opportunity to follow out to any extent their great tendency to the transposition and formation of polymeria (chains of atoms), and, with the co-operation of oxygen and afterwards of water and salts, to evolve into the self-decomposable albumin which is living matter." In regard to the latter feature, it is well to emphasize the fact that, as will be understood, there must have been a long series of chemical intermediary stages between the incandescent formation of cyanogen and the appearance of the aqueous living plasm.

Pflüger's cyanogen theory does not conflict with my monera theory, but rather supplements it, by its careful and thoroughly scientific study of a much earlier stage of primitive biogenesis--in a sense, the first period of preparation for the formation of albumin. This must be well borne in mind in view of the attacks which have lately been made on it by Neumeister and other vitalists; it is supposed to be untenable, because "there is an impassable gulf between cyanic compounds and proteids." This criticism is answered by the living albumin itself, which always contains in its nitrogenous decomposition products the radical of cyanide or other substances (urea) that can be artificially produced from cyanic compounds. Another objection is that "the cyanic compounds which were formed in the heat must have very quickly perished on the subsequent appearance of water." The objection has no weight, since we can form no definite idea as to the special conditions of chemical activity in those times. We can only say that the conditions during this long period (embracing millions of years) were totally different from those of chemical action at the surface of the earth to-day. The real ground of the opposition of Neumeister and other vitalists is their dualistic conception of nature, which will maintain at all costs the deep gulf between the organic and inorganic worlds.

Max Verworn, in his _General Physiology_, has fully described and criticised the various theories of the appearance of life on the earth. He rightly attributes a great value to Pflüger's cyanogen theory, because "it makes a strictly scientific study of the problem in close relation to the facts of physiological chemistry, and goes thoroughly into detail." He agrees with Pflüger when he expresses himself as follows: "I would say, therefore, that the first albumin to be formed was in point of fact living matter, endued with the property in all its radicals of attracting especially homogeneous parts with great force and preference, in order to build them chemically into the molecule, and so grow indefinitely. On this view the living albumin need not have a constant molecular weight, because it is a huge molecule in an unceasing process of formation and decomposition, probably acting on the ordinary chemical molecules as a sun does on a small meteor." This theory, which I believe to be correct, is also maintained by many other modern scientists who have made a particular study of the difficult question of the nature and origin of the albuminoids.

Now that we have described the various modern theories of archigony that are worth considering, and recognized with Nägeli that the original development of the organic from the inorganic is a fact, we may glance at the older theories which, under the name of "spontaneous generation," afforded matter for a good deal of controversy. It is true that they are now almost entirely abandoned, but the experiments in connection with them excited a good deal of interest and led to many misunderstandings.

The older hypotheses of "spontaneous generation" do not bear on our problem of archigony (or the first development of living matter from lifeless inorganic carbon compounds) but relate to the formation of lower organisms out of the putrid and decomposing organic elements of higher organisms. In order to distinguish these hypotheses from the totally different theory of archigony, it is better to give them the name of saprobiosis (an earlier name was necrobiosis), which means the birth of living from dead (_nekron_) or putrid (_sapron_) organic matter. Saprobiosis is preferable, because necrobiosis is better used in a different sense, for the dead organic parts which gradually bring about the death of the living body (see p. 106). It was believed in ancient times that lower organisms could arise from the dead remains of higher organisms, such as fleas from manure, lice from morbid pustules in the skin, moths from old furs, and mussels from slime in the water. As these stories were supported by the authority of Aristotle, and on that account believed by St. Augustine and other fathers, and reconciled with the faith, they were held until the beginning of the eighteenth century. Even in the year 1713 the botanist Heucherus stated that the green duck-weed (_lemna_) is only condensed grease from the surface of foul standing water, and that water-cress was formed from it in fresh running water.

The first scientific refutation of these old stories was made by the Italian physician, Francisco Redi, in 1674, on the basis of very careful experiment: he was persecuted for "unbelief" on that account. He showed that all these animals arose from eggs that had been deposited by female animals in dung, skin, fur, slime, etc. But at that time the proof could not be extended to the tape-worms, maw-worms, and other intestinal animals (_entozoa_), which live inside other animals (in the bowels, blood, brain, or liver). It was still believed that these arise from diseased parts of the host-animals in which they live, until about the middle of the nineteenth century. It was not until 1840-1860 that it was shown by the experiments of Siebold, Leuckart, Van Beneden, Virchow, and other famous biologists, that all these intestinal animals have come from without into the animals they live in, and propagate there by eggs. Of late years the proof has been applied all round.

On the other hand, the hypothesis of saprobiosis retained its position until quite recently for one section of the smallest and lowest organisms, the microscopic forms of life, invisible to the naked eye, which were formerly called infusoria, and which we now call by the wider name of protists or unicellulars. When Leeuwenhoek discovered the infusoria in 1675 with the newly invented microscope, and showed that they arise in great quantities in infusions of hay, moss, flesh, and other putrid organic substances, it was generally believed that they were spontaneously generated there. The Abbé Spallanzani showed in 1687 that no infusoria appear in these infusions if they are well boiled and the vessel is carefully closed; the boiling kills the germs in them, and the exclusion of air prevents the entrance of fresh germs. In spite of this, many microscopists still believed that certain infusoria, particularly the very small and simple bacteria, could be born directly from putrid or diseased tissues of organisms, or from decomposing organic fluids; the opinion was maintained by Pouchet at Paris in 1858, and afterwards by Charlton Bastian. The controversy about the subject moved the Paris Academy in 1858 to offer a prize for "careful research that would throw new light on the question of spontaneous generation." It fell to the famous Louis Pasteur, who proved, by a series of ingenious experiments, that there are everywhere in the atmosphere numbers of germs of microbes or microscopic organisms floating among the dust particles, and that these grow and reproduce when they reach water. Not only infusoria, but also small highly organized plants and animals--such as lichens, mosses, rotifers, and tardigrades--can live for months in a desiccated condition, be carried in all directions by the wind, and reawaken into life when they reach water. On the other hand, Pasteur showed convincingly that organisms never appear in infusions of organic substances when they are sufficiently boiled and the atmosphere that reaches them has been chemically purified. He summed up the results of his rigorous experiments, which were confirmed by Robert Koch and other bacteriologists, and gave rise to the modern precautions as to disinfection, in the maxim: "Spontaneous or equivocal generation is a myth."

The famous experiments of Pasteur and his successors had destroyed the myth of saprobiosis, but not the theory of archigony. These entirely different hypotheses are still very frequently confused, because the old title of "spontaneous generation" is used for both. We still read sometimes that the "unscientific" belief in abiogenesis has been definitely refuted by these experiments, and that the question of the origin of life has thus become an insoluble enigma. There is an astonishing superficiality and lack of discernment in such remarks; they would hardly be possible in any other branch of science. But in biology--many of its distinguished representatives continue to say--we have only to observe and correctly describe facts; the formation of clear ideas and the indulgence in reflection on the facts are unnecessary and dangerous, and, therefore, to be avoided! It is due to this pitiable condition of biological methods of research that our hypothesis of archigony is still attacked, or else ignored. Why? Because the false hypothesis of saprobiosis, which has absolutely nothing in common with it but the name "spontaneous generation," has been refuted by the experiments of Pasteur and his colleagues![9] These experiments prove nothing whatever beyond the fact that new organisms are not formed in certain infusions of organic matter--under definite, artificial conditions. They do not even touch the important and pressing question, which alone interests us: "How did the earliest organic inhabitants of our earth, the primitive organisms, arise from inorganic compounds?"

The great popularity of the famous experiments of Pasteur on spontaneous generation, and the unfortunate confusion of ideas which was caused by the false interpretation of his results, make it necessary for me to say a word on the general value of scientific experiments in many questions. Since Bacon introduced experiment into science three hundred years ago, and gave it a logical basis, both our speculative knowledge of nature and the practical application of our knowledge made remarkable progress. New methods of research made it possible for modern workers to penetrate far more deeply into the nature of phenomena than the older thinkers had done, who had no knowledge of experiment. Especially in the nineteenth century the development of the experimental method, or the putting of a question to nature, led to enormous advances in the various sciences.

In the subject we are considering the question to be put to nature is: "Under what conditions and in what manner is living matter (or plasm) formed from lifeless inorganic compounds?" We may confidently assume that in the period when archigony took place--the time when organic life first appeared on the cooled surface of the earth, at the beginning of the Laurentian Age--the conditions of existence were totally different from what they are now; but we are very far from having a clear idea of what they were, or from being able to reproduce them artificially. We are just as far from having a thorough chemical acquaintance with the albuminous compounds to which plasm belongs. We can only assume that the plasma-molecule is extremely large, and made up of more than a thousand atoms, and that the arrangement and connection of the atoms in the molecule are very complicated and unstable. But of the real features of this intricate structure we have as yet no conception. As long as we are ignorant of this complex molecular structure of albumin, it is useless to attempt to produce it artificially. Yet in this position of the matter we would seek to produce that great wonder of life, the plasm, artificially, and when the experiment miscarries (as we should expect) we cry out: "Spontaneous generation is impossible."

When we carefully consider the intelligent experiments that have been made in regard to archigony in the light of these facts, it is clear that their negative result does not in the slightest degree affect our question. The much-admired experiments of Pasteur and his colleagues prove merely that in certain artificial conditions infusoria are not formed in decomposing organic compounds (or the dead tissues of highly organized histona); they cannot possibly prove that saprobioses of this kind do not take place under other conditions. They tell us nothing whatever about the possibility or reality of archigony; in the form in which I put the scientific hypothesis in 1866 it is completely untouched by all these experiments. It remains intact as the first attempt to give a provisional reply--if only in the form of a temporary hypothesis--on the basis of modern science to one of the chief questions of natural philosophy.

In my _General Morphology_ (1866), and afterwards in my _Biological Studies on the Monera and other Protists_, and the first volume of my _Systematic Phylogeny_ (1894), I attempted to sketch in detail the stages of the process to which I give the name of archigony. I distinguished two principal stages--_autogony_ (the formation of the first living matter from inorganic nitrogenous carbon-compounds) and _plasmogony_ (the formation of the first individualized plasm; the earliest organic individuals in the form of monera). In more recent efforts I have made use of the important results reached by Nägeli (1884) in his investigations of the same subject. In regard to some important points relating to the chemico-physical part of the question, Nägeli has, in his _Mechanico-physiological Theory of Evolution_ (chapter ii.), gone more into the details of the process of archigony. To the earliest living things, which were formed by "unicellular organization" of the plasm out of simple inorganic compounds, he gives the name of _probia_ or _probionta_, and thinks that these had an even simpler structure than my monera. This view seems to rest on a misunderstanding. Nägeli does not strictly follow my definition, "organisms without organs" (that is to say, structureless living particles of plasm without morphological differentiation), but he has in mind the individual rhizopod-like organisms which I had at first described as monera--_protamœba_, _protogenes_, _protomyxa_, etc. In my present view the chromacea, or plasmodomous phytomonera, are much more important than these plasmophagous zoomonera. It is curious that Nägeli does not make thorough use of their primitive organization for the establishment of his theory, although he has had the great merit of describing these most primitive of all living organisms as unicellular algæ (1842). As a matter of fact, the simplest chromacea (chroococcus and related forms) approach so closely to his hypothetical probia or probionta that the only things we can regard as the rudiments of organization in the chroococcacea are the secretion of a protective membrane about the homogeneous plasma-globule and the separation of the blueish-green cortical zone from the colorless central granule. The more important of the further conclusions of Nägeli are those which relate to the mode of the primitive abiogenesis and the frequent repetition of this physical process.

Recently Max Kassowitz, in the second volume of his _General Biology_ (1899), has gone fully into the various stages of the process of archigony, as a sequel to his metabolic theory of the building up and decay of plasm, from the point of view of physiological chemistry. He says very truly that the development of living from lifeless matter must not be conceived as a sudden leap; the very complicated chemical unities which now form the basis of life have been slowly and gradually evolved during an incalculably long period by the way of substitution for simpler compounds. We may join these views--which generally accord with my earlier deductions--with Pflüger's cyanogen theory, and so draw up the following theses:

1. A preliminary stage to archigony is the formation of certain nitrogenous carbon-compounds which may be classed in the cyanic group (cyanic acid, etc.). 2. When the crust of the earth stiffened, water was formed in the fluid condition; under its influence, and in consequence of the great changes in the carbonic-acid laden atmosphere, a series of complicated nitrogenous carbon-compounds were formed from these simple cyanic compounds, and these first produced albumin (or protein). 3. The molecules of albumin arranged themselves in a certain way, according to their unstable chemical attractions, in larger groups of molecules (pleona or micella). 4. The albumin-micella combined to form larger aggregations, and produced homogeneous plasma-granules (plassonella). 5. As they grew the plassonella divided, and formed larger plasma-granules of a homogeneous character: monera (= probionta). 6. In consequence of surface-strain or of chemical differentiation, there took place a separation of the firmer cortical layer (membrane) from the softer marrow layer (central granule), as in many of the chromacea. 7. Afterwards the simplest (nucleated) cells were formed from these unnucleated cytodes, the hereditary mass of the plasm gathering within the monera and condensing into a firm nucleus.

It is an interesting, but at present unanswered, question whether the process of archigony only occurred once in the course of time or was frequently repeated. Reasons can be given for both views. Pflüger says: "In the plant the living albumin only continues to do what it has done ever since its origin--constantly to regenerate itself or to grow; hence I believe that all the albumin in the world comes from that source. On that account I doubt if spontaneous generation takes place in our time. Moreover, comparative biology directly shows that all life has come from one single root." However, this view does not exclude the possibility of the chemical process of spontaneous plasmodomism having been frequently repeated--under like conditions--in the same form in primordial times.

On the other side, Nägeli especially has pointed out that there is no reason to prevent us from thinking that archigony was repeated several times, even down to our own day. Whenever the physical conditions for the chemical process of plasmodomism were given, it might be repeated anywhere at any time. As to locality, the sea-shore probably affords the most favorable conditions; as, for instance, on the surface of fine moist sand the molecular forces of matter in all its conditions--gaseous, fluid, viscous, and solid--find the best conditions for acting on each other. It is a fact that to-day all the various evolutionary forms of living matter--from the simplest moneron (chroococcus) to the plain nucleated cell, from this to the highly organized cell of the radiolaria and infusoria, from the simple ovum to the most elaborate tissue-structure in the higher plants and animals, from the amphioxus to man--come in an order of succession. There are only two ways of explaining this fact: either the simplest living organisms, the chromacea and bacteria, the palmella and amœbæ, have remained unchanged or made very little advance in organization since the beginning of life--more than a hundred million years; or else the phylogenetic process of their transformation has been frequently repeated in the course of this period, and is being repeated to-day. Even if the latter were the case, we should hardly be in a position to learn it by direct observation.

Assuming that the simplest organisms are still formed by abiogenesis, the direct observation of the process would probably be impossible, or at least extremely difficult, for the following reasons: 1. The earliest and simplest organisms are most probably globular particles of plasm, without any visible structure, like the simplest living chromacea (_chroococcus_). 2. These plasmodomous monera cannot be distinguished from the chromoplasts (chlorophyll-granules), which live inside plant-cells, and may continue after the death of the cells to multiply independently by cleavage. 3. We must admit with Nägeli that the original size of these probionta (in spite of the relatively colossal size of their molecules) is very small--much too small to come within the range of the best microscope. 4. In the same way the primitive metabolism and the slow, simple growth of these monera would not come within direct observation. 5. As a matter of fact, we do often find in stagnant water, and in the sea, tiny granules which consist, or seem to consist, of plasm. We usually regard them as detached portions of dead animals or plants; little isolated chlorophyll-granules that may be found everywhere are looked upon as rejected products of vegetal cells. But who could refute the assumption that they are really plassonella or young monera, which grow slowly and unite with similar particles to form larger plasmic bodies?

It is often objected to our naturalistic and monistic conception of archigony that we have not yet succeeded in forming albuminous bodies, and especially plasm, in our chemical laboratories by artificial synthesis; from this the perverse dualistic conclusion is drawn that it is only supernatural vital forces that can do this. It is forgotten that we do not yet know the complicated structure of albuminous bodies, and that we do not yet know what really happens inside the green chlorophyll-granules which in every plant-cell convert the radiant energy of sunlight into the virtual energy of the new-formed plasm. How can we be expected to reproduce synthetically, with the imperfect and crude methods of present chemistry, an elaborate chemical process the nature of which is not analytically known to us? However, the worthlessness of this sceptical objection is obvious: we can never claim that a natural process is supernatural because we cannot artificially reproduce it.

XVI

THE EVOLUTION OF LIFE

Inorganic and organic evolution--Biogenesis and cosmogenesis--Mechanical evolution--Mechanics of phylogenesis--Theory of selection--Theory of idioplasm--Phyletic vital force--Theory of germ-plasm--Progressive heredity--Comparative morphology--Germ-plasm and hereditary matter--Theory of mutation--Zoological and botanical transformism--Neo-Lamarckism and Neo-Darwinism--Mechanics of ontogenesis--Biogenetic law--Tectogenetic ontogeny--Experimental evolution--Monism and biogeny.

I fully explained in my _General Morphology_ (1866) the profound importance of the science of evolution in relation to our monistic philosophy. A popular synopsis of this is given in my _History of Creation_, and is briefly repeated in the thirteenth chapter of the _Riddle_. I must refer the reader to these works, especially the latter, and confine myself here to a consideration of some of the principal general questions of evolution in the light of modern science. The first thing to do is to compare the conflicting views on the nature and significance of biogenesis which still face each other at the beginning of the twentieth century.

The essential unity of inorganic and organic nature, which I endeavored to establish in the second book of the _General Morphology_, and the significance of which I explained in the fourteenth chapter of the _Riddle_, is found through the whole course of its development, in the causes of phenomena and their laws. Hence, in dealing with the evolution of organisms, we reject vitalism and dualism, and maintain our conviction that it can always be traced to physical forces (and especially chemical energy). As we regard plasm as the basis of it (chapter vi.), we may say that organic evolution depends on the mechanics and chemistry of the plasm. We postulate no supernatural vital force for the explanation of physiological functions, and we are just as far from admitting it as regulator or agency of the biogenetic process.

If we understand by biogeny the sum total of the organic evolutionary processes on our planet, by geogeny the processes at work in the formation of the earth itself, and by cosmogony those that produced the whole world, biogeny is clearly only a small part of geogeny, and this in turn only a small section of the vast science of cosmogony. This important relation is evident enough, yet often overlooked; it holds both of time and space. Even if we suppose that the biogenetic process occupied more than a hundred million years, this period is probably much shorter than that which our planet has needed for its development as a cosmic body--from the first detachment of the nebular ring from the shrinking body of the sun to its condensation into a rotating sphere of gas, and from this to the formation of the incandescent globe, the stiffening of the crust at its surface, and finally the downpour of fluid water. It was not until this last stage that carbon could begin its organogenetic activity and proceed to the formation of plasm. But even this long geogenetic process is, as regards space and time, only a very small part of the illimitable history of the world. If we further assume that organic life develops on other cosmic bodies (_Riddle_, chapter xx.) in the same way as on our earth under like conditions, the whole sum of all these biogenetic processes is only a small part of the all-embracing cosmogenetic process. The vitalistic belief that its mechanical course was interrupted from time to time by the supernatural creation of organisms is opposed to pure reason, the unity of nature, and the law of substance. We must, therefore, hold fast above all to the conviction that all biogenetic processes are just as reducible to the mechanics of substance as all other natural phenomena.

The mechanical and natural character of the development of inorganic nature, the earth and the whole material world, was established mathematically at the end of the eighteenth century by the great atheist Laplace in his _Mécanique Céleste_ (1799). The similar cosmogony which Kant had expounded in 1755 in his _General Natural History and Theory of the Heavens_ only obtained recognition at a later date (_Riddle_, chapter xiii.). But the possibility of giving a mechanical explanation of organic nature was not seen until Darwin provided a solid foundation for the theory of descent by his theory of selection in 1859. I made the first comprehensive attempt to do this in 1866 in my _General Morphology_, the aim of which is expressed in the title: "General outlines of the science of organic forms, mechanically grounded on Darwin's improvement of the theory of descent." Especially in the second volume of the work, the "General Evolution of Organisms," I endeavored to show that both sections of the science, ontogeny (or embryology) and phylogeny, can be reduced to physiological activities of the plasm, and so explained mechanically, in the wider meaning of the word.

When I stated the nature and the aim of phylogeny in 1866, most biologists regarded my attempt as unjustifiable, as they did Darwinism itself, of which it was a natural consequence. Even the famous Émil Dubois-Reymond, to whom as a physiologist it should have been welcome, described it as "a poor romance"; he compared my first attempts to construct the genealogical tree of the organic classes, on the evidence of paleontology, comparative anatomy, and ontogeny, to the hypothetical labors of philologists to draw up the genealogical tree of the legendary Homeric heroes. As a matter of fact, I had myself described my imperfect effort as merely a provisional sketch, as a temporary hypothesis that would open the way for later and better research. A single glance at the immense literature of phylogeny to-day shows how much has been done since in this province, and how far we have advanced in the establishment of the features of evolution by means of the united labors of numbers of able paleontologists, anatomists, and embryologists. Ten years ago I attempted, in the three volumes of my _Systematic Phylogeny_, to give a comprehensive statement of the results attained. My chief aim was, on the one hand, to construct a natural system of organisms on the basis of their ancestral history, and on the other hand to prove the mechanical character of the phylogenetic process. All the activities of organisms which are at work in the transformation of species and the production of new ones in the struggle for existence may be reduced to their physiological functions--to growth, nutrition, adaptation, and heredity; and these again to the mechanics and chemistry of the plasm. The struggle for life is itself a mechanical process, in which natural selection uses the disproportion between the excess of germs and the restricted means of existence, in conjunction with the variability of species, in order to produce new purposive structures mechanically and without any preconceived design. This teleological mechanicism has no need of a mysterious design or finality; it takes its place in the general order of mechanical causality which controls all the processes in the universe. Natural finality is only a special instance of mechanical causality. The one is subordinate to the other, not opposed to it, as Kant would have it.

The effort that the great Lamarck made in 1809, in his _Philosophie Zoologique_, to establish transformism deserves high appreciation from monists, because it was the first attempt to give a natural explanation of the origin of the countless species of organic forms which inhabit our planet. Up to that time it had been the fashion to attribute their origin to a miraculous intervention of the Creator. This metaphysical creationism had now to face physical evolutionism. Lamarck explained the gradual formation of organic species by the interaction of two physiological functions--adaptation and heredity. Adaptation consists in the improvement of organs by use, and degeneration by disuse; heredity acts by transmitting the features thus acquired to posterity. New species arise by physiological transformation from older species. The fact that this great thought was overlooked for half a century does not detract from its profound significance. But it only obtained general recognition when Darwin had supplemented it and filled up its causal gaps by the theory of selection in 1859. Apart from this specifically Darwinian feature (whether it be true or not), the fundamental idea of transformism is now generally received; it is admitted to-day even by metaphysicians who maintained a spirited opposition to it thirty years ago. The fact of the progressive modification of species is only intelligible on Lamarck's theory that the actual species are the transformed descendants of older species. In spite of all the learning and zeal with which the theory has been attacked, it has proved irrefutable; nor can any one suggest a better theory to replace it. This may be said particularly of its chief consequence--the descent of man from a series of other mammals (proximately from the apes).

The high value of Darwin's theory of selection for the monistic biology is now acknowledged by all competent and impartial authorities on the science. In the course of the forty-four years since it found its way into every branch of biology, it has been employed in more than a hundred large works and several thousand essays in explaining biological phenomena. This alone is enough to show its profound importance. Hence it is mere ignorance of the subject and its literature to say, as has been done several times of late, that Darwinism is in decay, or even "dead and buried." However, absurd writings of this kind (such as Dennert's _At the Death-bed of Darwinism_) have a certain practical influence, because they fall in with the prevailing superstition in theology and metaphysics. Unfortunately, they also seem to obtain notice from the circumstance that a few botanists persistently attack the Darwinian theory. One of the most conspicuous of these is Hans Driesch, who affirms that all Darwinists (and therefore the great majority of modern biologists) have softening of the brain, and that Darwinism is (like Hegel's philosophy) the delusion of a generation. The arrogance of this conceited writer is about equal to the obscurity of his biological opinions, the confusion of which is covered by a series of most extravagant metaphysical speculations. All these attacks have lately been met very ably by Plate in his work, _On the Significance of the Darwinian Principle of Selection and the Problem of the Foundation of Species_ (second edition, 1903). The most thorough of recent defences of Darwinism is that made by August Weismann in his _Lectures on the Theory of Descent_ (1902) and other works. But the distinguished zoologist goes too far when he seeks to prove the omnipotence of selection and wishes to ground it on an untenable molecular hypothesis--the theory of germ-plasm, which we will consider presently. Apart from these or other exaggerations, we may say with Weismann that Lamarck's theory of descent received a sound causal basis by Darwin's theory of selection. Its real foundations are these three phenomena: heredity, adaptation, and the struggle for existence. All three are, as I have often said, of a purely mechanical and not a teleological nature. Heredity is closely bound up with the physiological function of reproduction, and adaptation with nutrition; the struggle for life follows logically and mathematically from the disproportion between the number of potential individuals (germs) and of actual individuals that grow to maturity and propagate the species.

When I had, in my _General Morphology_, endeavored to gain acceptance for Darwin's theory of selection, and had presented evolution as a comprehensive theory from the point of view of the monistic philosophy, a number of works, sometimes of value, appeared, which made special studies of the various parts of the immense province. Eighteen years afterwards a greater work was published, which started from the same monistic principles, but reached the same conclusion by a different way. In 1884 Carl Nägeli, one of our ablest and most philosophic botanists, issued his _Mechanical-physiological Theory of Evolution_. This interesting book consists of various parts. It is especially notable that evolution is presented in it as the one possible and natural theory of the origin of species; even morphology and classification are treated explicitly as "phylogenetic sciences." The chapter on archigony--a dark and dangerous problem that is generally avoided by scientists!--is one of the best that has been written on the subject. On the other hand, Nägeli rejects Darwin's theory of selection altogether, and would explain the origin of species by an inner "definitely directed variation," independently of the conditions of existence in the outer world. As Weismann has properly observed, this internal principle of evolution, which dispenses with adaptation in the true sense of the word, is at the bottom merely a "phyletic vital force." It is not made more acceptable by Nägeli when he builds up a subtle metaphysical system on it and postulates a special "principle of isagitation." But the idioplasm theory he connects with it is of some value, since it goes more fully into the differentiation of the cell-plasm into two physiologically different parts--the idioplasm of the hereditary matter and the trophoplasm as nutritive matter of the cell.

The vitalist and teleological idea of an internal principle of evolution, that determines the origin of animal and plant species independently of the environment and its conditions, is not only found in the "mechanical-physiological" theory of Nägeli, but also in several other attempts to explain the agencies of the transformation of species. All these efforts are welcomed by the academic philosophers with their Kantist dualism (mechanicism on the right, teleology on the left), and who are particularly anxious to save the supernatural element, Reinke's "cosmic intelligence," or the wisdom of the Creator, or the divine creative thought. All these dualistic and teleological efforts have the same fault: they overlook, or fail to appreciate properly, the immense influence of the environment on the shaping and modification of organisms. When, moreover, they deny progressive heredity and its connection with functional adaptation, they lose the chief factor in transformation. This applies also to the theory of germ-plasm.

The desire to penetrate deeper into the mysterious processes that take place in the plasm in the physiological activities of heredity and adaptation has led to the formulation of a number of molecular theories. The chief of these are the pangenesis theory of Darwin (1878), my own perigenesis theory (1876), the idioplasm theory of Nägeli (1884), the germ-plasm theory of Weismann (1885), the mutation theory of De Bries, etc. As I have already dealt with these in the sixth chapter (as well as in the ninth chapter of the _History of Creation_), I may refer the reader thereto. None of these or similar attempts has completely solved the very difficult problems in question, and none of them has been generally received. There is, however, one of them that we must consider more closely, because it is not only regarded by many biologists as the greatest advance of the theory of selection since Darwin, but it also touches the roots of several of the chief problems of biogeny. I mean the much-discussed germ-plasm theory of August Weismann (of Freiburg), one of our most distinguished zoologists. He has not only promoted the theory of descent by his many writings during the last thirty years, but has also put in its proper light the great importance and entire accuracy of the theory of selection. But, in his efforts to provide a molecular-physiological basis for it, he has proceeded by way of metaphysical speculation to frame a quite untenable theory of the plasm. While fully recognizing the ability and consistency and the able treatment which Weismann has shown, I am compelled once more to dissent from him. His ideas have recently been completely refuted by Max Kassowitz (1902) in his _General Biology_, and Ludwig Plate in the work I mentioned on the Darwinian principle of selection. We need not go into the details of the complicated hypothesis as to the molecular structure of the plasm which Weismann has framed in support of his theory of heredity--his theory of biophora, determinants, ideas, etc.--because they have no theoretical basis and are of no practical use. But we must pass some criticism on one of their chief consequences. In the interest of his complicated hypotheses, Weismann denies one of Lamarck's most important principles of transmutation--namely, the inheritance of acquired characters.

When I made the first attempt in 1866 to formulate the phenomena of heredity and adaptation in definite laws and arrange these in series, I drew a distinction between conservative and progressive heredity (chapter ix., _History of Creation_). Conservative heredity, or the inheritance of inherited characters, transmits to posterity the morphological and physiological features which each individual has received from his parents. Progressive heredity, or the inheritance of acquired characters, transmits to offspring a part of those features which were acquired by the parents in the course of their individual lives. The chief of these are the characters that are caused by the activity of the organs themselves. Increase in the use of the organs causes a greater access of nourishment and promotes their growth; decrease in the exercise of organs has the contrary effect. We have examples at hand in the modification of the muscles or the eyes, the action of the hand or throat in painting or singing, and so on. In these and all the arts the rule is: Practice makes perfect. But this applies almost universally to the physiological activity of the plasm, even its highest and most astounding function--thought; the memory and reasoning capacity of the phronema are improved by constant exercise of the cells which compose this organ, just as we find in the case of the hands and the senses.

Lamarck recognized the great morphological significance of this physiological use of the organs, and did not doubt that the modification caused was transmitted to offspring to a certain extent. When I dealt with this correlation of direct adaptation and progressive heredity in 1866, I laid special stress on the "law of cumulative adaptation" (_General Morphology_, ii., p. 208). "All organisms undergo important and permanent (chemical, morphological, and physiological) changes when acted on by a change in its life-conditions, slight in itself, but continuing for a long time or being frequently repeated." At the same time I pointed out that in this case two groups of phenomena are closely connected which are often separated--namely, cumulative heredity: firstly _external_, by the action of the external conditions (food, climate, environment, etc.), and secondly _internal_, by the reaction of the organism, the influence of internal conditions (habit, use and disuse of organs, etc.). The action of outer influences (light, heat, electricity, pressure, etc.) not only causes a reaction of the organism affected (energy of movement, sensation, chemosis, etc.), but it has an especial effect as a trophic stimulus on its nutrition and growth. The latter element has been particularly studied by Wilhelm Roux; his functional adaptation (1881) coincides with my cumulative adaptation, the close relation of which to correlative adaptation I had pointed out in 1866. Plate has recently given this "definitely directed variation" the name of ectogenetic orthogenesis, or, briefly, ectogenesis.

The controversy about progressive heredity still continues here and there. Weismann completely denies it, because he cannot bring it into harmony with his germ-plasm theory, and because he thinks there are no experimental proofs in support of it. A number of able biologists agree with him, led away by his brilliant argumentation. However, many of them foolishly lay great stress on experiments in heredity which prove nothing; for instance, the fact that the offspring of a mammal that has had its tail cut off do not inherit the feature. A number of recent observations seem to prove that in a few cases even defects of this sort (when they have caused profound and lasting disease of the part affected) may be transmitted to offspring. However, as far as the formation of new species is concerned, the fact is of no consequence; in this it is a question of cumulative or functional adaptation. Experimental proofs of this are difficult to find, if one wants a strict demonstration of the type of physical experiments; the biological conditions are generally too complicated and offer too many weak points to rigorous criticism. The beautiful experiments of Standfuss and C. Fisher (Zurich) have shown that changes in the environment (such as temperature or food) can cause striking modifications that are transmitted to offspring. In any case, there are plenty of luminous proofs of progressive heredity in the vast arsenal of morphology, comparative anatomy, and ontogeny.

Comparative anatomy affords a number of most valuable arguments for other phylogenetic questions as well as progressive heredity; and the same may be said of comparative anatomy and comparative ontogeny. I have collected and illustrated a good many of these proofs in the new edition of my _Anthropogeny_. However, in order to understand and appreciate them aright, the reader must have some acquaintance with the methods of critical comparison. This means not only an extensive knowledge of anatomy, ontogeny, and classification, but also practice in morphological thinking and reasoning. Many of our modern biologists lack these qualifications, especially those "exact" observers who erroneously imagine they can understand vast groups of phenomena by accurate description of detailed microscopic structures, etc. Many distinguished cytologists, histologists, and embryologists have completely lost the larger view of their work by absorption in these details. They even reject some of the fundamental ideas of comparative anatomy, such as the distinction between homology and analogy; Wilhelm His, for instance, declared that these "academic ideas" are "unreliable tools." On the other hand, physiological experiments ought to contribute to the solution of morphological problems, and of these they can say nothing. To show the incalculable value of comparative anatomy for phylogeny, I need only point to one of its most successful departments, the skeleton of the vertebrates, the comparison of the various forms of the skull, the vertebral column, the limbs, etc. It is not in vain that for more than a hundred years gifted scientists, from Goethe and Cuvier to Huxley and Gegenbaur, have devoted years of laborious research to the methodical comparison of these similar yet dissimilar forms. They have been rewarded by the discovery of the common laws of structure, which can only be explained in the sense of modern evolution by descent from common ancestors.

We have a striking example of this in the limbs of mammals, which, with the same internal skeletal structure, show a very great variety in outer form--the slender bones of the running carnivora and ungulates, the oar-bones of the whale and seal, the shovel-bones of the mole and hypudæus, the wings of the bat, the climbing bones of the ape, and the differentiated limbs of the human body. All these different skeletal forms have descended from the same common stem-form of the oldest Triassic mammals; their various forms and structures are adapted in scores of ways to different functions; but they rise _through_ these functions, and all these functional adaptations can only be understood by progressive heredity. The theory of germ-plasm gives no causal explanation whatever of them.

The majority of recent biologists are of opinion that of the two chief constituents of the nucleated cell the cytoplasm of the cell-body discharges the function of nutrition and adaptation, while the caryoplasm of the nucleus accomplishes reproduction and heredity. I first advanced this view in the ninth chapter of the _General Morphology_ (in 1866); and it was afterwards solidly and empirically established by the excellent investigations of Eduard Strasburger, the brothers Oscar and Richard Hertwig, and others. The elaborate finer structures which these observers discovered in cell-division led to the theory that the colorable part of the nucleus, chromatin, is the real hereditary matter, or the material substratum of the energy of heredity. Weismann added the theory that this germ-plasm lives quite separately from the other substances in the cell, and that the latter (the soma-plasm) cannot transmit to the germ-plasm the characters it has acquired by adaptation. It is on the strength of this theory that he opposes progressive heredity. The representatives of the latter (including myself) do not accept this absolute separation of germ-plasm from body-plasm; we believe that even in the process of cell-division in the unicellular organism there is partial blending of the two kinds of plasm (caryolysis), and that in the multicellular organism of the histona also the harmonious connection of all the cells by their plasma-fibres makes it possible enough for all the cells in the body to act on the germ-plasm of the germ-cells. Max Kassowitz has shown how we can explain this influence by the molecular structure of the plasm.

At the beginning of the twentieth century a new biological theory aroused a good deal of interest, and was welcomed by some as an experimental refutation of Darwin's theory of selection and by others as a valuable supplement to it. The distinguished botanist Hugo de Bries (of Amsterdam) gave an interesting lecture at the scientific congress at Hamburg in 1901 on "The Mutations and Mutation-periods in the Origin of Species." Supported by many years of experiments in selection and some ingenious speculations, he thinks he has discovered a new method of the transformation of species, an abrupt modification of the specific form at a bound, and so discredited Darwin's theory of their gradual change through long periods of time. In a large work on _Experiments and Observations on the Origin of Species in the Plant Kingdom_ (1903), De Bries has endeavored to demonstrate the truth of his theory of mutation. The warm approval which it won from a number of eminent botanists, and especially vegetal physiologists, was not shared by zoologists. Of these Weismann, in his _Lectures on the Theory of Descent_ (1902, ii. p. 358), and Plate in his _Problems of Species-formation_ (1903, p. 174), have dealt fully with the theory of mutation, and, while appreciating the interesting observations and experiments of De Bries, have rejected the theory he has built on them. As I share their opinion, I may refer the reader who is interested in these difficult problems to their works, and will restrict myself here to the following observations. The chief weakness of the theory of mutation of De Bries is on its logical side, in his dogmatic distinction between species and variety, mutation and variation. When he holds the constancy of species as a fundamental "fact of observation," we can only say that this (relative) permanence of species is very different in the different classes. In many classes (for instance, insects, birds, many orchids and graminea) we may examine thousands of specimens of a species without finding any individual differences; in other classes (such as sponges, corals, in the genera _rubus_ and _hieracium_) the variability is so great that classifiers hesitate to draw up fixed species. The marked difference between various forms of variability which De Bries alleges cannot be carried through; the fluctuating variations (which he takes to be unimportant) cannot be sharply distinguished from the abrupt mutations (from which new species are supposed to result at a bound). De Bries's mutations (which I distinguished in the _General Morphology_ as "monstrous changes" from other kinds of variation) must not be confused with the paleontological mutations of Waagen (1869) and Scott (1894) which have the same name. The sudden and striking changes of habit which De Bries observed only in one single species of _œnothera_ very rarely occur, and cannot be regarded as common beginnings of the formation of new species. It is a curious freak of chance that this species bears the name _œnothera Lamarckiana_; the views of the great Lamarck on the powerful influence of functional adaptation have not been refuted by De Bries. It must be carefully noted, in fact, that De Bries is firmly convinced of the truth of Lamarck's theory of descent, like all competent modern biologists. This must be well understood, because recent metaphysicians see in the supposed refutation of Darwinism the death of the whole theory of transformism and evolution. When they appeal in this sense to its most virulent opponents, Dennert, Driesch, and Fleischmann, we may remind them that the curious sermons of these minor sophists are no longer noticed by any competent and informed scientist.

Not only in the brilliant speculations of De Bries and Nägeli, but also in many other botanical works that have lately attempted to advance the theory of descent, we find a striking difference from the prevailing views of zoologists in the treatment of a number of general biological problems. This difference is, of course, not due to a disproportion of ability in the two great and neighboring camps of biology, but to the differences in the phenomena that we observe in plant life on the one hand and animal life on the other. It must be noted particularly that the organism of the higher animals (including our own) is much more elaborately differentiated in its various organs and much more exposed to our direct experience than that of the higher plants. The chief properties and activities of our muscles, skeleton, nerves, and sense-organs, are understood at once in comparative anatomy and physiology. The study of the corresponding phenomena in the bodies of the higher plants is much more difficult. The features of the innumerable elementary organs in the cell-monarchy of the animal body are much more intricate, yet at the same time much more intelligible, than those of the cell-republic of the higher plant-body. Thus the phylogeny of the plants encounters much greater difficulties than that of the animals; the embryology of the former says much less in detail than that of the latter. We can understand, therefore, why the biogenetic law is not so generally recognized by botanists as by zoologists. Paleontology, which provides such valuable fossil material for many groups of the animal kingdom that we can more or less correctly draw up their ancestral tree on the strength of this, gives us very little for most groups of the plant kingdom. On the other hand, the large and sharply demarcated plant-cell, with its various organella, is much more valuable in connection with many problems than the tiny animal-cell. For many physiological purposes, in fact, the higher plant body is more accessible to exact physical and chemical research than the higher animal body. The antithesis is less in the kingdom of the protists, as the difference between animal and vegetal life is mostly confined to difference of metabolism, and finally disappears altogether in the province of the unicellular forms of life. Hence, for a clear and impartial treatment of the great problems of biology, and especially of phylogeny, it is imperative to have a knowledge of both zoological and botanical investigation. The two great founders of the theory of descent--Lamarck and Darwin--were able to penetrate so deeply into the mysteries of organic life and its development because they had extensive attainments both in botany and zoology.

Of the various tendencies that have recently made their appearance among zoologists and botanists in the discussion of the theory of descent, we frequently find Neo-Lamarckism and Neo-Darwinism distinguished as opposing schools. This opposition has no meaning unless we understand by it the alternatives of transformism--with or without the theory of selection. The one principle that distinguishes Darwinism proper from the older Lamarckism is the struggle for existence and the theory of selection based on it. It is quite wrong to make the test an acceptance or rejection of progressive heredity. Darwin was just as firmly convinced as Lamarck or myself of the great importance of the inheritance of acquired characters, and particularly of the inheritance of functional adaptations; he merely ascribed to it a more restricted sphere of influence than Lamarck. Weismann, however, denies progressive heredity altogether, and wants to trace everything to "the omnipotence of natural selection." If this view of Weismann and the theory of germ-plasm he has based on it are correct, he alone has the honor of founding a totally new (and in his opinion very fruitful) form of transformism. But it is quite wrong to describe this Weismannism as Neo-Darwinism, as frequently happens in England. It is just as wrong to call Nägeli, De Bries, and other modern biologists who reject selection Neo-Lamarckists.

If the theory of descent is right, as all competent biologists now admit, it puts on morphology the task of assigning approximately the origin of each living form. It must endeavor to explain the actual organization of each by its past, and to recognize the causes of its modification in the series of its ancestors. I made the first attempt to achieve this difficult task in founding stem-history or phylogeny as an independent historical science in my "General Evolution" (in the second volume of the _General Morphology_). With it I associated as a second and equally sound part ontogeny; I understood by this the whole science of the development of the individual, both embryology and metamorphology. Ontogeny enjoys the privileges (especially in the way of certainty) of a purely descriptive science, when it confines itself to the faithful description of the directly observed facts, either the embryonic processes in the womb or the later metamorphic processes. The task of phylogeny is much more difficult, as it has to decipher long-past processes by means of imperfect evidence, and has to use its documents with the utmost prudence.

The three most valuable sources of evidence in phylogeny are paleontology, comparative anatomy, and ontogeny. Paleontology seems to be the most reliable source, as it gives us tangible facts in the fossils which bear witness to the succession of species in the long history of organic life. Unfortunately, our knowledge of the fossils is very scanty and often very imperfect. Hence the numerous gaps in its positive evidence have to be filled up by the results of two other sciences, comparative anatomy and ontogeny. I have dealt fully with this in my _Anthropogeny_. As I have also spoken of the general features of these phyletic evidences in the sixteenth chapter of the _History of Creation_, I need do no more here than repeat that it is necessary to make equal and discriminating use of all three classes of documents if we are to attain the aim of phylogeny correctly. Unfortunately, this necessitates a thorough knowledge of all three sciences, and this is very rare. Most embryologists neglect paleontology, most paleontologists embryology, while comparative anatomy, the most difficult part of morphology, involving most extensive knowledge and sound judgment, is neglected by both. Besides these three sources of phylogeny there is valuable proof afforded by every branch of biology, especially by chorology, œcology, physiology, and biochemistry.

Although there has been very extensive phylogenetic research during the last thirty years, and it has yielded a number of interesting results, many scientists still seem to look on them with a certain distrust; some contest their scientific value altogether, and say that they are nothing but airy and untenable speculations. This is especially the case with many physiologists who look upon experiment as the only exact method of investigation, and many embryologists who think their sole task is description. In view of these sceptical strictures, we may recall the history and the nature of geology. No one now questions the great importance and the various uses of this science, although in it there is no possibility of directly observing the historical processes as a rule. No scientist now doubts that the three vast successive formations of the Mesozoic Period--the Triassic, Jurassic, and Cretaceous--have been formed from sea-deposits (lime, sandstone, and clay), though no one was a witness to the actual formation; no one doubts to-day that the fossil skeletons of fishes and reptiles which we find in these groups are not mysterious freaks of nature, but the remains of extinct fishes and reptiles that lived on the earth during those millions of years long ago. And when comparative anatomy shows us the genealogical connection of these related forms, and phylogeny (with the aid of ontogeny) constructs their ancestral trees, their historical hypotheses are just as sound and reliable as those of geology; the only difference is that the latter are much simpler, and thus easier to construct. Phylogeny and geology are, in the nature of the case, _historical sciences_.

Hypotheses are necessary in phylogeny and geology, where the empirical evidence is incomplete, as in every other historical science. It is no detraction from the value of these to urge that they are sometimes weak and have to be replaced by better and stronger ones. A weak hypothesis is always better than none. We must, therefore, protest against the foolish dread of hypotheses which is urged against our phylogenetic methods by the representatives of the exact and descriptive sciences. This shrinking from hypotheses often hides a defective knowledge of other sciences, an incapacity for synthetic thought, and a feeble sense of causality. The delusions into which it leads many scientists may be seen from the fact that chemistry, for instance, is reckoned an "exact" science; yet no chemist has ever seen the atoms and molecules of compounds with which he is occupied daily, or the complicated relations on the assumption of which the whole of modern structural chemistry is based. All these hypotheses rest on inferences, not on direct observation.

I have, from the first, insisted on the close causal connection between ontogeny and phylogeny, ever since I distinguished these two parts of biogeny in the fifth book of the _General Morphology_. I also laid stress on the mechanical character of these sciences, and endeavored to give a physiological explanation of their morphological phenomena. Until then embryology had been regarded as a purely descriptive science. Carl Ernst Baer, who had provided a solid foundation for it in his classic _Animal Embryology_ (1828), was convinced that all the phenomena of individual development might be reduced to the laws of growth; but he was quite unconscious of the real direction of this growth, its "purposiveness," the real causes of construction. The distinguished Würtzburg anatomist, Albert Kölliker, whose _Manual of Human Embryology_ (1859) gave the first comprehensive treatment of the science from the cellular point of view, adhered, even in the fourth edition (1884), to the opinion that "the laws of the development of the organism are still completely unknown." In opposition to this generally received opinion, I endeavored, in 1866, to prove that Darwin had, by his improvement of the theory of descent, not only solved the phylogenetic problem of the origin of species, but, at the same time, given us the key to open the closed doors of embryology, and to learn the causes of the ontogenetic processes as well. I formulated this view in the twentieth chapter of the _General Morphology_, in forty-four theses, of which I will quote only the following three: 1. The development of organisms is a physiological process, depending on mechanical causes, or physico-chemical movements. 40. Ontogenesis, or the development of the organic individual, is directly determined by phylogenesis, or the evolution of the organic stem (_phylon_) to which it belongs. 41. Ontogenesis is a brief and rapid recapitulation of phylogenesis, determined by the physiological functions of heredity and adaptation. The pith of my biogenetic principle is expressed in these and the remaining theses on the causal nexus of biontic and phyletic development. At the same time I make it quite clear that I reduce the physical process of ontogenesis, and also phylogenesis, to a pure mechanics of the plasm (in the sense of the critical philosophy).

The comprehensive fundamental law of organic development was briefly formulated by me in the fifth book of the _General Morphology_ and in the tenth chapter of the _History of Creation_ (developed more fully in the fourteenth chapter of the tenth edition, 1902). I afterwards sought to establish it securely in two different ways. In the first place, I proved in my _Studies of the Gastræa Theory_ (1872-1877) that in all the tissue-animals, from the lowest sponges and polyps to the highest articulata and vertebrates, the multicellular organism develops from the same primitive embryonic form (the _gastrula_), and that this is the ontogenetic repetition, in virtue of heredity, of a corresponding stem-form (the _gastræa_). In the second place, I made the first attempt in my _Anthropogeny_ (1874) to illustrate this recapitulation theory from the instance of our own human organism, by trying to explain the complex process of individual development, for the whole frame and every single part of it, by causal connection with the stem-history of our animal ancestors. In the latest edition of this monistic "ontogeny of man" I gave numbers of illustrations (thirty plates and five hundred engravings) of these intricate structures, and endeavored to make the subject still plainer by the addition of sixty genetic tables. I may refer the reader to this work,[10] and not dwell any further here on the biogenetic law, especially as one of my pupils, Heinrich Schmidt (of Jena), has recently described its biological significance and its earlier history and present position in a very clear and reliable little work (_Haeckel's Biogenetic Law and its Critics_). I will only add a word or two on the struggle that has taken place for thirty years over the complete or partial recognition of the biogenetic law, its empirical establishment, and its philosophic application.

In the very name, "fundamental law of biogeny," which I have given to my recapitulation theory, I claim that it is universal. Every organism, from the unicellular protists to the cryptogams and cœlenteria, and from these up to the flowering plants and vertebrates, reproduces in its individual development, in virtue of certain hereditary processes, a part of its ancestral history. The very word "recapitulation" implies a partial and abbreviated repetition of the course of the original phyletic development, determined by the "laws of heredity and adaptation." Heredity brings about the reproduction of certain evolutionary features; adaptation causes a modification of them by the conditions of the environment--a condensation, disturbance, or falsification. Hence I insisted from the first that the biogenetic law consists of two parts, one positive and palingenetic and the other restrictively negative and cenogenetic. _Palingenesis_ reproduces a part of the original history of the stem; _cenogenesis_ disturbs or alters this picture in consequence of subsequent modifications of the original course of development. This distinction is most important, and cannot be too often repeated in view of the persistent misunderstanding of my opponents. It is overlooked by those who (like Plate and Steinmann) grant it only a partial validity, and by those who reject it altogether (like Keibel and Hensen). The embryologist Keibel is the most curious of these, as he has himself afforded a good many proofs of the biogenetic law in his careful descriptive-embryological works. But he has so little mastered it that he has never understood the distinction between palingenesis and cenogenesis.

It is especially unfortunate that one of our most distinguished embryologists, Oscar Hertwig, of Berlin, who provided a good deal of evidence in favor of the biogenetic law thirty years ago, has lately joined the opponents of it. His supposed "correction" or modification of it is, as Keibel has rightly said, a complete abandonment of it. Heinrich Schmidt has partly explained the causes of this change in his work on the biogenetic law. They are not unconnected with the psychological metamorphosis which Oscar Hertwig has undergone at Berlin. In the discourse on "The Development of Biology in the Nineteenth Century," which he delivered at the scientific congress at Aachen in 1900, he openly accepted the dualist principles of vitalism (although he says they are "just as unreliable as the chemico-physical conception of the opposing mechanical school"). The views which he has lately advanced on the worthlessness of Darwinism and the unreliability of phylogenetic hypotheses are diametrically opposed to the opinions he represented at Jena twenty-five years ago, and to those which his brother, Richard Hertwig, of Munich, has consistently maintained in his admirable _Manual of Zoology_.

In opposition to the mechanical ontogeny which I formulated in 1866 and embodied in the biogenetic law, a number of other tendencies in embryology afterwards appeared, and, with the common title of "mechanical embryology," branched out in every direction. The chief of these to attract attention thirty years ago were the pseudo-mechanical theories of Wilhelm His, who has rendered great service to ontogeny by his accurate descriptions and faithful illustrations of vertebrate-embryos, but who has no idea of comparative morphology, and so has framed the most extraordinary theories about the nature of organic development. In his _Study of the First Sketch of the Vertebrate-body_ (1868), and many later works, His endeavored to explain the complicated ontogenetic phenomena on direct and simple physical lines by reducing them to elasticity, bending, folding of the embryonic layers, etc., while explicitly rejecting the phylogenetic method; he says that this is "a mere by-way, and quite unnecessary for the explanation of the ontogenetic facts (as direct consequences of physiological principles of development)." As a matter of fact, nature rather plays the part of an ingenious tailor in His's pseudo-mechanical and tectogenetic speculations, as I have shown in the third chapter of the _Anthropogeny_. Hence they have been humorously called the "tailor theory." However, they misled a few embryologists by opening the way to a direct and purely mechanical explanation of the complex embryonic phenomena. Although they were at first much admired, and immediately afterwards abandoned, they have found a number of supporters lately in various branches of embryology.

The great success that modern experimental physiology achieved by its extensive employment of physical and chemical experiments inspired a hope of attaining similar results in embryology by means of the same "exact" methods. But the application of them in this science is only possible to a slight extent on account of the great complexity of the historical processes and the impossibility of "exactly" determining historical matters. This is true of both branches of evolution, individual and phyletic. Experiments on the origin of species have very little value, as I said before; and this is generally true of embryological experiments also. However, the latter, especially careful experiments on the first stages of ontogenesis, have yielded some interesting results, particularly in regard to the physiology and pathology of the embryo at the earliest stages of development. The _Archiv für Entwickelungsmechanik_, which is edited by the chief representative of this school, Wilhelm Roux, contains, besides these valuable inquiries, a good number of ontogenetic articles, which partly rely on and partly ignore the biogenetic law.

Psychology and biogeny have been up to the present regarded as the most difficult branches of biology for monistic explanation, and the strongest supports of dualistic vitalism. Both departments become accessible to monism and a mechanico-causal explanation by means of the biogenetic law. The close correlation which it establishes between individual and phyletic development, and which depends on the interaction of heredity and adaptation, makes it possible to explain both. In regard to the first, I formulated the following principle thirty years ago in my first study of the gastræa theory: "Phylogenesis is the mechanical cause of ontogenesis." This single principle clearly expresses the essence of our monistic conception of organic development:

In the future every student will have to declare himself for or against this principle, if in biogeny he is not content with a mere admiration of the wonderful phenomena, but desires to understand their significance. The principle also makes clear the wide gulf that separates the older teleological and dualistic morphology from the modern mechanical and monistic science. If the physiological functions of heredity and adaptation are proved to be the sole causes of organic construction, every kind of teleology, and of dualistic and metaphysical explanation, is excluded from the province of biogeny. The irreconcilable opposition between the leading principles of the two is clear. Either there is or is not a direct and causal connection between ontogeny and phylogeny. Either ontogenesis is a brief compendium of phylogenesis or it is not. Either epigenesis and descent--or pre-formation and creation.

In repeating these principles here, I would lay stress particularly on the fact that, in my opinion, our "mechanical biogeny" is one of the strongest supports of the monistic philosophy.

XVII

THE VALUE OF LIFE

Changes of life--Aim of life--Progress of life--Historic aims--Historic waves--Value of life in classes and races of men--Psychology of uncivilized races--Savages--Barbarians--Civilized nations--Educated nations--Three stages of development (lower, middle, and higher) in each of the four classes--Individual and social value of civilized life in the five sections of nutrition, reproduction, movement, sensation, and mental life--Estimate of human life.

The value of human life is seen by us to-day, now that evolution is established, in quite a different light from fifty years ago. We are now accustomed to regard man as a natural being, the most highly developed natural being that we know. The same "eternal iron laws" that rule the evolution of the whole cosmos control our own life. Monism teaches that the universe really deserves its name, and is an all-embracing unified whole--whether we call it God or Nature. Monistic anthropology has now established the fact that man is but a tiny part of this vast whole, a placental mammal, developed from a branch of the order of primates in the later Tertiary Period. Hence, before we seek to estimate the value of man's life, we will cast a glance at the significance of organic life generally.

An impartial survey of the history of organic life on our planet teaches, first of all, that it is a process of constant change. Millions of animals and plants die every second, while other millions replace them; every individual has his definite period of life, whether it lives only a few hours, like the one-day fly or the infusorium, or, like the Wellingtonia, the dragon-tree of Orotava, and many other giant trees, lives for thousands of years. Even the species, the collection of like individuals, is just as transitory, and so are the orders and classes that embrace numbers of species of animals and plants. Most species are confined to a single period of the organic history of the earth; few species or genera pass unchanged through several periods, and not a single one has lived in all the periods. Phylogeny, taking its stand on the facts of paleontology, teaches unequivocally that every specific living form has only existed a longer or shorter period in the course of the many (more than a hundred) million years which make up the history of organic life.

Every living being is an end to itself. On this point all unprejudiced thinkers are agreed, whether, like the teleologist, they believe in an entelechy or dominant as regulator of the vital mechanism, or whether they explain the origin of each special living form mechanically by selection and epigenesis. The older anthropistic idea, that animals and plants were created for man's use, and that the relations of organisms to each other were generally regulated by creative design, is no longer accepted in scientific circles. But it is just as true of the species as of the individual that it lives for itself, and looks above all to self-maintenance. Its existence and "end" are transitory. The progressive development of classes and stems leads slowly but surely to the formation of new species. Every special form of life--the individual as well as the species--is therefore merely a biological episode, a passing phenomenal form in the constant change of life. Man is no exception. "Nothing is constant but change," said the old maxim.

The historical succession of species and classes is, both in the animal and the plant kingdom, accompanied by a slow and steady progress in organization. This is directly and positively taught by paleontology; its creation-medals, the fossils, are unequivocal and irrefutable witnesses to this phylogenetic advance. I have dealt with the subject in my _History of Creation_, and at the same time shown that both the progressive improvement and the increasing variety of the species can be explained mechanically as necessary consequences of selection. There was no need of a conscious Creator or a transcendental purposiveness to effect this. Scientific and thorough proof of this will be found in the three volumes of my _Systematic Phylogeny_ (1894). I need only refer briefly to the two conspicuous examples we have in the stem-history of the tissue-plants and that of the vertebrates. Of the metaphyta the ferns are the chief groups in the Paleozoic, the gymnosperms in the Mesozoic, and the angiosperms in the Cenozoic age. Of the vertebrates only fishes are found in the Silurian age, dipneusta only begin in the Devonian, and the first mammals are in the Triassic.

A number of false teleological conclusions have been drawn from these facts of progressive modification of forms, as they are given in paleontology. The latest and most developed form of each stem was taken to be the preconceived aim of the series, and its imperfect predecessors were conceived as preparatory stages to the attainment of this aim. It was like the conduct of many historians, who, when a particular race or state has reached a high rank in civilization as a result of its natural endowments and favorable conditions of development, hail it as a "chosen people," and regard its imperfect earlier condition as a deliberately conceived preparatory stage. In point of fact, these evolutionary stages were bound to proceed according as the internal structure (given by heredity) and the outer conditions (provoking adaptation) determined. We cannot admit any conscious direction to a certain end, either in the form of theistic predestination or pantheistic finality. For this we must substitute a simple mechanical causality in the sense of psycho-mechanical monism or hylozoism.

Although the stem-history of plants and animals, like the history of humanity, shows a progressive advance taken as a whole, we find a good deal of vacillation in detail. These historical waves are wholly irregular; in periods of decay the hollows of the waves often persist for a long time, and are then succeeded by a fresh rise to the crest of another wave. New and rapidly advancing groups come to take the place of the old decaying groups, bringing with them a higher stage of organization. Thus, for instance, the ferns of to-day are only a feeble survival of the huge and varied pteridophyta that formed the most conspicuous part of the paleozoic forests in the Devonian and Carboniferous periods; they were ousted in the Secondary Period by their gymnosperm descendants (cycadea and conifers), and these, again, in the Tertiary Period by the angiosperm flowering plants. So among the terrestrial reptiles the modern tortoises, serpents, crocodiles, and lizards are only a feeble remnant of the enormous reptile-fauna that dominated the Secondary Period, the colossal dinosauri, pterosauri, ichtyosauri, and plesiosauri. They were replaced in the Tertiary Period by the smaller but more powerful mammals. In the history of civilization the Middle Ages form a deep valley between the crests of the waves of classical antiquity and modern culture.

These few examples suffice to show that the various classes and orders of living things have a very different value when compared with each other. In regard to their intrinsic aim, self-maintenance, it is true that all organisms are on a level, but in their relations to other living things and to nature as a whole they are of very unequal value. Not only may larger animals and plants retain domination for a long time in virtue of their special use or superior force and mass, but small ones may prevail owing to their power of inflicting injury (bacteria, fungi, parasites, etc.). In the same way the value of the various races and nations is very unequal in human history. A small country like Greece has almost dominated the mental life of Europe for more than two thousand years in virtue of its superior culture. On the other hand, the various tribes of American Indians have, it is true, developed a partial civilization in some parts (Peru and Central America); but, on the whole, they have proved incapable of advancing.

Though the great differences in the mental life and the civilization of the higher and lower races are generally known, they are, as a rule, undervalued, and so the value of life at the different levels is falsely estimated. It is civilization and the fuller development of the mind that makes civilization possible, that raise man so much above the other animals, even his nearest animal relatives, the mammals. But this is, as a rule, peculiar to the higher races, and is found only in a very imperfect form or not at all among the lower. These lower races (such as the Veddahs or Australian negroes) are psychologically nearer to the mammals (apes or dogs) than to civilized Europeans; we must, therefore, assign a totally different value to their lives. The views on the subject of European nations which have large colonies in the tropics, and have been in touch with the natives for centuries, are very realistic, and quite different from the ideas that prevail in Germany. Our idealistic notions, strictly regulated by our academic wisdom and forced by our metaphysicians into the system of their abstract ideal-man, do not at all tally with the facts. Hence we can explain many of the errors of the idealistic philosophy and many of the practical mistakes that have been made in the recently acquired German colonies; these would have been avoided if we had had a better knowledge of the low psychic life of the natives (_cf._ the writings of Gobineau and Lubbock).

The grave errors that have been maintained in psychology for centuries are mostly due to a neglect of the comparative and genetic methods and the narrow employment of self-observation, or the introspective method; they are also partly due to the fact that metaphysicians generally make their own highly developed mind--a scientifically trained reason--the starting-point of their inquiry, and regard this as representative of the human mind in general, and thus build up their ideal scheme. The gulf between this thoughtful mind of civilized man and the thoughtless animal soul of the savage is enormous--greater than the gulf that separates the latter from the soul of the dog. Kant would have avoided many of the defects of his critical philosophy, and would not have formulated some of his powerful dogmas (such as the immortality of the soul, or the categorical imperative) if he had made a thorough and comparative study of the lower soul of the savage, and phylogenetically deduced the soul of civilized man therefrom.

The extreme importance of this comparison has only been fully appreciated of late years (by Lubbock, Romanes, etc.). Fritz Schultze (of Dresden) made the first valuable attempt in his interesting _Psychology of the Savage_ (1900) to give us an "evolutionary psychological description of the savage in respect of intelligence, æsthetics, ethics, and religion." At the same time, he gives us "a history of the natural creation of the human imagination, will, and faith." The first book of this important work deals with thought, the second with will, and the third with the religious ideas of the savage, or "the story of the natural evolution of religion" (fetichism, animism, worship of the heavenly bodies). In an appendix to the second book the author deals with the difficult problems of evolutionary ethics, supporting himself by the authority of the great work of Alexander Sutherland, _The Origin and Growth of the Moral Instinct_ (1898). Sutherland divides humanity, in regard to the various stages of civilization and mental development (not according to racial affinity), into four great classes: 1, Savages; 2, barbarians; 3, civilized races; 4, educated races. As this classification of Sutherland's not only enables us to take a good survey of the various forms of mental development, but is also very useful in connection with the question of the value of life at the different stages, I will briefly reproduce the chief points of his characterization of the four classes.

I. SAVAGES.--Their food consists of wild natural products (the fruits and roots of plants, and wild animals of all kinds). Most of them are, therefore, fishers or hunters. They are ignorant of agriculture and the breeding of cattle. They live isolated lives in families or scattered in small groups, and have no fixed home. The lowest and oldest savages come very close to the anthropoid apes from which they have descended, in bodily structure and habits. We may distinguish three orders in this class--the lower, middle, and higher savages.

_A._ Lower savages, approaching nearest to the ape, pygmies of small stature, four to four and a half feet high (rarely four and three-quarters); the women sometimes only three to three and a half feet. They are woolly haired and flat-nosed, of a black or dark brown color, with pointed belly, thin and short legs. They have no homes, and live in forests and caverns, and partly on trees; wander about in small families of ten to forty persons; quite naked, or with just a trace of some primitive garment. Of the lower races now living we must put in this class the Veddahs of Ceylon, the Semangs of the Malay Peninsula, the Negritos of the Philippines, the Andaman Islanders, the Kimos of Madagascar, the Akkas of Guinea, and the Bushmen of South Africa. Other scattered remnants of these ancient negroid dwarfs, which approach closely to the anthropoid apes, still live in various parts of the primitive forests of the Sunda Islands (Borneo, Sumatra, Celebes).

The value of the life of these lower savages is like that of the anthropoid apes, or very little higher. All recent travellers who have carefully observed them in their native lands, and studied their bodily structure and psychic life, agree in this opinion. Compare the thorough treatment of the Veddahs of Ceylon in the work of the brothers Sarasin (of which I have given a summary in my _Travels in Ceylon_). Their only interests are food and reproduction, in the same simple form in which we find these among the anthropoid apes (_cf._ chapters xv. and xxiii. of my _Anthropogeny_). Our own ancestors were probably much the same ten thousand or more years ago. On the strength of fossil remains of Pleistocene men Julius Kollmann has shown it to be very probable that similar dwarf races (with an average height of four and a half feet) inhabited Europe at that time.

_B._ Middle savages, somewhat larger and less apelike than the preceding, averaging five to five and a half feet in height. Their homes are rock caverns and shelters from the wind and rain. Though they have shirts and other rudiments of clothing, both sexes generally go naked; they have primitive weapons of wood and stone and rudely fashioned boats, wander in troops of fifty to two hundred, and have no social organization; certain races, however, have laws. To this group belong the Australian negroes and Tasmanians, the Ainos of Japan, the Hottentots, Fuegians, Macas, and some of the forest races of Brazil. The value of their life is very little superior to that of the preceding order.

_C._ Higher savages, mostly of average human height (smaller in colder regions), having always simple dwellings (generally of skins or the bark of trees). They have always primitive clothing, and good weapons of stone, bronze, or copper. They wander in troops of one hundred to five hundred, led by prominent but not ruling princes, and exhibiting rudimentary differences of rank. The method of life is determined by hereditary customs. To this group belong many of the primitive inhabitants of India (Todas, Nagas, Curumbas, etc.), the Nicobar Islanders, the Samoyeds, and Kamtschadals; in Africa, the negroes of Damara; and most of the Indian tribes of North and South America. Their life is higher than that of the pithecoid lower and middle savages, but less than that of the barbarians.

II. BARBARIANS OR SEMI-SAVAGES.--The greater part of their food consists of natural products, which they secure with some foresight; hence they have developed agriculture and pasture to a greater or less extent. The division of labor is slight, each family supplying its own wants. As a rule, a stock of food is provided for the whole year. As a result of this, art begins to develop. They have generally fixed dwellings.

_A._ Lower Barbarians. Dwellings: Simple huts, generally grouped into villages and surrounded with plantations. Clothing worn regularly, but very simple: the men often naked in hot climates or with shirt. Pottery and cooking utensils, tools of stone, wood, or bone. Rudiments of commerce by exchange. Groups of one thousand to five thousand persons able to form larger communities; distinctions of rank and warfare. Princes rule according to traditional laws. Of this group we have in Asia many of the aboriginal inhabitants of India (Mundas, Khonds, Paharias, Bheels, etc.), the Dyaks of Borneo, the Battaks of Sumatra, Tunguses, Kirgises, etc.; in Africa the Kaffirs, Bechuanas, and Basutos; in Australasia the aborigines of New Guinea, New Caledonia, New Hebrides, New Zealand, etc.; and in America the Iroquois and Thlinkets, and the inhabitants of Nicaragua and Guatemala.

_B._ Middle barbarians. Dwellings good and durable, generally of wood, roofed with cane or straw, forming fine towns. Clothing general, though nudity is not considered immoral. Pottery, weaving, and metal-work pretty well developed. Commerce in regular markets, with the use of money. States ruled by kings in accordance with traditional laws, fixed distinctions of rank, communities up to one hundred thousand persons. To these belong in Asia the Calmucks; in Africa many negro races (Ashantis, Fantis, Fellahs, Shilluks, Mombuttus, Owampos, etc.); in Polynesia the inhabitants of the Fiji, Tonga, Samoa, and Markesas islands. In Europe the Lapps belonged to this class two hundred years ago, the ancient Germans two thousand years ago, the Romans before Numa, and the Greeks of the Homeric period.

_C._ Higher barbarians. Dwellings, usually solid stone buildings. Clothing obligatory, weaving habitual occupation of the women, metal-work far advanced, tools generally of iron. Restricted commerce, with minted money, no rudder-ships. Crude judicature in fixed courts; rudimentary writing. Masses of people, with progressive division of labor and hereditary distinctions of rank, sometimes reaching half a million souls, under an autonomous ruler. To this class belong in Asia most of the Malays (in the large Sunda Islands and the peninsula of Malacca), and the nomadic races of Tartars, Arabs, etc.; in Polynesia the islanders of Tahiti and Hawaii; in Africa the Somalis and Abyssinians, and the inhabitants of Zanzibar and Madagascar. Of the historic peoples of antiquity we have the Greeks of the time of Solon, the Romans at the beginning of the republic, the Jews under the Judges, the Anglo-Saxons of the Heptarchy, and the Mexicans and Peruvians at the time of the Spanish invasion.

III. CIVILIZED RACES.--Food and complex vital needs are easily satisfied on account of the advanced division of labor and improvement of instruments. Art and science are consequently developed more and more. The increasing specialization brings about a great elaboration of individual functions, and at the same time a great strengthening of the whole body politic, as there is complete mutual dependence. The citizens see that they must submit to the laws of the state.

_A._ Lower civilized races. Towns with stone walls; vast architectural works in stone; use of the plough in agriculture. War is intrusted to a particular class. Writing firmly established, primitive law-books, fixed courts. Literature begins to develop. To this group belong in Asia the inhabitants of Thibet, Bhutan, Nepaul, Laos, Annam, Korea, Manchuria, and the settled Arabs and Turcomans; in Africa the Algerians, Tunisians, Moors, Kabyles, Tuaregs, etc. Of historical races we have the ancient Egyptians, Phœnicians, Assyrians, Babylonians, Carthaginians, the Greeks after Marathon, the Romans of the time of Hannibal, and the English under the Norman kings.

_B._ Middle civilized races. Beautiful temples and palaces, built of stone and brick. Windows come into use, and sailing-ships. Commerce expands. Writing and written books are general; the literary instruction of the young is attended to. Militarism is further developed; so are legislation and advocacy. Of these we have in Asia the Persians, Afghans, Birmans, and Siamese; in Europe the Finns and Magyars of the eighteenth century. Of historical peoples we must count among them the Greeks of the age of Pericles, the Romans of the later republic, the Jews under the Macedonian rule, France under the first Capets, and England under the Plantagenets.

_C._ Higher civilized races. Stone houses general; streets paved; chimneys, canals, water and wind mills. Beginnings of scientific navigation and warfare. Writing general, written books widely distributed, literature esteemed. The highly centralized state embraces communities of ten millions or more. Fixed and written codes of law are officially promulgated and applied by courts to particular cases. Numbers of government officials have settled rank. To this group belong in Asia the Chinese, Japanese, and Hindoos; also the Turks and the various republics of South America, etc. In history we have the Romans of the empire, and the Italians, French, English, and Germans of the fifteenth century.

IV. CULTIVATED RACES.--Food and other needs are artificially supplied with the greatest ease and in abundance, human labor being replaced by natural forces. The social organization grows and facilitates the play of all the social forces, and man obtains a great freedom to cultivate his mental and æsthetic qualities. Printing is in general use, the education of the young one of the first duties. War becomes less important; rank and fame depend less on military bravery than on mental superiority. Legislation is influenced by representatives of the people. Art and science are increasingly promoted by state aid.

Alexander Sutherland distinguishes three stages of development--the lower, middle, and higher--in the fourth as well as in the preceding classes. To the first stage he assigns "the leading nations of Europe and their offshoots, such as the United States of North America." For the second stage--middle cultured races--he gives a programme that may be carried out in three or four hundred years' time, with this definition: "All men are well fed and housed; war is universally condemned, but breaks out now and again. Small armies and fleets of all the nations co-operate as a sort of international police; commercial and industrial life are directed according to the moral precepts of sympathy; culture is general; crime and punishment rare." Of the third and highest stage Sutherland merely says, "Too bold a subject for prophecy, that may not come for one thousand to two thousand years yet." This division seems to me too vague and unsatisfactory, in the sense that it does not properly emphasize the civilization of the nineteenth century in contrast with all preceding stages. It would be better to distinguish _provisionally_ the following stages in modern civilization: first, sixteenth to eighteenth century; second, nineteenth century; and third, twentieth century and the future.

_A._ Lower cultured races (Europe, sixteenth to eighteenth century). At the commencement of this period, the first half of the sixteenth century, we notice the preparatory movements to the full growth of mental life which was to achieve such great results in the following periods: 1. The cosmic system of Copernicus (1543) maintained by Galileo (1592). 2. The discovery of America by Columbus (1492) and of the East Indies by Vasco da Gama (1498), the first circumnavigation of the earth by Magellan (1520) and the evidence it afforded of the rotundity of the earth. 3. The liberation of the mind of Europe from the papal yoke by Martin Luther (1517) and the repulse of the prevailing superstition by the spread of the Reformation. 4. The new impulse to scientific investigation independently of scholasticism and the Church and of the philosophy of Aristotle; the founding of empirical science by Francis Bacon (1620). 5. The spread of scientific knowledge by the press (Gutenberg, 1450) and wood-engraving. The way was prepared for modern civilization by these and other advances in the sixteenth century, and it quickly arose above the barbaric level of the Middle Ages. However, it was confined at first within narrow limits, as the reactionary civilization of the Middle Ages was still powerful in political and social life, and the struggle against superstition and unreason made slow progress. The French Revolution (1792) at last gave a great impetus in practical directions.

_B._ Middle cultured races. This name may be given to the leading nations of Europe and North America in the nineteenth century. We may illustrate in the following achievements the great advance which this "century of science" made as compared with all preceding ages: 1. Deepening, experimental grounding, and general spread of a knowledge of nature; independent establishment of many new branches of science; founding of the cell-theory (1838), the law of energy (1845), and the theory of evolution (1859). 2. Practical and comprehensive application of this theoretical science to all branches of art and industry. Especially 3. The overcoming of time and space by the extraordinary speed of transit (steamboats, railways, telegraphs, electrotechnics). 4. Construction of the monistic and realistic philosophy, in opposition to the prevailing dualistic and mystical views. 5. Increasing influence of rational scientific instruction and abandonment of the religious fiction of the Churches. 6. Increasing self-consciousness of the nations on account of having a share in government and legislation; extinction of the belief in the divine right of rulers. New distinction of classes. However, these great advances, to which we children of the nineteenth century may point with pride, are far from being universal; they are struggling daily with reactionary views and powers in Church and state, with militarism, and with ancient and venerable immorality of every kind.

_C._ The higher culture which we are just beginning to glimpse will set itself the task of creating as happy and contented a life as possible for all men. A perfect ethic, free from all religious dogma and based on a clear knowledge of natural law, will be found in the golden rule, "Love thy neighbor as thyself." Reason tells us that a perfect state must provide the greatest possible happiness for every individual that belongs to it. The adjustment of a rational balance between egoism and altruism is the aim of our monistic ethics. Many barbaric customs that are still regarded as necessary--war, duelling, ecclesiastical power, etc.--will be abolished. Legal decisions will suffice to settle the quarrels of nations, as they now do of individuals. The chief interest of the state will be, not the formation of as strong a military force as possible, but the best possible instruction of its young, with special attention to art and science. The improvement of technical methods, owing to new discoveries in physics and chemistry, will bring greater satisfaction of our needs of life. The artificial production of albumin will provide plenty of food for all. A rational reform of the marriage relations will increase the happiness of family life.

The darker sides of modern life, of which we are all more or less sensitive, have been laid bare by Max Nordau in his _Conventional Lies of Civilization_. They will be greatly altered if reason is permitted to have its way in practical life, and the present evil customs, based on antiquated dogmas, are suppressed. But, in spite of all these shades, the luminous features of modern civilization are so great that we look to the future with hope and confidence. We need only glance back half a century, and compare life to-day with what it was then, in order to realize the progress made. If we regard the modern state as an elaborate organism (a "social individual of the first order"), and compare its citizens to the cells of a higher tissue-animal, the difference between the state of to-day and the crudest family groups of savages is not less than that between a higher metazoon (such as a vertebrate) and a cœnobium of protozoa. The progressive division of labor, on the one hand, and the centralization of society, on the other, prepare the social body for higher functions than in isolation, and proportionately increase the worth of its life. To see this more clearly, let us compare the personal and the social value of life in the five chief fields of vital activity--nutrition, reproduction, movement, sensation, and mental life.

The first need of the individual organism, self-maintenance, is met in a much more perfect manner in the modern state than it was formerly. The savage is satisfied with the raw products of nature--with hunting, fishing, and the gathering of roots and fruits. Agriculture and pasturage come later. Many stages of barbarism and lower civilization must be passed before the conditions of feeding, housing, and clothing provide a secure and comfortable existence for man, and permit the addition of æsthetic and intellectual interests to the indispensable search for food.

The feeding and condition of the social body as a whole have been improved by modern civilization, just as in the case of the individual. The progress of chemistry and agriculture has enabled us to produce food in larger quantities. The ease and rapidity of transfer allow it to be distributed over the whole earth. Scientific medicine and hygiene have discovered many means of diminishing the dangers of disease and preventing its occurrence. By means of public baths, gymnasiums, popular restaurants, public gardens, etc., greater care is taken of the health of the community. The arrangement of modern houses and their heating and lighting have been immensely improved. Modern social politics strives more and more to extend these benefits of civilization to the lower classes. Philanthropic societies are busy supplying the material and spiritual wants of various classes of sufferers. It is true there is still a broad margin for the improvement of the national well-being. But, on the whole, it cannot be denied that the provision of food in the modern state is an immense advance upon that of the Middle Ages and of the barbaric period.

The great value of modern civilization and its vast progress beyond the condition of the savage is seen in no branch of physiology so conspicuously as in the wonderful process of reproduction and the maintenance of the species. In most savages and barbarians the satisfaction of their powerful sexual impulse is at the same low stage as in the ape and other mammals. The woman is merely an object of lust to the man, or even a slave without rights, bought and exchanged like all other property. Improvement is slow and gradual in the value of this property, until it reaches a high guarantee of permanency in the formal marriage. The family life proves a source of higher and finer enjoyment for both parties. The position of woman advances with civilization; her rights obtain further recognition, and in addition to sensual love the psychic relation of man and wife begins to develop. The common concern for the proper care and education of the children, which we find to an extent even in the case of many animals, leads to the further development of family life and the founding of the school. With the advent of a higher stage of civilization begins the refinement of sexual love, which finds its highest satisfaction, not in the momentary gratification of the sex-impulse, but in the spiritual relation of the sexes and their constant and intimate intercourse. The beautiful then unites with the good and the true to form a harmonious trinity. Hence love has been for thousands of years the chief source of the æsthetic uplifting of man in every respect; the arts--poetry, music, painting, and sculpture--have drawn inexhaustively from this source. However, for the individual civilized human being this higher love is of value, not only because it satisfies the natural and irresistible sex-impulse in its noblest form, but also because the mutual influence of the sexes, their complementary qualities and their common enjoyment of the highest ideal good, has a great effect upon individual character. A good and happy marriage--which is not very common to-day--ought to be regarded, both psychologically and physiologically, as one of the most important ends of life by every individual of the higher nations.

As a pure marriage is the best form of family life and the most solid foundation of the state, its high social value is at once evident. The attraction and mutual devotion of the sexes fulfils in the highest degree the ethical golden rule--the balance of egoism and altruism. As Fritz Schultze very truly says in his _Comparative Psychology_

We must not seek the causes of this altruism in the transcendental region of the supernatural, or in any metaphysical abstraction, but must go back to the very real and natural qualities of the organic being--and then there can be no question that the organic sex-impulse, at once physical and psychical is the first and enduring source of all love, however spiritual, and of all real ethical and sympathetic feelings and the morality founded thereon. There are two primitive instincts in all organisms: that of self-maintenance and that of the maintenance of the species. The one is the strong impulse of egoism, the other the spring of altruism: from the one come all unfriendly and from the other all friendly feelings. Every being seeks first to nourish and protect itself in virtue of its instinct of self-maintenance. But soon the magic of the instinct for the maintenance of the species works in it; it feels the sex-impulse, and thinks it is only satisfying its egoistic lust in yielding to it. In this it is wrong; it is not really serving itself, but the whole, the species, the genus. The ardor of love burns in it; and however sensual this love is at first, the new feeling is undeniably a feeling of belonging to another and of mutual consideration, looking not only to itself, but to another; not only to its own good, but to that of another, and finding its own good only in that of the other. And though this feeling at first only unites the two parents, it enlarges when children enter into life, and is extended to them in the form of parental love. Thus, out of the sex-impulse of the maintenance of the species, with its strong physical and psychic roots, is developed the love of spouses, of parents, of children, and of neighbor. Disinterested egoism goes even to the extent of sacrificing its own life for its young; in this organic and natural family love, and in the sense of the family that comes of it, we find the roots of all sympathetic and really ethical altruistic feelings; from this it widens out to larger spheres. Hence, the family is rightly held to be the chief source of all real moral feeling and life, not only in the human, but also in the animal world.

The further ennoblement of family life in the advance of civilization will give fresh proofs of the truth of this appreciation.

We now turn to consider the advantages that modern civilization offers in the way of movement in contrast to the simple methods of locomotion of the savage. We may point out first that the earliest men, like their ancestors, the anthropoid apes, lived in trees, and only gradually began to run on the ground. Some of the higher savages began to use the horse for riding and to tame it. Many inhabitants of the coast or islands began at an early period to make boats. Later the barbaric tribes invented the wagon, and much later again streets were paved and vehicles improved by civilized races. But the nineteenth century brought the invaluable means of rapid and convenient travelling by means of steamboats and railways. The whole problem of transit was revolutionized, and in the last few decades further vast changes have been made owing to the advance of electricity. Modern ideas of time and space are quite different from those of our parents sixty years ago, or our grandparents ninety years ago. In our expresses we cover in an hour a stretch of country that the mail-coach took five times and the foot-passenger ten times as long to cover. As the experiments with the Berlin electric railway have lately shown, we can now travel two hundred kilometres in an hour. The journey from Europe to India now takes three weeks, whereas the earlier sailing-vessel took as many months. The immense saving of time that we make is equivalent to a lengthening of our own life. This applies also to the more rapid transit provided by balloons, automobiles, bicycles, etc. It is easy to estimate the value of these improvements; but it is only fully appreciated by those who have lived long in an uncivilized country without roads or among savages whose legs are their only means of locomotion.

This progress in the means of transit is not less valuable socially than personally. If we conceive the state as a unified organism of the higher order, the development of its means of transit corresponds in many ways to that of the circulation of the blood in the vertebrate frame. The easy, rapid, and convenient transport of the means of life from the centre to the most distant parts of the land, and the corresponding development of the net-work of railways and steamboat routes, are to a certain extent direct tests of the degree of civilization. To this we must add the creation of a large number of offices which provide steady employment and means of subsistence for many thousands.

To compare the complex sensations of civilized man with the much simpler ones of the savage we must consider first the functions of the outer organs of sense and then the internal sense-processes in the cortex of the brain. Fritz Schultze has pointed out in his _Psychology of the Savage_, in regard to both sets of organs, that the savage is a man of sense-life, the civilized human being a man of mind-life. When we remember that our higher psychic functions (sensation, will, presentation, and thought) are anatomically connected with the phronema (the thought-organ in the cortex), and the inner sense-perception with the central sensorium (in the sense-centres of the cortex), we shall expect to find the latter more developed in the savage and the former in civilized man. The external sense-action is more intense in quantity, but weaker in quality, in the savage than in civilized man; this is especially true of the finer and more complex sense-functions which we call æsthetic sensations and regard as the source of art and poetry. Most strongly developed of all in the savage is the power of perceiving distant objects (sight, hearing, smell), as they warn him of the dangers about him. It is just the reverse with the subjective and proximate feelings that are excited by the immediate touch of objects and are the special instruments of sensual enjoyment--taste, sex-sense, touch, and feeling of temperature. But in both kinds of sense-action the civilized man is far ahead of the savage in respect of the finer shades of feeling and æsthetic education. Moreover, modern civilization has provided man with various means of vastly increasing and improving the natural power of his senses. We need only mention the fields of knowledge that have been opened to us by the microscope and telescope, the refined chemical methods of modern cooking, etc. The finer æsthetic enjoyment which our advanced art affords--plastic art for the eye, music for the ear, perfumery for the nose, cuisine for the tongue--is generally unintelligible to the savage, although he can see much farther, and hear and smell much more acutely, than civilized man. And in the senses of near objects (taste, touch, temperature) the senses of the savages are more coarse, and incapable of the fine gradations of civilized man.

This more refined sense-life and the accompanying æsthetic enjoyment have no less social than personal value. We have, in the first place, the incalculable treasure of modern art and science, their promotion by the state, and their embodiment in the training of the young. In the future the higher races are likely to give more attention to this, training the senses of children as well as their intelligence from the earliest years, leading them to a closer observation of nature and reproduction of its forms by drawing and painting. The art-sense must also be fostered by the exhibition of models and by æsthetic exercises, a larger place must be given to artistic education along with the acquisition of real knowledge, and an appreciation of the beauties of nature must be created by means of walks and travels. Then the children of civilized races will have the inexhaustible sources of the finest and noblest pleasures in life opened to them in good time.

The higher psychic activity that civilized man calls his "mental life," and that is so often regarded as a kind of miracle, is merely a higher development of the psychic function we find at a lower level in the savage, and is shared by him with the higher vertebrates. Comparative psychology shows us, as I have explained in the seventh chapter of the _Riddle_, the long scale of development, which leads from the simple cell-soul of the protist up to the intelligence of man. I have already dealt in various chapters with this point, and need not enlarge on it any further to estimate the high personal value of mental life in every civilized human being. It is enough to remind the reader of the vast treasures of knowledge that lie open to every one of us at the commencement of the twentieth century--treasures of which our grandparents at the beginning of the last century had not the slightest presentiment.

Just as the individual has experienced a great advance in the value of his personal life by the higher culture of the nineteenth century, so the modern state itself has benefited by it in many ways. The many discoveries made in every branch of science and technical industry, the great advance in commerce and industrial life, in art and science, were bound to bring about a higher development of the whole mind of a modern community. Never, in the whole of history, has true science risen to such an astounding height as it has at the beginning of the twentieth century. Never before did the human mind penetrate so deeply into the darkest mysteries of nature, never did it rise so high to a sense of the unity of nature and make such practical use of its knowledge. These brilliant triumphs of modern civilization have, however, only been made possible by the various forces co-operating in a vast division of labor, and by the great nations utilizing their resources zealously for the attainment of the common end.

But we are still far from the attainment of the ideal. The social organization of our states is advanced only on one side; it is very reactionary on other sides. Unfortunately, the words of Wallace which I quoted in the _Riddle_ remain as true as ever. Our modern states will only pass beyond this condition in the course of the twentieth century if they adopt pure reason as their guide instead of faith and traditional authority, and if they come at length to understand aright "man's place in nature."

If we take a summary view of all that I have said on the increase in the value of human life by the progress of civilization, there can be no doubt that both the personal and the social value of life are now far higher than they were in the days of our savage ancestors. Modern life is infinitely rich in the high spiritual interests that attach to the possession of advanced art and science. We live in peace and comfort in orderly social and civic communities, which have every care of person and property. Our personal life is a hundred times finer, longer, and more valuable than that of the savage, because it is a hundred times richer in interests, experiences, and pleasures. It is true that within the limits of civilization the differences in the value of life are enormous. The greater the differentiation of conditions and classes in consequence of division of labor, the greater become the differences between the educated and uneducated sections of the community, and between their interests and needs, and, therefore, the value of their lives. This difference is naturally most conspicuous if we consider the leading minds and the greatest heights of the culture of the century, and compare these with the average man and the masses, which wander far below in the valley, treading their monotonous and weary way in a more or less stupid condition.

The state thinks quite otherwise than the individual man does of the personal worth of his life and that of his fellows. The modern state often demands for its protection the military service of all its citizens. In the eyes of our ministers of justice the value of life is the same whether there be question of an embryo of seven months or a new-born child (still without consciousness), an idiot or a genius. This difference between the personal and the social estimate of life runs through the whole of our moral principles. War is still believed by highly civilized nations to be an unavoidable evil, just as barbarians think of individual murder or blood-revenge; yet the murder of masses for which the modern state uses its greatest resources is in flagrant contradiction to the gentle doctrine of Christian charity which it employs its priests to preach every Sunday with all solemnity.

The chief task of the modern state is to bring about a natural harmony between the social and the personal estimate of human life. For this purpose we need, above all, a thorough reform of education, the administration of justice, and the social organization. Only then can we get rid of that mediæval barbarism of which Wallace speaks; to-day it finds expression triumphantly in our penal laws, our caste-privileges, the scholastic nature of our education, and the despotism of the Church.

For each individual organism the life of the individual is the first aim and the standard of value. On this rests the universal struggle for self-maintenance, which can be reduced in the inorganic world to the physical law of inertia. To this subjective estimate of life is opposed the objective, which proceeds on the value of the individual to the outer world. This objective value increases as the organism develops and presses into the general stream of life. The chief of these relations are those that come of the division of labor among individuals and their association in higher groups. This is equally true of the cell-states which we call tissues and persons, of the higher stocks of plants and animals, and of the herds and communities of the higher animals and men. The more these develop by progressive division of labor and the greater the mutual need of the differentiated individuals, so much the higher rises the objective value of the life of the latter for the whole, and so much the lower sinks the subjective value of the individual. Hence arises a constant struggle between the interests of individuals who follow their special life-aim and those of the state, for which they have no value except as parts of the whole.

XVIII

MORALITY

Dualistic ethics--The categorical imperative--Monistic ethics--Morals and adaptation--Variation and adaptation--Habit--Chemistry of habit--Trophic stimuli--Habit in inorganic bodies--Instincts--Social instincts--Instinct and morality--Right and duty--Morals and morality--The good and the bad--Morals and fashions--Sexual selection--Fashion and the feeling of shame--Fashion and reason--Ceremonies and cults--Mysteries and sacraments--Baptism--The Lord's Supper--Transubstantiation--The miracle of redemption--Papal sacraments--Marriage--Modern fashions--Honor--Phylogeny of morals.

The practical life of man is, like that of all the social higher animals, ruled by impulses and customs which we describe as "moral." The science of morality, ethics, is regarded by the dualists as a mental science, and closely connected with religion on the one hand and psychology on the other. During the nineteenth century this dualistic view retained its popularity especially because the great authority of Kant, with his dogma of the categorical imperative, seemed to have given it a solid foundation, and because it agreed admirably with the teaching of the Church. Monism, on the other hand, regards ethics as a natural science, and starts from the principle that morality is not supernatural in origin, but has been built up by adaptation of the social mammals to the conditions of existence, and thus may be traced eventually to physical laws. Hence modern biology sees no metaphysical miracle in morality, but the action of physiological functions.

Our whole modern civilization clings to the erroneous ideas which traditional morality, founded on revelation, and closely connected with ecclesiastical teaching, has imposed upon it. Christianity has taken over the ten commandments from Judaism, and blended them with a mystical Platonism into a towering structure of ethics. Kant especially lent support to it in recent years with his _Critique of Practical Reason_, and his three central dogmas. The close connection of these three dogmas with each other, and their positive influence on ethics, were particularly important through Kant formulating the further dogma of the categorical imperative.

The great authority which Kant's dualist philosophy obtained is largely owing to the fact that he subordinated pure reason to practical reason. The vague moral law for which Kant claimed absolute universality is expressed in his categorical imperative as follows: "So act that the maxim (or the subjective principle of your will) may at the same time serve as a general law." I have shown in the nineteenth chapter of the _Riddle_ that this categorical imperative is, like the thing in itself, an outcome of dogmatic, not critical, principles. As Schopenhauer says:

Kant's categorical imperative is generally quoted in our day under the more modest and convenient title of "the moral law." The daily writers of compendiums think they have founded the science of ethics when they appeal to this apparently innate "moral law," and then build on it that wordy and confused tissue of phrases with which they manage to make the simplest and clearest features of life unintelligible, without having ever seriously asked themselves whether there really is any such convenient code of morality written in our head, breast, or heart. This broad cushion is snatched from under morality when we prove that Kant's categorical imperative of the practical reason is _a wholly unjustified, baseless, and imaginative assumption_.

Kant's categorical imperative is a mere dogma, and, like his whole theory of practical reason, rests on dogmatic and not critical grounds. It is a fiction of faith, and directly opposed to the empirical principles of pure reason.

The notion of duty, which the categorical imperative represents as a vague _a priori_ law implanted in the human mind--a kind of moral instinct--can, as a matter of fact, be traced to a long series of phyletic modifications of the phronema of the cortex. Duty is a social sense that has been evolved _a posteriori_ as a result of the complicated relations of the egoism of individuals and the altruism of the community. The sense of duty, or conscience, is the amenability of the will to the feeling of obligation, which varies very considerably in individuals.

A scientific study of the moral law, on the basis of physiology, evolution, ethnography, and history, teaches us that its precepts rest on biological grounds, and have been developed in a natural way. The whole of our modern morality and social and juridical order have evolved in the course of the nineteenth century out of the earlier and lower conditions which we now generally regard as things of the past. The social morality of the eighteenth century proceeded, in its turn, from that of the seventeenth and sixteenth centuries, and still further from that of the Middle Ages, with its despotism, fanaticism, Inquisition, and witch trials. It is equally clear from modern ethnography and the comparative psychology of races that the morality of barbarous races has been evolved gradually from the lower social rules of savage tribes, and that these differ only in degree, not in kind, from the instincts of the apes and other social vertebrates. The comparative psychology of the vertebrates shows, further, that the social instincts of the mammals and birds have arisen from the lower stages of the reptiles and amphibia, and these in turn from those of the fishes and the lowest vertebrates. Finally, the phylogeny of the vertebrates proves that this highly developed stem has advanced through a long series of invertebrate ancestors (chordonia, vermalia, gastræada) from the protists by a process of gradual modification. We find, even among these unicellulars (first protophyta, then protozoa), the important principle which lies at the base of morality, association, or the formation of communities. The adaptation of the united cell-individuals to each other and to the common environment is the physiological foundation of the first traces of morality among the protists. All the unicellulars that abandon their isolated eremitic lives, and unite to form communities, are compelled to restrict their natural egoism, and make concessions to altruism in the common interest. Even in the globular cœnobia of volvox and magosphæra the special form and movement and mode of reproduction are determined by the compromise between the egoistic instincts of the individual cells and the altruistic need of the community.

Morality, whether we take it in the narrower or broader sense, can always be traced to the physiological function of adaptation, which is closely connected through nutrition with the self-maintenance of the organism. The change in the plasm which adaptation brings about is always based on the chemical energy of metabolism (chapter ix.). Hence it will be as well to have a clear idea of the nature of adaptation. I defined it as follows in my _General Morphology_:

Adaptation or variation is a general physiological function of organisms, closely connected with their radical function of nutrition. It expresses itself in the fact that every organism may be modified by the influence of the environment, and may acquire characters which were wanting in its ancestors. The causes of this variability are chiefly found in a material correlation between parts of the organism and the outer world. Variability or adaptability is not, therefore, a special organic function, but depends on the material, physico-chemical process of nutrition.

I have developed this conception of adaptation in the tenth chapter of the _History of Creation_.

The nature of the adaptation and its relation to variation are often conceived in different ways from that I have defined. Quite recently Ludwig Plate has restricted the idea, and understood by adaptation only variations that are _useful_ to the organism. He severely criticises my broader definition, and calls it "a palpable error," suggesting that I only retain it because I am not open to conviction. If I wanted to return this grave charge, I might point to Plate's one-sided and perverse treatment of my biogenetic law. Instead of doing this I will only observe that I think the restriction of adaptation to useful variations is untenable and misleading. There are in the life of man and of other organisms thousands of habits and instincts that are not useful, but either indifferent or injurious to the organism, yet certainly come under the head of adaptation, are maintained by heredity, and modify the form. We find adaptations of all sorts--partly useful, partly indifferent, partly injurious (the result of education, training, distortion, etc.)--in the life of man, and the domestic animals and plants. I need only refer to the influence of fashion and the school. Even the origin of the useless (and often injurious) rudimentary organs depends on adaptation.

Habit is a second nature, says an old proverb. This is a profound truth, the full appreciation of which came to us through Lamarck's theory of descent. The formation of a habit consists in the frequent repetition of one physiological act, and so is in principle reducible to cumulative or functional adaptation. Through this frequent repetition of one and the same act, which is closely connected with the memory of the plasm, a permanent modification is caused, either in a positive or a negative sense; _positively_ the organ is developed and strengthened by exercise, _negatively_ it is atrophied or enfeebled by disuse. When this accumulation of slight changes continues, the effect of adaptation goes so far in time as to produce new organs by progressive modification, or to cause actual organs to become useless and rudimentary, and finally disappear, owing to regressive metamorphosis.

When we make a careful study of the simpler processes of habit in the lower organisms, we see that they depend, like all other adaptations, on chemical changes in the plasm, and that these are provoked by trophic stimuli--that is to say, by external action on the metabolism. As Ostwald rightly says: "The most important function of organisms is the conversion of the various chemical energies into each other. The chemical energy that is taken into the organism as food is not generally capable of being applied directly to its purposes, but needs some further preparation. Every cell is a chemical laboratory, in which the most varied reactions take place without fires and retorts. The most frequently employed means in this is probably the catalytic acceleration of the usable and the catalytic retardation of the useless reactions. As a proof of this we have the regular presence of these enzyma in all organisms." In this the greatest importance attaches to memory, which I regard with Hering as a general property of living substance, "in virtue of which certain processes in the living being leave effects behind them that facilitate the repetition of the processes." I agree with Ostwald that "the importance of this property cannot be exaggerated. In its more general forms it effects adaptation and heredity, in its highest development the conscious memory." While the latter, and consciousness in general, reach the highest stage in the mental life of civilized man, the adaptation of the monera remains at the lowest stage. Among the latter the bacteria especially, which have assumed the most varied and important relations to other organisms in spite of the simplicity of their structure, show that this manifold adaptation depends on the formation of habits in the plasm, and is solely based on their chemical energy, or their invisible molecular structure. Once more the monera form a connecting link between the organic and inorganic; they fill up the deep gulf, from the point of view of energy, that seems to yawn between "animated" organisms and "lifeless" bodies.

According to the prevailing view, habit is a purely biological process, but there are processes even in inorganic nature which come under this head in the broader sense. Ostwald gives the following illustration:

If we take two equal tubes of thin nitric acid and dissolve a little metallic copper in one of them, the liquid will acquire the power to dissolve a second piece of the same metal more quickly than the one that remains unchanged. The cause of this phenomenon--which may be observed in the same way with mercury or silver and nitric acid--is that the lower oxydes of nitrogen that are formed in dissolving the metal accelerate the action of the nitric acid catalytically on the fresh metal. The same effect is produced if you put part of these oxydes in the acid; it then acts much more rapidly than pure acid. The formation of a habit consists, therefore, in the production of a catalytic acceleration during the reaction.

We may not only compare inorganic habit with organic adaptation, which we call habit or practice, but also with "imitation," which implies a catalytic transfer of habits to socially united living beings.

By instincts were formerly understood, as a rule, the unconscious impulses of animals which led to purposive actions, and it was believed that every species of animal had special instincts implanted in it by the Creator. Animals were thought, according to Descartes's view, to be unconscious machines whose actions proceed with unvarying constancy in the particular form that God had ordained. Although this antiquated theory of instinct is still taught by many dualistic metaphysicians and theologians, it has long since been demolished by the monistic theory of evolution. Lamarck had observed that most instincts are formed by habit and adaptation, and then transmitted by heredity. Darwin and Romanes especially showed afterwards that these inherited habits are subject to the same laws of variation as other physiological functions. However, Weismann has recently taken great pains in his _Lectures on the Theory of Descent_ (xxiii.) to refute this idea, and in general the hypothesis of an inheritance of acquired characters, because it will not harmonize with his theory of the germ-plasm. Ernst Heinrich Ziegler, who has recently (1904) published a subtle analysis of former and present ideas of instinct, agrees with Weismann that "all instincts are due to selection, and that they have their roots not in the practice of the individual life, but in the variations of the germ." But where else can we find the cause of these "germ-variations" except in the laws of direct and indirect adaptation? In my opinion, it is just the reverse; the remarkable phenomena of instinct yield a mass of evidence of progressive heredity, completely in the sense of Lamarck and Darwin.

The great majority of organisms live social lives, and so are united by the link of common interests. Of all the relations which determine the existence of the species, the chief are those which bind the individual to other individuals of the species. This is at once clear from the laws of sexual propagation. Moreover, the association of individuals is a great advantage in the struggle for existence. In the case of the higher animals this association becomes particularly important, because it is accompanied by an extensive division of labor. Then arises the antithesis of the personal egoism and the communal altruism; and in human societies the opposition of the two instincts is all the greater when reason recognizes that each has a right to satisfaction. Social habits become moral habits, and their laws are afterwards taught as sacred duties, and form the basis of the juridical order.

The morals of nations, so rich in psychological and sociological interest, are nothing more than social instincts, acquired by adaptation, and passed on from generation to generation by heredity. An attempt has been made to distinguish between the two kinds of habit by describing the instincts of animals as constant vital functions based on their physical organization, and the habits or morals of human beings as mental powers maintained by a spiritual tradition. This distinction has, however, been excluded by the modern physiological teaching that men's morals are, like all their other psychic functions, based physiologically on the organization of their brain. The habits of the individual man, which have been formed by adaptation to his personal conditions, become hereditary in his family; and these family usages can no more be sharply distinguished from the general morals of the community than these can be from the precepts of the Church and the laws of the state.

When a certain habit is regarded by all the members of a community as important, its cultivation favored and its breach punished, it is raised to the position of a duty. This is true even in the case of the herds of mammals (apes, gregarious carnivora, and ungulates) and the flocks of social birds (hens, geese, ducks). The laws which have been formed in these cases by the higher development of social instincts are particularly striking and equivalent to those of savage tribes when conspicuous individuals (old or strong males) have acquired a leadership of the troop, and successfully insure the observance of the proper habits or duties. Many of these organized bands are in some respects higher than the savages at the lowest stages who live in isolated families, or only form loose temporary associations of a few families. The great progress made by comparative psychology and ethnology, and historical and prehistorical research, in the second half of the nineteenth century, confirms us in the conviction that a long scale of intermediate stages joins the rudiments of law in the social primates and other mammals to the sense of law in the lower savage, and this again to that of the barbarian and the civilized human being--right up to the science of law in modern Europe.

Like civil laws, the commands of religion come originally from the morals of the savage, and eventually from the social instincts of the primates. The important province of mental life to which we give the vague name of religion was developed at an early stage among the prehistoric races from whom we all descend. When we study its origin from the point of view of empirical psychology and monistic evolution, we find that religion has arisen polyphyletically from different sources--ancestor worship, the desire of personal immortality, the craving for a causal explanation of phenomena, superstition of various kinds, the strengthening of the moral law by the authority of a divine law-giver, etc. According as the imagination of the savage or the barbarian followed one or other of these lines it raised up hundreds of religious forms. Only a few of them survived in the struggle for existence, and acquired (at least outwardly) dominion over the modern mind. But as independent and impartial science advances in our time, religion is purified of superstition and turns more and more to morality.

The obedience to the "divine commands" which religion demands of its followers is often transferred by human society to rules that have arisen from social customs of subordinate kinds. Thus we get the familiar confusion of manners and morals, of conventional outer deportment and real inner morality. The ideas of good and bad, morality and immorality, are subjected to arbitrary definitions. In this a great part is played by the moral pressure which is exercised by conventional ideas in the social body on the conduct and minds of its members. However clearly and rationally the individual thinks about the important questions of practical life, he has to yield to the tyranny of traditional and often quite irrational customs. As a matter of fact, both in life and in the nature of the case practical reason does take that precedence of pure reason which Kant claimed.

The tyranny of custom in practical life does not depend merely on the authority of social usage, but also on the power of selection. Just as natural selection insures the relative constancy of the specific form in the origin of the animal and plant species, so it has a powerful effect on the origin of morals and customs. An important factor in this is mimetic adaptation, or mimicry, the aping or imitating of certain forms or fashions by various classes of animals. This is unconscious in the case of many orders of insects, butterflies, beetles, hymenoptera, etc. When insects of a certain family come to resemble in their outer form and color and design those of another family, they obtain the protection or other advantages which these particular characters give in the struggle for life. Darwin, Wallace, Weismann, Fritz Müller, Bates, and others, have shown in numbers of instances how the origin of these deceptive resemblances can be traced to natural selection, and how important they are in the formation of the species. But many customs and usages in human life arise in just the same way, partly by conscious and partly by unconscious imitation. Of these the varying external forms which we call "fashions" have a most important influence in practical life. The phrase "fashion-ape," when used in a scientific sense, is not merely an expression of contempt, but has also a profound meaning; it correctly indicates the origin of fashions by imitation, and also the peculiar resemblance we find in this respect between man and his cousins, the apes. Sexual selection among the primates has a good deal to do with this.

The great importance which Darwin ascribes in his _Descent of Man_ to the æsthetic selection of the respective sexes is equally true of man and of all the higher vertebrates that have a feeling of beauty, especially the amniotes (mammals, birds, and reptiles). The beautiful coloring and marking and ornamentation which distinguish the males from the females are due entirely to the careful individual selection of the former by the latter. Thus the various kinds of ornamental hair (beard, hair of head, etc.), the tint of the face, the peculiar form of the lips, nose, ears, etc., are to be explained, as we find them in man and the male ape; also the brilliant plumage of the humming-bird, the bird of paradise, pheasant, etc. I have dealt fully with these interesting facts in the eleventh chapter of the _History of Creation_, and must refer the reader thereto. I will only point out here how valuable the whole of this chapter of Darwinism is for the understanding of the foundation of species on the one hand and men's fashions and customs on the other. It is most closely connected with ethical problems.

The growth of fashion in civilized life is very important, not only for the development of the sense of beauty and for the sexual selection of the sexes, but also in connection with the origin of the feeling of shame and the finer psychological traits that relate to it. The lower savages have no more sense of shame than animals or children. They are quite naked, and accomplish the sexual act without the slightest trace of shame. The beginning of clothing which we find among the middle savages is not due to a sense of shame, but partly to low temperature (in the polar regions), partly to vanity and love of decoration (such as ornamenting the ears, lips, nose, and sex-organs by the insertion of shells, pieces of wood, flowers, stones, etc.). Afterwards the sense of shame sets in, and we have the covering of certain parts of the body with leaves, girdles, shirts, etc. In most nations the sexual parts are the first to be covered; though some attach importance to the veiling of the face. In many Oriental tribes (especially Mohammedan) it is still the first precept of female chastity to veil the face (the most characteristic part of the individual), while the rest of the body may remain naked. Generally speaking, the æsthetic and psychological relations of the sexes play the chief part in the higher development of morals. Morality is often taken to be synonymous with the law of sexual intercourse.

As the features of civilized life advance, the influence of reason increases, and so does the power of hereditary tradition and the moral ideas associated with it. The result is a severe conflict between the two. Reason seeks to judge everything by its own standard, to learn the causes of phenomena and direct practical life accordingly. On the other hand tradition, or "good morals," looks at everything from the point of view of our forefathers and other venerable laws and religious precepts. It is indifferent to the independent discoveries of reason and the real causes of things. It demands that the practical life of every individual be framed in accordance with the hereditary morality of the race or state. Thus we get the inevitable conflict between reason and tradition, or science and religion, which continues in our own day. Sometimes in the course of it a "new fashion" is substituted for some sacred tradition, a transitory custom that succeeds in imposing itself by its novelty or curiosity; and when this has contrived to win general acceptance, or has gained the support of Church or state to some extent, it is regarded in much the same light as the older morality.

The lowest races of the present time (for instance, the pithecoid pygmies, the Veddahs of Ceylon, the Akkas of Central Africa) are very little higher than their primate ancestors in mental development. This is also true of their habits of life and morals. As their ideas are for the most part concrete and sensual, their power of forming abstract concepts is very little developed; they have hardly any religious ideas to speak of. But with the middle savages we begin to find the craving to know the causes of things and the idea of spirits that are concealed behind the phenomena of sense. Dread of these leads to worship, fetichism, and animism, the beginning of religion. Even at this early stage of worship we find certain customs associated with the cult to which a symbolical or mysterious meaning is given. These ceremonies lead on in the higher races to the great religious festivities, which the Greeks called "mysteries." Sensual images of various kinds are mixed up in them with supersensual ideas and superstitions. The festivals, processions, dances, hymns, and sacrifices of all sorts that form part of the cult are more or less concerned with the mysterious, and are therefore considered "holy." They are often made the pretext of sensual gratifications, which end in gross immorality and orgies.

From the older pagan and Jewish religious usages were afterwards developed in the Christian Church those parts of the cult which are known as sacraments. These miraculous sacraments, by the mysterious action of which man is supposed to be born again or regenerated, very quickly became powerful instruments in the hand of the Church and thorny problems for theologians, especially after Gregory the Great introduced the dogmas of Purgatory and the relieving power of the Mass. According to St. Thomas of Aquin, the sacraments are channels that convey the grace of God to sinful man. The papal authorities fixed their number at seven (baptism, eucharist, penance, confirmation, matrimony, orders, and extreme unction) in the twelfth century. The superstitious content of these sacraments was generally lost sight of in the glamour of their ceremonious side, but their authority was unshaken. Since the Reformation the Protestants have retained only the two chief sacraments which were founded by Christ himself--Baptism and the Lord's Supper.

Christian baptism is a continuation of the older ceremonies of washing and purification that were in use thousands of years before Christ among nations of the East and among the Greeks. They combined the hygienic value of the bath with the idea of a regeneration of the soul and spiritual purification. Augustine, who founded the dogma of original sin, held that the baptism of children was necessary for the salvation of their souls, and it then became general. It has since given rise to a number of superstitious ideas and unfortunate family troubles, but it is still regarded as a sacred ceremony. Millions of Christians still believe that the child's soul is saved (though it has no consciousness whatever when baptized) and delivered from the power of the devil and the curse of sin by baptism.

The second sacrament that Luther retained is the Lord's Supper, or the sacrament of the body and blood of Christ. It was instituted by Christ on the night before his death, and is a continuation of the paschal supper of the Jews, in which the head of the house shared bread and wine with his family with certain ritual ceremonies. In this paschal supper the people of Israel celebrated their release from the bondage of Egypt and their distinction as the "chosen people." By connecting his "last supper" with the traditional rite of the Jews, Christ sought on the one hand to found the new dispensation on the old, and on the other hand to institute a love-feast (communion or agape) among his followers. Like baptism, the Lord's Supper led afterwards to the bitterest controversy among theologians.

The differences of opinion as to the Eucharist in the Middle Ages culminated at last in the opposition of the two reformers, Luther and Zwingli. The latter, the founder of the Free Reformed Church, saw in the Supper only a symbolical act and a commemoration of Christ. Luther, however, adhered to the mysterious miracle that had been defined in 1215 by the dogma of transubstantiation. Bread and wine are believed on this view to be converted physically into the body and blood of Christ! I was taught this in 1848 by the minister who prepared me for confirmation, and to whom I was greatly attached. We were actually to perceive this change when we assisted at the Supper for the first time, if we did so with real faith. As I was quite conscious of having this quality, I had great expectations of the miracle. But I was very painfully disillusioned when I found only the familiar taste of bread and wine, not the flesh and blood that faith had desired. I had to regard myself (then a boy of fourteen years) as an utterly abandoned sinner, and it was with the greatest difficulty that my parents succeeded in pacifying me over my want of faith.

I have spoken somewhat fully in the seventeenth chapter of the _Riddle_ of the view of the papacy and ultramontanism which modern historical and anthropological science leads us to form. No one who has any idea of history and of the metamorphoses of religion can question that Romanism is a miserable caricature of primitive Christianity; it retains the name, but has completely reversed the principles. In the course of its domination, from the fourth to the sixteenth century, the papacy has raised up the marvellous structure of the Catholic hierarchy, but has departed farther and farther from the stand-point of pure Christianity. The aim of Romanism is to-day, as it was a thousand years ago, to dominate and exploit a blindly believing humanity. It finds admirable instruments for this in its mystic sacraments, to which it has ascribed an "indelible character." From the cradle to the grave, from baptism to the last anointing, in confirmation and penance, the believer must be reminded that he must live as an obedient and self-sacrificing child; and the sacrament of ordination must teach him that the priest, with his higher inspiration, is the only intermediary between man and God. The symbolical rites that are associated with these sacraments serve to surround them with the magic of the mysterious and exclude the penetration of reason. This is particularly true of the sacrament that has had the greatest practical influence--matrimony.

In view of the extreme importance of the life of the family as a foundation of social and civic life, it is advisable to consider marriage from the biological point of view, as an orderly method of reproduction. Here, as in all other sociological and psychological questions, we must be careful not to accept the present features of civilized life as a general standard of judgment. We have to take a comparative view of its various stages, as we find them among barbarians and savages. When we do this impartially, we see at once that reproduction, as a purely physiological process having for its end the maintenance of the species, takes place in just the same way among uncultivated races as among the anthropoid apes. We may even say that many of the higher animals, especially monogamous mammals and birds, have reached a higher stage than the lower savages; the tender relations of the two sexes towards each other, their common care of their young, and their family life, have led to the development of higher sexual and domestic instincts, to which we may fitly ascribe a moral character. Wilhelm Bölsche has shown, in his _Life of Love in Nature_, how a long series of remarkable customs has been developed in the animal world by adaptation to various forms of reproduction. Westermarck has pointed out, in his _History of Marriage_, how the crude animal forms of marriage current among savages have been gradually elevated as we rise to higher races. As the sensual pleasure of generation is combined with the finer psychological feeling of sympathy and psychic attachment, the latter gains constantly on the former, and this refined love becomes one of the richest sources of the higher spiritual functions, especially in art and poetry. Marriage itself, of course, remains a physiological act, a wonder of life, with the organic sex impulse as its chief foundation. As the conclusion of marriage represents one of the most important moments in human life, we find it accompanied by symbolic ceremonies and festive rites even among lower tribes. The immense variety of marriage festivals shows how this important act has appealed to the imagination. Priests quickly recognized this, and decked out marriage with all kinds of ceremonies and turned it to the advantage of their Church. While the Catholic Church raised it to the status of a sacrament and ascribed to it an "indelible" character, it declared that it was indissoluble when performed according to ecclesiastical rite. This unwholesome influence of Romanism, this dependence of matrimony on religious mysteries and ceremonies, and difficulty of obtaining divorce, etc., still continue in our day. It is only a short time since the German Reichstag, under the influence of the Centre [Catholic] party, added laws to its civic code which increase instead of lessening the difficulty of obtaining divorce. Reason demands the liberation of marriage from ecclesiastical pressure. It demands that matrimony be grounded on mutual love, esteem, and devotion, and that it at the same time be counted a social contract, and be protected, as civil marriage, by proper legislation. But when the contracting parties find (as so often happens) that they have mistaken each other's character, and that they do not suit each other, they should be free to dissolve the bond. The pressure which comes of marriage being regarded as a sacrament, and which prevents the dissolution of unhappy marriages, is merely a source of vice and crime.

We find in many other features of our social life, besides marriage, a contradiction between the demands of reason and the traditional usages which modern civilization has taken over as a heritage from earlier and lower nations, and partly from barbarians and savages. In the public life of states this contradiction is much more striking than in the private life of the family or the individual. Whereas the milder teaching of the Christian religion--sympathy, love of one's fellows, patience, and devotion--has had a good influence in many ways, there can be no question of this in the international relations of the nations; here we find pure egoism. Every nation seeks to take advantage of others by cunning or force, and, wherever possible, to subjugate them: if they will not consent, the brute force of war is employed. Social misery of all kinds spreads wider and wider, almost in proportion as civilization develops. Alexander Sutherland is right when he characterizes "the leading nations of Europe and their offshoots" (in the United States) as _lower_ civilized races. In some respects we are still barbarians.

How far the bulk of modern nations still are from the ideal and the reign of pure reason can be seen by a glance at the social, juridical, and ecclesiastical condition of "these leading nations of Europe," either Teutonic or Latin. We need only consider with an unprejudiced mind the accounts in our journals of parliamentary and legal proceedings, government measures and social relations, in order to realize that the force of tradition and fashion is immense, and resists the claims of reason on every side. This is most clearly seen externally in the power of fashion, especially as regards clothing. There is a good ground for the complaint about "the tyranny of fashion." However unpractical, ridiculous, ugly, and costly a new garment may be, it becomes popular if it is patronized by authority, or some clever manufacturer succeeds in imposing it by specious advertisements. We need only recall the crinoline of fifty years ago, the bustle of twenty years ago, and the exposure of the breast and back by low dresses (with the object of sexual excitement) which was the fashion of forty years ago.[11] For centuries we have had the pernicious fashion of the corset, an article that is as offensive from the æsthetic as from the hygienic point of view. Thousands of women are sacrificed every year to this pitiful fashion, through disease of the liver or lungs; nevertheless, the craze for the hour-glass shape of the female form continues, and the reform of clothing makes little headway. It is just the same with numbers of fashions in the home and in society, of devices in commerce and laws in the state. Everywhere the demands of reason advance little in their struggle with the venerable usages of tradition.

A false sense of honor dominates our social life, just as a false sense of modesty controls our clothing. The true honor of man or woman consists in their inner moral dignity, in the determination to do only what they conceive to be good and right, not in the outer esteem of their fellows or in the worthless praise of a conventional society. Unfortunately, we have to admit that in this respect we are still largely ruled by the foolish views of a lower civilization, if not of crude barbarians.

In many other features of our life besides this false modesty and false honor we perceive the force of social usage. Many of what are thought to be honorable customs are relics of barbarism; much of our morality is, in the light of pure reason, downright immorality. As even the latter is due to adaptation, and as the same custom may be at one time thought useful and fitting, at another time injurious and bad, we see again that it is impossible to restrict the idea of adaptation to useful variations. We may say the same of the changing rules of education, commerce, legislation, and so on. The ideal in all departments of life is pure reason; but it has to struggle long against the current prejudices and customs, which find their chief support in the superstitions of the Church and the conservative tendencies of the state. In this state of Byzantine immorality, decorating itself so often with the mantle of piety, practical materialism flourishes, while monism, or theoretical materialism, is thrust aside.

If we sum up all that monistic science has taught us as to the origin and development of morality, we may put it in the following series of propositions: 1. By adaptation to different conditions of life the simple plasm of the earliest organisms, the archigonous monera, undergoes certain modifications. 2. As the living plasm reacts on these influences, and the reaction is often repeated, a habit is formed (as in the catalysis of certain inorganic chemical processes). 3. This habit is hereditary, the repeated impressions being fixed in the nucleus (or caryoplasm) in the case of the unicellulars. 4. When hereditary transmission lasts through many generations, and is strengthened by cumulative adaptation, it becomes an instinct. 5. Even in the protist cœnobia (the cell-communities of the protophyta and protozoa) social instincts are formed by association of cells. 6. The antithesis of the individual and social instinct, or of egoism and altruism, increases in the animal kingdom in proportion to the development of psychic activity and social life. 7. In the higher social animals definite customs arise in this way, and these become rights and duties when obedience to them is demanded by the society (herd, flock, people) and the breach of them punished. 8. Savage races at the lowest stage, without religion, are not differently related to their customs than the higher social animals. 9. The higher savages develop religious ideas, combine their superstitious practices (fetichism and animism) with ethical principles, and transform their empirical moral laws into religious commands. 10. Among barbaric, and more particularly among civilized, races definite moral laws are formed by the association of these hereditary religious, moral, and legal ideas. 11. In the civilized races the Church formulates the religious commands, and jurisprudence the legal commands, in more definitely binding forms; the advancing mind remains, however, subject in many respects to Church and state. 12. In the higher civilized nations pure reason gains more and more influence on practical life, and thrusts back the authority of tradition; on the basis of biological knowledge a rational or monistic ethic is developed.

XIX

DUALISM

Dualistic systems of Kant I. and Kant II.--His antinomies--Cosmological dualism--The two worlds--The world of bodies and the world of spirits--Truth and fiction--Goethe and Schiller--Realism and idealism--Anti-Kant--Law of substance--Attributes of substance--Sensation and energy--Passive and active energy--Trinity of substance: matter, force, and sensation--Constancy of sensation--Psyche and physics--Reconciliation of principles.

The history of philosophy shows how the mind of man has pressed along many paths during the last two thousand years in pursuit of truth. But, however varied are the systems in which its efforts have found embodiment, we may, from a general point of view, arrange them all in two conflicting series--monism, or the philosophy of unity; and dualism, or the philosophy of the duality of existence. Lucretius and Spinoza are distinguished and typical representatives of monism; Plato and Descartes the great leaders of dualism. But besides the consistent thinkers of each school there are a number of philosophers who vacillate between the two, or who have held both views at different periods of life. Such contradictions represent a personal dualism on the part of the individual thinker. Immanuel Kant is one of the most famous instances of this class; and as his critical philosophy has had a profound influence, and I was compelled to contrast my chief conclusions with those of Kant, I must once more deal briefly with his ideas. This is the more necessary as one of the ablest of the many attacks on the _Riddle_, the _Kant against Haeckel_ of Erich Adick, of Kiel, belongs to this school.

In the _Creed of Pure Reason_, which I published as an appendix to the popular edition of the _Riddle_ in 1903, I pointed out, in view of this and similar Kantist criticisms, the clear inconsistency of the great evolutionary principles of Kant, the natural philosopher, with the mystic teaching which he afterwards made the foundation of his theory of knowledge, and that is still greatly esteemed. Kant I. explained the constitution and the mechanical origin of the universe on Newtonian principles, and declared that mechanicism alone afforded a real explanation of phenomena; Kant II. subordinated the mechanical principle to the teleological, explaining everything as a natural design. Kant I. convincingly proved that the three central dogmas of metaphysics--God, freedom, and immortality--are inacceptable to pure reason. Kant II. claimed that they are necessary postulates of practical reason. This profound opposition of principles runs through Kant's whole philosophic work from beginning to end, and has never been reconciled. I had already shown in the _History of Creation_ that this inconsistency has a good deal to do with Kant's position in regard to evolution. However, this radical contradiction of Kant's views has been recognized by all impartial critics. It has lately been urged with great force by Paul Rée in his _Philosophy_ (1903). We need not, therefore, linger in proving the fact, but may go on to consider the causes of it.

A subtle and comprehensive thinker like Kant was naturally perfectly conscious of the existence of this inconsistency of his dualistic principles. He endeavored to meet it by his theory of antinomies, declaring that pure reason is bound to land in contradictions when it attempts to conceive the whole scheme of things as a connected totality. In every attempt to form a unified and complete view of things we encounter these unsolvable antinomies, or mutually contradictory theses, for both of which sound proof is available. Thus, for instance, physics and chemistry say that matter must consist of atoms as its simplest particles; but logic declares that matter is divisible _in infinitum_. On the one theory time and space are infinite; on the other theory, finite. Kant attempted to reconcile these contradictions by his transcendental idealism, by the assumption that objects and their connection exist only in our imagination, and not in themselves. In this way he came to frame the false theory of knowledge which is honored with the title of "criticism," while as a matter of fact it is only a new form of dogmatism. The antinomies are not explained by it, but thrust aside; nor was there more truth in the assertion that equal proof is available for theses and antitheses.

The famous work of Kant's earlier years, _The General Natural History and Theory of the Heavens_ (1755), was purely monistic in its chief features. It embodied a fine attempt "to explain the constitution and mechanical origin of the universe on Newtonian principles." It was mathematically established forty years afterwards by Laplace in his _Exposition du système du monde_ (1796). This fearless monistic thinker was a consistent atheist, and told Napoleon I. that there was no room for "God" in his _Mécanique celeste_ (1799). Kant, however, afterwards found that, though there was no rational evidence of the existence of God, we must admit it on moral grounds. He said the same of the immortality of the soul and the freedom of the will. He then constructed a special "intelligible world" to receive these three objects of faith; he declared that the moral sense compelled us to believe in a supersensual world, although pure theoretical reason is quite unable to form any distinct idea of it. The categorical imperative was supposed to determine our moral sense and the distinction between good and evil. In the further progress of his ethical metaphysics Kant expressly urged that practical reason should take precedence of theoretical--in other words, that faith is superior to knowledge. In this way he enabled theology and irrational faith to find a place in his system and claim supremacy over all rational knowledge of nature.

The older Greek philosophy had been purely monistic, Anaximander and his disciple Anaximenes (in the sixth century B.C.) conceiving the world in the sense of our modern hylozoism, but Plato introduced (two hundred years afterwards) the dualistic view of things. The world of bodies is real, accessible to our sensible experience, changeable and transitory; opposed to it is the world of spirits, only to be reached by thought, supersensual, ideal, immutable, and eternal. Material things, the objects of physics, are only transient symbols of the eternal ideas, which are the subject of metaphysics. Man, the most perfect of all things, belongs to both worlds; his material frame is mortal, the prison of the immortal and invisible soul. The eternal ideas are only embodied for a time in the world of bodies here below; they dwell eternally in the world of spirits beyond, where the supreme idea (God, or the idea of the good) controls all in perfect unity. The human soul, endowed with free-will, is bound to develop the three cardinal virtues (wisdom, fortitude, and prudence) by the cultivation of its three chief moral faculties (thought, courage, and zeal). These fundamental principles of Plato's teaching, systematically presented by his pupil Aristotle, met with a very general acceptance, as they could easily be combined with the teaching of Christianity which arose four hundred years afterwards. The great majority of later philosophic and religious systems followed the same dualistic paths. Even Kant's metaphysics is only a new form of it; only its dogmatic character is hidden by the ascription to it of the convenient title of the "critical" system.

Modern science has opened out to us immense departments of the real world that are accessible to observation and rational inquiry; but it has not taught us a single fact that points to the existence of an immaterial world. On the contrary, it has shown more and more clearly that the supposed world beyond is a pure fiction, and only merits to be treated as a subject for poetry. Physics and chemistry in particular have proved that all phenomena that come under our observation depend on physical and chemical laws, and that all can be traced to the comprehensive and unified law of substance. Anthropogeny has taught us the evolution of man from animal ancestors. Comparative anatomy and physiology have shown that his mind is a function of the brain, and his will not free; and that his soul, absolutely bound up with its material organ, passes away at death like the souls of other mammals. Finally, modern cosmology and cosmogony have found no trace whatever of the existence and activity of a personal and extramundane God. All that comes within the range of our knowledge is a part of the material world.

In his observations on the supersensual world Kant lays stress on the fact that it lies beyond the range of experience, and is known only by faith. Conscience, he thinks, assures us of its existence, but does not give us any idea of its nature; and so the three central mysteries of metaphysics are mere words without meaning. But, as nothing can be done with mere words, Kant's followers have attempted to put a positive substance into them, generally in relation to traditional ideas and religious dogmas. Not only orthodox Kantians, but even critical philosophers like Schleiden, have dogmatically asserted that Kant and his disciples have established the transcendental ideas of God, freedom, and immortality, just as Kepler, Newton, and Laplace established the laws of celestial motion. Schleiden imagined that this dogmatic affirmation would refute "the materialism of modern German science." Lange has shown, on the contrary, that such dogmatism is utterly foreign to the spirit of the _Critique of Pure Reason_, and that Kant held the three ideas to be quite incapable of either positive or negative proof, and so thrust them into the domain of practical philosophy. Lange says: "Kant would not see, as Plato would not see before him, that the intelligible world is a world of poetry, and has no value except in this respect." But if these ideas are mere figments of the poetic imagination, if we can form neither positive nor negative idea of them, we may well ask: What has this imaginary spirit-world to do with the pursuit of truth?

As I have raised the question of the limits of truth and fiction, I may take the opportunity of pointing out the general importance of this distinction. Undoubtedly man's knowledge is limited, from the very nature of our faculties or the organization of our brain and sense-organs. Hence, Kant is right when he says that we perceive only the phenomena of things, and not their inner essence, which he calls the "thing in itself." But he is wrong and altogether misleading when he goes on to doubt the reality of the external world, and says it exists only in our presentations--in other words, that life is a dream. It does not follow, from the fact that our senses and phronema can reach only a part of the properties of things, that we call into question their existence in time and space. But our rational craving for a knowledge of causes impels us to fill up the gaps in our empirical knowledge by our imagination, and thus form an approximate idea of the whole. This work of the imagination may be called "fiction" in a broad sense--hypotheses when they are in science, faith when they belong to religion. However, these imaginative constructions must always take a concrete form. As a fact, the imagination that constructs the ideal world is never content merely to assume its existence, but always proceeds to form an image of it. But these forms of faith have no theoretical value for philosophy if they contradict scientific truth, or profess to be more than provisional hypotheses; otherwise they may be of practical service, but are theoretically useless. Hence we fully recognize the great ethical and pedagogical value of poetry and myths, but are by no means disposed to give them precedence of empirical knowledge in our quest of the truth. I agree entirely with the excellent criticism of Kant which Albert Lange gives in his _History of Materialism_ (vol. ii.); but I am unable to follow him when he transfers his idealism from practical to theoretical questions, and urges the erroneous theory of knowledge derived from it in opposition to monism and realism. It is true that, as Lange says:

Kant did not lack the sense for the conception of this intelligible world (as an imaginative world); but his whole education and the period in which his mental life developed prevented him from indulging it. As he was denied the liberty of giving a noble form, free from all mediæval distortion, to the vast structure of his ideas, his positive philosophy was never fully developed. His system, with its Janus face, stands at the limit of two ages. He himself, in spite of all the defects of his deductions, is a teacher of the ideal. Schiller especially has grasped with prophetic insight the very essence of his teaching, and purified it of its scholastic dross. Kant held that we must only think, not see, the intelligible world; though what he thinks must have objective reality. Schiller has rightly brought the intelligible world visibly before us by treating it as a poet, and thus following in the footsteps of Plato, who, in contradiction to his own dialectic, reached his highest thought when he allowed the supersensual to become a thing of sense in the myth. Schiller, the poet of freedom, dared to carry freedom openly into the land of dreams and of shadows; then there arose under his hand the dreams and shadows of the ideal.

In view of the great influence that Schiller's idealism has had in the spread of Kant's practical moral philosophy, we may for a moment consider it in contrast with the realistic views of Goethe.

The profound opposition of the views of the two greatest poets of the classical period of German literature is rooted deep in their natures. This has been proved so often and so thoroughly, and has so frequently been represented as the complementary quality of the two poets, that I need merely recall it here. As for Goethe, I have, in my _General Morphology_, shown his historical importance in connection with the theory of evolution and the system of monism. With all his versatile occupations, this great genius found time to devote to the morphological study of organisms, and to establish his comprehensive biological theories on this empirical basis. His discovery of the metamorphosis of plants and his vertebral theory of the skull justify us in classifying him as one of the chief forerunners of Darwin. When I dealt with this in the fourth chapter of the _History of Creation_, I pointed out how great an influence these morphological studies, together with his idea of evolution, had on the realism of his philosophy. They led him direct to monism and to an admiration of Spinoza's monistic pantheism. Schiller had neither great interest nor clear insight for these studies. His idealistic philosophy disposed him rather to Kant's dualistic metaphysics and to an acceptance of the three central mysteries--God, soul, and freedom. Both Schiller and Goethe had a thorough knowledge of anthropology and psychology. But the anatomic and physiological studies that Schiller made as a military surgeon had very little influence on his transcendental idealism, in which the ethical-æsthetic element preponderated. On the other hand, Goethe's empirical realism was profoundly influenced by his medical studies at Strasburg, and especially by his later comparative anatomical and botanical investigations at Jena and Weimar.

The philosophic antithesis which we thus find in the biological foundations of the views of Goethe and Schiller represents to an extent the Janus face that the philosophic genius of the German people bears to our own day. Goethe, the realist, penetrated deep into the empirical study of the material world, and sought, with Spinoza, to establish the unity of the universe. Schiller, the idealist, lives rather in the spirit-world, and seeks, with Kant, to utilize its ethical ideals--God, freedom, and immortality--for the education of the human race. Both tendencies of thought have led the genius of Germany--like the genius of Greece, two thousand years ago--to a great number of vast intellectual achievements. Goethe wrought the ideal in his practical life, Kant discovered it, Schiller proclaimed it to be the fittest aim of the future.

It is wrong to conclude from isolated quotations from Goethe that he occasionally betrayed the dualism of Schiller in his opinions. Some of the remarks in this connection that Eckermann has left us from his conversations with Goethe must be taken very carefully. Generally speaking, this source is not reliable; many of the observations that the mediocre Eckermann puts into the mouth of the great Goethe are quite inconsistent with his character, and are more or less perverted. Hence, when recent high-placed orators declare at Berlin that Goethe saved the high ideals of God, freedom, and immortality, like Schiller, and thus borrow a certain support for their Christian belief, they only show how little they have grasped the profound antithesis of the views of the two poets. Goethe notoriously described himself as a "renegade non-Christian." The creed of the "great heathen" Goethe, as we find it in _Faust_ and _Prometheus_ and _God and the World_, and a hundred other magnificent poems, is pure monism, of the pantheistic character which we take to be alone correct--hylozoism; he is equally far from the one-sided materialism of Holbach or Carl Vogt and the extreme dynamism of Leibnitz and Ostwald. Schiller by no means shared this realistic view of things; his idealistic sense fled beyond nature into the spirit world. However, our theoretic hylozoism does not exclude practical idealism, as Goethe's whole life showed. On the other hand, princes and priests often let us see how easily theoretical idealism goes with practical materialism, or hedonism.

In the month of February, 1904, the centenary of the death of Kant was celebrated throughout the world of culture. In numbers of academic speeches and writings he was greeted as the greatest thinker of Germany. He died on the same date (February 12th) on which Darwin was born five years later. It is unquestionable that Kant has had an immense influence on the whole development of German philosophy. But while recognizing his extraordinary genius, we must not be blind to the glaring contradictions and defects of his dualist system. From the monistic point of view, we can only regard his profound influence during the whole of the nineteenth century as mischievous. Most certainly he had a quite exceptional talent for philosophic speculation and penetrating thought, and he added to his great mental qualities a blameless character and an undeniable sense of truth in life (though not in thought). It was a serious misfortune for Kant and for the philosophic school he led that his education prevented him from acquiring a thorough knowledge and correct conception of the real world. Shut up throughout life within the narrow bounds of his native town, Königsberg, he never travelled beyond the frontier of Prussia, and so did not obtain that knowledge of the world that comes of travelling. In the study of nature he confined himself to the physics of the inorganic world, in the study of man to the immortal soul. At the close of his university studies Kant had to earn his living as a house-teacher for nine years (from twenty-two to thirty-one), just at the most important period of his life, in which the independent development of the personal and scientific character is decided when the academic studies are over.

In such adverse circumstances of mental adaptation a deep mystic trait, which had been inherited from pious parents and confirmed by the strictly religious training of his early years, was fixed in Kant's character. Hence it was that faith in the three central mysteries came upon him more and more in later years: he gave them precedence over all the attainments of theoretical reason, while granting that we can form neither a negative nor positive idea of them. But how can the belief in God, freedom, and immortality determine one's whole view of life as a postulate of practical reason if we cannot form any definite idea of them?

Every philosophy that deserves the name must have clear ideas as the bases of its thought-structure; it must have definite views in connection with its fundamental conceptions. Hence most of Kant's followers have not been content to follow his direction merely to _believe_ in the three central mysteries; they have sought to associate definite mental pictures with the empty concepts of God, freedom, and immortality. In this they have drawn upon the religious imagination, and have passed from the real knowledge of nature into the transcendental realm of poetry. Monism, based on this real knowledge of nature, has to keep clear of such dualism.

The extraordinary glorification of Kant that took place on the occasion of his centenary must have seemed strange to many scientists who recognize in his idealism one of the greatest hinderances to the spread of the modern monistic philosophy of nature. But it is not difficult to explain this. We must remember, in the first place, the contradictory views that are embodied in Kant's system; every one could find in Kant's works something to correspond to his own convictions--the monistic physicist could read of the mechanical sway of natural law throughout the whole knowable world, and the dualistic metaphysician of the free play of the divine aim in the spiritual world. The physician and physiologist would note with satisfaction that in his criticism of pure reason Kant had been unable to find any evidence for the existence of God, the immortality of the soul, or the freedom of the will. The jurist and theologian would find with equal gratification that in the practical reason Kant claims these three central dogmas as necessary postulates. I have shown to some extent, in the sixth chapter of the _Riddle_, how these irreconcilable contradictions in Kant's system are due to a psychological metamorphosis.

It is just these very contradictions, which run through Kant's philosophy from beginning to end, that maintain its popularity. Educated people who desire to form a view of life rarely read Kant's difficult (and often obscure) works in the original, but are content to learn from extracts, or from a history of philosophy, that the Königsberg thinker succeeded in squaring the circle, or in reconciling natural science with the three central dogmas of metaphysics. The "higher powers," who are particularly concerned to save the latter, favor the teaching of Kant's dogmas, because it closes the way to real explanation and prevents independent thinking. This is especially true of the ministers of public instruction in the two chief German states--Prussia and Bavaria. In their open attempt to subordinate the school to the Church, they desire, above all, the primacy of practical reason--that is to say, the subjection of pure reason to faith and revelation. In German universities to-day belief in Kant is a sort of ticket of admission to the study of philosophy. The reader who would realize the pernicious effect of this official faith in Kant on the advance of scientific knowledge will do well to read the able criticism in the brilliant posthumous work of Paul Rée.

In the face of the dualism which still prevails in the academic teaching of philosophy (especially in Germany) we must base our monistic system on the universality of the law of substance. This harmoniously combines the laws of the conservation of matter and of energy. As I have fully explained my own conception of this law in the twelfth chapter of the _Riddle_, I will only say here that its validity is quite independent of any particular theory of the relations of matter and force.[12] The materialism of Holbach and Büchner lays a one-sided stress on the importance of matter: the dynamism of Leibnitz and Ostwald on that of force. If we avoid these extremes, and conceive matter and force as inseparable attributes of substance, we have pure monism, as we find it in the systems of Spinoza and Goethe. We might then substitute for the word "substance" as Hermann Cröll does, the term "force-matter." The further question as to the correctness of any particular physical conception of matter is quite independent of this.

The two knowable attributes or inalienable properties of substance, without which it is unthinkable, were described by Spinoza as extension and thought; we speak of them as matter and force. The "extended" (or space-occupying) is matter; and in Spinoza "thought" does not mean a particular function of the human brain, but energy in the broadest sense. While hylozoistic monism conceives the human soul in this sense as a special form of energy, the current dualism or vitalism affirms, on the authority of Kant, that psychic and physical forces are essentially different; that the former belong to the immaterial and the latter to the material world. The theory of psycho-physical parallelism, as developed especially by Wundt (1892), gives a very sharp and definite expression to this dualism; it says that "physical processes correspond to every psychic phenomenon, but the two are completely independent of each other and have no natural causal connection."

This wide-spread dualism finds its chief support in the difficulty of directly connecting the processes of sensation with those of movement; and so the one is regarded as a psychic and the other as a physical form of energy. The conversion of the outer stimulus (waves of light, sound, etc.) into an inner sensation (sight or hearing) is regarded by monistic physiology as a conversion of force, a transformation of photic or acoustic energy into specific nerve-energy. The important theory of the specific energy of the sensory nerves, as formulated by Johannes Müller, forms a bridge between the two worlds. But the idea which these sensations evoke, the central process in the thought-organ or phronema that brings the impressions into consciousness, is generally regarded as an incomprehensible mystery. However, I have endeavored to prove, in the tenth chapter of the _Riddle_, that consciousness itself is only a special form of nervous energy, and Ostwald has lately developed the theory in his _Natural Philosophy_.

The processes of movement which we observe in every change of one form of energy into another, or every passage of potential into actual energy, are subordinate to the general laws of mechanics. The dualist metaphysic has rightly said that the mechanical philosophy does not discover the inner causes of these movements. It would seek these in psychic forces. On our monistic principles they are not immaterial forces, but based on the general sensation of substance, which we call _psychoma_, and add to energy and matter as a third attribute of substance.

The difficulty of combining our monism with Spinoza's doctrine of substance is met by detaching the idea of energy from sensation and restricting it to mechanics, so as to make movement a third fundamental property of substance with matter (the "extended") and sensation (the "thinking"). We may also divide energy into active (= will in the sense of Schopenhauer) and passive (= sensation in the broadest sense). As a matter of fact, the energy to which modern energism would reduce all phenomena has not an independent place in Spinoza's system besides sensation; the attribute of thought (the psyche, soul, force) comprises the two. I am convinced that sensation is, like movement, found in all matter, and this trinity of substance provides the safest basis for modern monism. I may formulate it in three propositions: (1) No matter without force and without sensation. (2) No force without matter and without sensation. (3) No sensation without matter and without force. These three fundamental attributes are found inseparably united throughout the whole universe, in every atom and every molecule. In view of the great importance of this view for our hylonistic system of monism, it may be well to consider each of these three attributes in connection with the law of substance.

_A._ MATTER.--As extended substance, matter occupies infinite space, and each individual body forms a part of the universe as real substance. The law of the conservation of matter teaches us that the sum of matter is eternal and unchangeable. This applies equally to the various kinds of matter which we call the chemical elements, or ponderable matter, and to the ether that fills the spaces between the atoms and molecules, or imponderable matter. The mischievous depreciation of matter (and the consequent disdain of materialism) and its antithesis to "spirit" is partly due to the use of such phrases as "raw" and "dead" matter, and partly to the deep-rooted mysticism we have inherited from barbaric ancestors, and find it hard to shake off.

_B._ ENERGY.--All parts of the substance that fills infinite space are in constant and eternal motion. Every chemical process and every physical phenomenon is accompanied by a change in the position of the particles which compose the matter. The law of the conservation of energy teaches us that the sum of force or energy that is ever at work in the universe is unchangeable. In the formation or decomposition of a chemical compound the particles of matter move about, and so in every mechanical, thermic, electric, and other process. The changes that take place depend on a constant change of force, both in organic and inorganic bodies; one form of force is converted into another without a particle of the whole being lost. This law of the conservation of force has lately been called, as a rule, the conservation of energy (or the principle of energy) since the ideas of force and energy have been more clearly distinguished in physics; energy is now usually defined as the product of force and direction. It must be noted, however, that the word "energy" (as an equivalent to "work" in the physical sense) is still used in many different senses, as is also the word "force." Others define energy as "work or all that comes of work and may be converted into work." One particular school of voluntarism (Wundt) reduces the motive-force of energy to will. Crusius said in 1744: "Will is the dominating force in the world." And Schopenhauer defines the world (or substance) as "will and presentation."

_C._ SENSATION.--In describing sensation (in the broadest sense) as a third attribute of substance, and separating "sensitive substance" from energy as "moving substance," I rely on the observations I made in the thirteenth chapter of the _Riddle_ on sensation in the organic and inorganic world. I cannot imagine the simplest chemical and physical process without attributing the movements of the material particles to unconscious sensation. In this sense the chemist speaks every day of a sensitive reaction, and the photographer of a sensitive plate. The idea of chemical affinity consists in the fact that the various chemical elements perceive the qualitative differences in other elements, experience "pleasure" or "revulsion" at contact with them, and execute their specific movements on this ground. The sensitiveness of the plasm to all kinds of stimuli, which is called "soul" in the higher animals, is only a superior degree of the general irritability of substance. Empedocles and the panpsychists spoke in the same sense of sensation and effort in all things. As Nägeli said: "If the molecules possess something that is related, however distantly, to sensation, it must be comfortable to be able to follow their attractions and repulsions; uncomfortable when they are forced to do otherwise. Thus we get a common spiritual bond in all material phenomena. The mind of man is only the highest development of the spiritual processes that animate the whole of nature." These views of the distinguished botanist fully agree with my monistic principles.

When sensation in the widest sense (as _psychoma_) is joined to matter and energy as a third attribute of substance, we must extend the universal law of the permanence of substance to all three aspects of it. From this we conclude that the quantity of sensation in the entire universe is also eternal and unchangeable, and that every change of sensation means only the conversion of one form of psychoma into other forms. If we start from our own immediate sensations and thoughts, and look out on the whole mental life of humanity, we see through all its continuous development the constancy of the psychoma, which has its roots in the sensations of each individual. This highest achievement of the work of the plasm in the human brain was, however, first developed in the sensations of the lower animals, and these are in turn connected by a long series of evolutionary stages with the simpler forms of sensation that we find in the inorganic elements, and that reveal themselves in chemical affinity. Albrecht Rau expressly says in his excellent _Sensation and Thought_ (1896) that "perception or sensation is a universal process in nature. This involves, moreover, the possibility of reducing thought itself to this universal process." Recently Ernst Mach has said, in his _Analysis of Sensation and the Relation of the Physical to the Psychical_, that "sensations are the common elements of all possible physical and psychic occurrences, and consist simply in the different mode of the combination of the elements and their dependence on each other." It is true that Mach, in his one-sided emphasis of the subjective element of sensation, goes on to form a similar psychomonism to that of Verworn, Avenarius, and other recent dynamists; but the fundamental character of his system is purely monistic, like the energism of Ostwald.

In thus uniting sensation with force and matter as an attribute of substance, we form a monistic trinity, and are in a position to do away with the antitheses that are rigidly maintained by dualists between the psychic and the physical, or the material and the immaterial world. Of the three great monistic systems materialism lays too narrow a stress on the attribute of matter, and would trace all the phenomena of the universe to the mechanics of the atoms or to the movements of their ultimate particles. Spiritualism, with equal narrowness, builds on the attribute of energy; it would either explain all phenomena by motor forces or forms of energy (energism), or reduce them to psychic functions, to sensation or psychic action (panpsychism). Our system of hylonism (or hylozoism) avoids the faults of both extremes, and affirms the identity of the psyche and the physis in the sense of Spinoza and Goethe. It meets the difficulties of the older theory of identity by dividing the attribute of thought (or energy) into two co-ordinate attributes, sensation (psychoma) and movement (mechanics).

XX

MONISM

Defence of monism--Pure and applied science (theoretic and practical reason)--Pure (theoretical) sciences: physics, chemistry, mathematics, astronomy, geology; biology, anthropology, psychology, philology, history--Applied (practical) sciences: medicine, psychiatry, hygiene, technology, pedagogics, ethics, sociology, politics, jurisprudence, theology--Antinomy of the sciences--Rational and dogmatic disciplines--Correlation of the sciences--Faculties--Reform of education--The ideal world--Harmony of monism.

Now that we have reached the end of our long journey, we may take a general survey of the path we have pursued, and say how far we owe our progress to the monistic philosophy. In doing so, we shall at once justify our own point of view and indicate the relation of biology to the other sciences. I feel the more bound to do this as the present volume is not only a necessary supplement to the _Riddle_, but at the same time my last philosophic work. At the end of my seventieth year I would supply some of the defects of the _Riddle_, answer some of the most stringent criticisms directed against it, and as far as possible complete the philosophy of life at which I worked for half a century.

In inviting my readers to accompany me once more through the broad domain of the monistic philosophy I must, as their modest guide, show scientific justification at the narrow entrance--produce, so to say, the ticket of admission to this investigation. The academic philosophy which still controls the German universities watches every door with jealous eyes, and has an especial concern to keep out modern biology. Official German philosophy is still for the most part taken up with a mediæval metaphysic and the dualism of Kant, the openly dogmatic character of which it greets as "criticism." In the course of the forty years during which I have taught as ordinary professor of zoology at Jena I have had occasion to assist at several hundred examinations of doctors, teachers, etc., in which distinguished representatives of philosophy were examiners. I saw that nearly always the chief stress was laid on a kind of conceptual gymnastics and self-observation, and on the correct knowledge of the innumerable errors which the (mainly dualistic) leaders of ancient and modern philosophy have left us in their vast literature. The central feature of the whole scheme is Kant's theory of knowledge, the defects and one-sidedness of which I have treated in the first and nineteenth chapters. In psychology a most extensive knowledge of psychic powers on the basis of the introspective method is demanded; the physiological analysis of the "soul" and the anatomic study of the phronema are carefully avoided, as are also the comparative and genetic study of the mind. Many of our metaphysicians go even farther and regard philosophy as a separate science--a sublime "mental science," quite independent of the common empirical sciences. One is tempted to quote the saying of Schopenhauer: "It is a sure sign of a philosopher that he is not a professor of philosophy." In my opinion, every educated and thoughtful man who strives to form a definite view of life is a philosopher. As queen of the sciences, philosophy has the great task of combining the general results of the other sciences, and of bringing their rays of light to a focus as in a concave mirror. The various tendencies of thought that arise in such numbers have all a right to scientific respect and discussion, the monistic minority no less than the dualistic majority. We have to inquire, then, how far monism has succeeded in gaining firm foothold in the various fields of science, and we may begin with a distinction between pure (theoretical) and applied (practical) science.

Pure philosophy aims at a knowledge of the truth by means of pure reason, as I explained in the first chapter. However, this theoretical philosophy finds itself in most of the sciences in direct and frequently important relations to practical life, and so in the form of applied philosophy becomes a weighty factor in civilization. In this the real claims of practical life are often in contradiction to the ideal tenets of the scientifically grounded theory. In such cases, in my opinion, the pure pursuit of the truth must take precedence of applied philosophy. I thus dissent entirely from the view of Kant, who expressly gives precedence to practical reason, and subordinates theoretical reason to it. Kant's error was fated to have a terrible influence, because the dominant authorities in Church and state eagerly embraced it to insure everywhere the supremacy of the dogmas of practical reason over the attainments of pure critical reason.

From the point of view of natural monism we may take physics in the wider sense as the fundamental science. The term _physis_ (the Greek equivalent of the Latin "nature"), in its original meaning, comprises the whole knowable world--Kant's _mundus sensibilis_. His supersensual or "intelligible" world is, on his own definition, the object of faith, not knowledge. It is very remarkable to find a thinker like Kant contradicting himself already in his fundamental distinction of the two worlds. How can the supersensual world, with its three central mysteries (God, freedom, and immortality), be described as intelligible (_i.e._, knowable) when it is proved by pure reason that the human mind is incapable of knowing it, or of forming any positive or negative idea of it? _Lucus a non lucendo!_ We may, therefore, leave this supernatural metaphysical world to faith and fiction, and confine our studies to the real physical world, nature. The idea of physics as a comprehensive natural philosophy, as it was conceived in classic Greece, has been more and more restricted in the course of time. To-day it is generally taken to mean the science of the phenomena of inorganic nature, their empirical determination by observation and experiment (experimental physics), and their reduction to fixed natural laws and mathematical formulæ (theoretical or mathematical physics). Of late a distinction has been drawn between the physics of mass and the physics of ether; the one deals with mechanics, the movement and equilibrium of ponderable matter, of solid, fluid, and gaseous bodies (statics and dynamics, gravitation, acoustics, meteorology); the other is occupied with the phenomena of ether (or imponderable matter) and its relations to mass (electricity, galvanism, magnetism, optics, and calorics). In all these branches of inorganic physics the monistic view is now generally received, and all attempt at dualistic explanation abandoned.

The vast department of chemistry, which has now become so important both for theoretical and practical purposes, is really only a part of physics. But while modern physics restricts itself to the study of inorganic forms of energy and their conversions, chemistry, as the science of matter, takes up the study of the qualitative differences between the various kinds of ponderable matter. It divides ponderable bodies into some seventy-eight elements, the relations of which to each other have been determined in the periodic system of the elements, and their probable common origin from some primitive matter (prothyl) been shown. The constant features of chemical combinations which have been established by the analysis and synthesis of the elements, and especially the law of simple and multiple proportions discovered in 1808, led to the empirical determination of the atomic weight of the elements and to the chemical theory of the atom. The acceptance of these atoms (as space-filling separate particles of matter--however we may regard them in other respects) is an indispensable hypothesis in chemistry, like the hypothesis of the molecule in physics. Modern dynamism (or energism) is wrong when it thinks it can dispense with these hypotheses and replace the atoms by the notion of immaterial non-spatial points of force. However, in both the dynamic and the material school monism is retained in every department of chemistry.

Modern science considers the ultimate aim of all research to be the exact determination of phenomena in measure and number, or the reduction of all general knowledge to mathematically formulated laws. As the great Laplace established his system mathematically, it has lately been claimed that a comprehensive (ideal) Laplace-mind could embrace the whole past, present, and future of the universe in a single gigantic mathematical formula. Kant has expressed this exaggerated estimate of mathematics in the phrase: "Every science is only true science in proportion as it is amenable to mathematical treatment"; and to this he has added the second error that the mathematical axioms (being necessary and universal truths) belong to the _a priori_ constitution of the mind, and are independent of experience (_a posteriori_). However, John Stuart Mill and others have shown that the fundamental ideas of mathematics are acquired originally, like those of any other science, by abstraction from experience; and the modern phylogeny of the mind has confirmed this empirical view. We must remember, moreover, that mathematics deals only with quantitative relations in time and space, and not with the qualitative features of bodies. In fact, Kant himself showed that mathematics only answers for the absolute _formal_ correctness of conclusions it draws from given premises, and has no influence on the premises themselves. Hence, when we examine the abstract thinking-power of the phronema in its mathematical operations physiologically and phylogenetically, we find that even this "exact fundamental science" is only accessible to pure monism and excludes all dualism. The great regard which mathematics enjoys as an exact science in all branches of knowledge is chiefly due to its _formal accuracy_, and to the possibility of expressing infallibly spatial and time quantities in number and mass.

Astronomy is one of the older sciences that took definite shape thousands of years ago, and received a solid mathematical foundation. Observations of the movements of the planets and eclipses of the sun were conducted by the Chinese, Chaldeans, and Egyptians several thousand years before Christ. Christ himself had no more suspicion of these great cosmological discoveries than of the systems which the Greek natural philosophers had built up three hundred to six hundred years before his birth. After Copernicus had destroyed the geocentric system in 1543, and Newton had provided a mathematical basis for the new heliocentric system by his theory of gravitation in 1686, cosmogony was firmly established in a monistic sense by the _General Natural History of the Heavens_ of Kant, and the _Mécanique Céleste_ of Laplace. Since that time there has been no question of the conscious action of a Creator in any part of astronomy. Astrophysics has enlarged our knowledge of the physical features, and astrochemistry (by means of spectrum analysis) of the chemical nature of the other heavenly bodies. The monism of the physical universe has now been established.

Geology was not developed into an independent science until towards the end of the eighteenth century, and did not extinguish the earlier notion of the creation of the earth until after 1830, when the principle of continuity and evolution was established. The oldest part of the science is mineralogy; the great practical value of the rocks, and especially the metals obtained from them, having appealed to man's interest thousands of years ago. In the Stone Age, Bronze Age, Iron Age, etc., the material for weapons and tools was provided by stone and metal. Afterwards the development of mining led to a closer acquaintance with these metals. But no notice was taken of the fossil remains of animals and plants until the close of the Middle Ages. It was not until the eighteenth century that students began to perceive the great significance of these "creation-medals," and at the beginning of the nineteenth paleontology arose as an independent science, and proved equally important to geology and biology. Other branches of geology, such as crystallography, have also made considerable progress during the last half-century, with the aid of physics and chemistry. All these sections of geology, especially geogeny, or the science of the natural development of the earth, are now recognized to be purely monistic sciences.

In the five branches of science I have enumerated, pure monism has been universally and exclusively admitted (as far as they relate to inorganic nature) in the second half of the nineteenth century. There is no question in them to-day of the wisdom and power of the Creator. This is equally true of geology, astronomy, mathematics, chemistry, and physics. It is otherwise with the remaining sciences which deal with organic nature; in these we have not yet succeeded in giving a physical explanation and mathematical formulation of all phenomena. Hence vitalism enters with its dualistic notions, and splits the science into two different branches--natural science (physics in the wider sense) and mental science (metaphysics); fixed natural laws are supposed to rule only in the former, while in the latter we still have the "freedom" of the spirit and the supernatural. This applies, first of all, to biology in the broadest sense (including anthropology and all the sciences that relate to man). In the preceding chapters of biological philosophy we have sought to refute vitalism in every form, and to secure the exclusive acceptance of monism and mechanicism in every branch of the science of life.

Anthropology is still, as it has been for centuries, taken in many different senses. In the widest sense, it embraces the whole vast science of man, just as zoology (in my opinion) deals with all parts of the animal world. Since I regard anthropology as a part of zoology, I naturally extend the principles of monism to both. However, this general monistic conception of the science of man has met with only a restricted acceptance up to the present. As a rule, the term "anthropology" is restricted to the natural history of man, which includes the anatomy and physiology of the human organism, embryology, prehistoric research, and a small part of psychology. But this "official anthropology," as most of our anthropological societies (especially in Germany) conceive it, generally excludes phylogeny, the greater part of psychology, and all the mental sciences, which are regarded as metaphysical in the narrower sense. I endeavored to show in my _Anthropogeny_ thirty years ago that man (as a placental mammal of the order of primates) is no less unified an organism (with body and soul) than any other vertebrate, and that, therefore, every aspect of his being should be dealt with monistically.

As is well known, the views of experts and laymen alike are very much divided as to the place of psychology in the scheme of the sciences. The great majority of the professional psychologists, and of educated people generally, adhere still to the antiquated dogma, with its religious foundation, that man's soul is immortal and an independent immaterial entity. This dualistic view has been supported in the schools especially by the authority of Plato, Descartes, and Kant; in religion by the authority of Christ, Paul, and Mohammed; in education and the state by the authority of most governments; and in physiology by most of the older, and even some recent, physiologists. On this view, psychology is a special mental science, having only an external and limited connection with natural science. But modern comparative and genetic psychology, the anatomy and physiology of the brain, have, in the course of the last forty years, established the monistic view that psychology is a special branch of cerebral physiology, and that therefore all its parts and their application belong to this section of biology. The soul of man is a physiological function of the phronema. As I have fully explained the monistic conception of psychology in chapters vi.-xi. of the _Riddle_, and supported it with all the arguments of anatomy, physiology, ontogeny, and phylogeny in my _Anthropogeny_, I need not go further into the subject.

The science of language shares the fate of its sister, psychology; by one section of its representatives it is taken monistically as a natural science, and by another section it is dualistically conceived as a branch of mental science. On the old metaphysical view, speech was regarded as an exclusive property of man, either a gift of the gods or an invention of social man. But in the course of the nineteenth century the monistic and physiological position that speech is a function of the organism, and has been gradually developed like all other functions, has been established. The comparative psychology of the higher animals showed that in various classes the thoughts, feelings, and desires of the gregarious animals are communicated partly by signs or touch, partly by sounds (the chirrup of the cricket, the cry of the frog, the whistle of many reptiles, song of birds and singing-apes, roaring of carnivora and ungulates, etc.). The ontogeny of speech showed that its gradual development in the child is (in accordance with the biogenetic law) a recapitulation of its phylogenetic process. Comparative philology taught that the languages of the different races have been formed polyphyletically, or independently of each other. The experimental physiology and pathology of the brain showed that a definite small region of the cortex (the Broca fissure) is the centre of speech, and that this central organ, in conjunction with other parts of the phronema and the larynx (the peripheral organ), produces articulate speech.

Historical science is, like philology or psychology, still conceived in different senses by experts. Very often history is wrongly taken to mean the record of events that have occurred in the course of the development of civilized life--the history of peoples and states (humorously described as "the history of the world"), of civilization, of morals, etc. This is merely an anthropocentric feeling that in the strictly scientific sense "history" can only be used for the record of man's doings. In this sense history is opposed to nature, the one dealing with the province of morally free phenomena (with preconceived aim), and the other comprising the province of natural law (without preconceived aim). As if there were no "natural history," or as if cosmogony, geology, ontogeny, and phytogeny were not historical sciences! Although this dualistic and anthropistic view still prevails in our universities, and state and Church protect the venerable tradition, there can be no doubt that sooner or later it will be replaced by a purely monistic philosophy of history. Modern anthropogeny shows us the intimate connection between the evolution of the human individual and that of the race; and by means of prehistoric and phylogenetic research it joins what is called the history of the world to the stem-history of the vertebrates.

Medicine belongs to the front rank of practical or applied sciences. In its long and interesting history it teaches how it is only a monistic knowledge of nature, not a dualistic notion of revelation, that affords the foundations of true science and the profitable application of this to the most important aspects of practical life. Medicine was originally the business of the priests, and for thousands of years it was under the influence of mystic and superstitious ideas which were connected with religious dogmas. However, two thousand years ago the great physicians of classic antiquity made a serious effort to provide a solid base for medical practice by a thorough anatomic and physiological study of the human frame. But in the general reaction of the Middle Ages superstitious and miraculous ideas once more defeated independent scientific investigation. Disease was supposed to be the work of evil spirits (as Christ thought) which had to be exorcised. Miracles are still thought to take place, even in cultured circles. I need only mention the wonders of patent medicines, magnetic cures, Christian Science, and other charlatanry. However, the great development of science in the nineteenth century, especially the astonishing advance of biology about the middle of the century, gradually shaped medicine into the monistic science which assuages so much pain and suffering in humanity to-day. Pathology, the science of disease, and therapeutics, the rational science of healing, are grounded now on the safe methods of physics and chemistry and a thorough knowledge of the human organism. Disease is no longer regarded as a special entity that comes on the body like an evil spirit or mysterious organism, but is conceived as a baneful disturbance of its normal activity. Pathology is only a branch of physiology; it studies the changes that take place in the tissues and cells under abnormal and dangerous conditions. When the causes of these changes are poisons or foreign organisms (such as bacteria or amœbæ), the art of healing has to remove them and restore the normal equilibrium of the functions.

The science of mental disease is a special branch of medicine; it has the same relation to it as psychology has to physiology. However, as pathological psychology it deserves special consideration, not only on account of its extreme practical importance, but also because of its theoretical interest. The misleading dualist idea of body and soul that has perverted our notions of mental life from the oldest times has led people to regard mental disorders as special phenomena, at one time directly as evil spirits that enter from without into the human body, at another time as mysterious dynamic occurrences affecting the mystic being of the soul (independently of the body). These dualistic and still wide-spread and mischievous errors have caused the most fatal mistakes in the treatment of mental disease; they have had the most unfortunate effect on juristic and social and other aspects of practical life. But the ground has been cut from under these irrational and superstitious ideas by modern psychiatry, which regards all mental disease as a disorder of the brain, and traces it to changes in the cortex that lie at the root of all psychoses (delusions, lunacy, etc.). As we call this central organ of mind the phronema, we may say: Psychiatry is the pathology and therapeutics of the phronema. In many disorders we have already succeeded in anatomically and chemically tracing the changes in the psychic or phronetal cells (the neurona in the phronema). These acquisitions of the pathological anatomy and physiology of the phronema have a great philosophic interest, because they throw a good deal of light on the monistic conception of psychic life. As the greater part (sixty to ninety per cent.) of these diseases are hereditary, and they have mostly been acquired gradually by the ancestors of the patient, they also afford clear proof of progressive heredity, or the inheritance of acquired characters.

Thousands of years ago, when barbaric races began to adapt themselves to civilized life, they had a concern for their bodily health and strength. In classic antiquity the care of the body by baths, gymnastic exercises, etc., was greatly developed, and connected with religious ceremonies. The splendid aqueducts and baths of Greece and Rome show how much importance they attached to the external and internal use of water. The Middle Ages brought reaction in this province like so many others. As Christianity depreciated this life and said it was merely a preparation for the life to come, it led to a disdain of culture and of nature; and as it regarded man's body only as the temporary prison of his immortal soul, it attached no importance to the care of it. The frightful plagues that swept away millions of men in the Middle Ages were only fought with prayer, processions, and other superstitious devices, instead of with rational hygienic and sanitary measures. We have only gradually learned to discard this superstition. It was not until the second half of the nineteenth century that a sound knowledge of the physiological functions and environment of the organism induced people once more to have a concern for bodily culture. All that modern hygiene now does for the public health, especially the improvement of the dwellings and food of the poorer classes, the prevention of disease by healthier habits, baths, athletics, etc., can be traced to the monistic teaching or reason, and is altogether opposed to the Christian belief in Providence and the dualism connected therewith. The maxim of modern hygiene is: God helps those who help themselves.

The remarkable progress of technical science in the nineteenth century, which has stamped our age as "an age of machinery," is a direct consequence of the immense advance of theoretical science. All the privileges and comforts which modern life gives us are due to scientific discoveries, especially in physics and chemistry. We need only recall the enormous importance of steam and electric machinery, modern mining, agriculture, and so on. If by these means modern industry and international commerce have prospered beyond all expectations, we owe this to the practical application of empirical truths. "Mental science" and metaphysical speculation have had nothing to do with it. There is no need of further proof that all the technical sciences have a purely monistic character, like their exact sources, physics and chemistry.

The scientific development of education is one of the greatest tasks of modern civilization. The ideas that are impressed on the mind in early youth are most persistent, and generally determine the direction of thought and conduct for the whole of life. Hence we find the struggle between the two philosophic tendencies assuming the greatest practical importance in this department. As the priests were, thousands of years ago, in the first stages of civilization, the sole trainers of the growing mind, they had charge of the school as well as of medicine. Religion was made the chief foundation of instruction, and its doctrines were the moral guide for the whole of life. The isolated attempts that were made by monistic philosophy in ancient times to destroy this theistic superstition had no effect on the education of the young. In this the dualistic principles of Plato and Aristotle prevailed, their metaphysical theories being blended with the teaching of the Church. In the Middle Ages the power of the Roman priesthood enforced them everywhere. And, although a good deal of this teaching lost its prestige at the Reformation, the influence of the Church on the school was maintained down to our own time. The spiritual power of the Church finds a useful ally in this in the conservative attitude of most governments. Throne and altar support each other; both dread the advance of scientific inquiry. In face of this powerful dualistic alliance, supported by the mental apathy of the masses and a convenient blind submission to authority, the monistic system has a difficult position to maintain. It will only gain solid ground in education when the school is divorced from the Church and scientific knowledge is made the foundation of the curriculum. I have pointed out in the nineteenth chapter of the _Riddle_ the guiding principles to be followed in this reform of education in opposition to the influence of Church and state.

As we have dealt in the eighteenth chapter with morals and their development from habit and adaptation, we need only mention here the contradiction that we still find between the monistic claims of pure reason and the dualistic claims of practical reason. This has been largely sustained by Kant's teaching, but his categorical imperative has been completely refuted by modern science. The metaphysical grounding of morality on free will and ethical intuitions (_a priori_) must be replaced by a physiological ethic, based on monistic psychology. As this can no more recognize a moral order of the world in history than a loving Providence in the life of the individual, the monistic morality of the future must be reducible to the laws of biology, and especially of evolution.

The great importance that attaches to the new science of sociology is due to its close relations to theoretical anthropology and psychology on the one hand, and to practical politics and law on the other. When we take it in the wider sense, human sociology joins on to that of the nearest mammals. The family life, marriage, and care of the young in the mammals, the formation of herds in the carnivora and ungulates and of troops in the social apes, lead on to the looser associations of savages and barbarians, and from these to the beginnings of civilization. The history of these associations is connected with the social rules that govern the intercourse of smaller and larger communities. In the biological reduction of social rules to the natural laws of heredity and adaptation, dynamic sociology (as Lester Ward has called it) proceeds on purely monistic lines, while in social intercourse itself we still find a good deal of dualism. How little truth and nature count for in our cultured society, how much hypocrisy and insincerity have to do with social rules, has been well shown by Max Nordau in his _Conventional Lies of Civilization_.

Politics is closely connected with sociology on the one hand and law on the other. As internal politics it controls the organization of the state by a constitution; as external or foreign politics it directs the relations of states to each other. In my opinion, pure reason should prevail in both departments; the relations of the citizens to each other and to the whole should be regulated by the same ethical principles that we recognize in personal intercourse. We are, unfortunately, very far from this ideal in the life of a modern state. Brutal egoism rules in foreign politics; every nation thinks only of its own advantage, and furthers it with all its military and other resources. Domestic politics is still largely directed by the barbaric prejudices of the Middle Ages. Great struggles are in progress between the central government and the mass of the people. Both parties spend themselves in fruitless conflicts; yet reason in the life of the state suffers more than its special political complexion. "Whether the state shall be a monarchy or a republic, aristocratic or democratic, are subordinate questions. The great question is: Shall the modern state be spiritual or secular? Shall it be governed _theocratically_ by irrational beliefs and clerical arbitrariness, or _nomocratically_ by rational laws and civic right?" (_Riddle_, chapter i.).

In the science of law, too, we find the prevalence of the dualistic principles that have come down from the Middle Ages and antiquity, and have acquired a certain sacredness by blending with the teaching of the Church. Kant's dualism is again found to be at work, influencing the ideas of jurists and statesmen. With it we find in our codes many carefully preserved relics of mediæval superstition. A great deal of harm is done by this religious influence. Every day we read in the papers of curious deliverances in the lower and higher courts at which every thoughtful man can only shake his head. Here also there will be no solid improvement until the education of jurists includes a thorough training in anthropology and psychology as well as in the code.

Theology has stood at the head of the four venerable "faculties" at our universities for centuries. It still holds this place of honor, as the Church, the organ of practical theology, continues to exercise a profound influence on life. In fact, most of the other branches of applied science--especially jurisprudence, politics, ethics, and pedagogics--are still more or less affected by religious prejudices. The chief of these is the idea of God conceived in some form or other as the Supreme Being; as Goethe says, "Every one calls the best he knows his God." However, the idea of God is not the chief feature of all religions. The three greatest Asiatic religions--Buddhism, Brahmanism, and Confucianism--were at first purely atheistic; Buddhism was at once idealistic and pessimistic, whence Schopenhauer regarded it as the highest of all religions. On the other hand, belief in a personal God is the central feature of the three great Mediterranean religions. This anthropomorphic God is conceived in a hundred forms in the various sects of the Mosaic, Christian, and Mohammedan religions, but his existence remains one of the chief articles of faith. No evidence of his existence is to be found; this was very ably shown by Kant, although he thought that practical reason postulated it. All that revelation is supposed to teach us on the matter belongs to the region of fiction. The whole field of theology, especially dogmatic theology, and the whole of the Church teaching based on it, are based on dualistic metaphysics and superstitious traditions. It is no longer a serious subject of scientific treatment. On the other hand, comparative religion is a very important branch of theoretical theology. It deals with the origin, development, and significance of religion on the basis of modern anthropology, ethnology, psychology, and history. When we study without prejudice the results of these sciences bearing on religion, theology turns out to be pantheism, in the sense of Spinoza and Goethe, and thus monism becomes a connecting link between religion and science.

This brief survey of the twenty chief branches of modern science and their relation to monism and dualism shows that we are face to face with great contradictions, and that we are still far from the harmonious and successful adjustment of these differences. They are partly due to a real antinomy of reason in the Kantist sense--an antithesis in ideas, in which the positive seems to be just as capable of proof as its contradictory. But, for the most part, this unfortunate antinomy in the sciences is connected with their historical development. Pure reason, the highest quality of civilized man, was gradually evolved from the intelligence of the savage, and this in turn from the instincts of the apes and lower mammals; and many relics of its former lower condition remain to-day, and have, through practical reason, a most prejudicial influence on science. These dualistic prejudices and irrational dogmas--intellectual residua of the primitive condition of the race, fossil ideas and rudimentary instincts--still pervade the whole of modern theology, jurisprudence, politics, ethics, psychology, and anthropology. If we glance at the whole field of modern science at the beginning of the twentieth century in this connection, we can distribute its twenty sections into three groups--rational (purely monistic), semi-dogmatic (half-monistic), and dogmatic (predominantly dualistic) disciplines.

The following may be classed as rational or purely monistic sciences, in which no competent and thoroughly expert representative now admits dualistic considerations: of the pure or theoretical sciences, physics, chemistry, mathematics, astronomy, and geology; of the applied or practical sciences, medicine, hygiene, and technology. On the other hand, in the semi-dogmatic sciences we still find a mixture of monistic and dualistic ideas in the appreciation of their aims and objects, one or the other prevailing according to the party position or personal training of the individual representative. This is the case with most of the biological sciences, biology (in the broadest sense), anthropology, psychology, philology, history, psychiatry; and of the applied sciences, pedagogics and ethics. The two latter sciences form a transition to the four purely dogmatic sciences in which the traditional dualism is still paramount: sociology, politics, jurisprudence, and theology. In these branches of science mediæval traditions retain a good deal of their power. Most of their official representatives cling to prejudices and superstitions of all sorts, and very slowly and gradually admit the acquisitions of pure reason as embodied in monistic anthropology and psychology. The intellectual life was in many respects more advanced at the beginning of the nineteenth than of the twentieth century.

This classification of the chief branches of knowledge in their relation to philosophy, the comprehensive science of general truths, is naturally only a provisional and personal sketch. It is especially difficult from the circumstance that all the sciences have very complex relations to each other, and have undergone many changes as to their aims and subjects in the course of their historical development. I will only point out that a good deal of science--in fact, the rational sciences with exact mathematical basis--have now been completely won over to monism; and in the semi-dogmatic sciences it is gaining ground from day to day, so that we may hope sooner or later to see the four dogmatic sciences also, the strong bulwarks of dualism--sociology, politics, jurisprudence, and theology--succumb to monism. For the ultimate aim of all the sciences can only be the unity of their underlying principles, or their harmonious unification by pure reason.

It is now more and more generally acknowledged in educated countries that a complete reform of our educational curriculum is needed, both in elementary and secondary schools and at the universities. The great struggle between two different tendencies assumes larger proportions every day. On the one hand, most governments, following their conservative instinct, cling as far as possible to mediæval traditions, and find support in the dogmatic teaching of theology and jurisprudence. On the other hand, the representatives of pure reason seek to get rid of these fetters, and to introduce the empirical and critical methods of modern science and medicine into what are called the mental sciences. The opposition between the two parties is accentuated by their different sociological tendencies. Liberal humanists claim that the freedom and education of all men is the aim of progressive evolution, in the conviction that the free development of the personality of each individual is the surest guarantee of happiness. To conservative governments this is a matter of indifference; they look on the individual citizens, in accordance with the manifold division of labor, merely as so many screws and wheels in the great organism of the state. The "upper ten thousand" naturally think of their own welfare first, and desire to keep all higher education to themselves. But in the light of pure reason the state is not an end in itself; it is a means to insure the prosperity of the citizens. To each of these, whatever their condition, the opportunity should be afforded of acquiring the higher education and developing their talents. Hence in education we should impart a general outlook on all the sides of human life. Each should acquire the elements of science, not only of physics and chemistry, but also of biology and anthropology. On the other hand, the predominance of the classical training over modern ought to be restricted. Every student and every faculty should be occupied with only philosophy and science in the first sessions, and not take up special studies until afterwards.

At the close of the _Riddle_ I brought out in clear relief the antagonism between modern monism and traditional dualism, but also pointed out that

this strenuous opposition may be toned down to a certain degree on clear and logical reflection--may, indeed, be converted into a friendly harmony. In a thoroughly logical mind, applying the highest principles with equal force in the entire field of the cosmos--in both organic and inorganic nature--the antithetical positions of theism and pantheism, vitalism and mechanism, approach until they touch each other. Unfortunately, consecutive thought is a rare phenomenon in nature.

This conciliatory disposition has grown stronger and stronger in me. Every year increases my belief that the dualism of Kant and the prevalent metaphysical school must give way to the monism of Goethe and the rising pantheistic tendency. In this we do not lose sight of our ideals. On the contrary, our "realist philosophy of life" teaches us that they are rooted deep in human nature. While occupying ourselves with the ideal world in art and poetry, and cultivating the play of emotion, we persist, nevertheless, in thinking that the real world, the object of science, can be truly known only by experience and pure reason. Truth and poetry are then united in the perfect harmony of monism.

INDEX

Abiogenesis, 339-358; may still occur, 357.

Abiology, 27, 78.

Abortion, 325.

Abstraction, power of, 316.

Achromin, 140, 142.

Acquired characters, inheritance of, 367-369, 376.

Actinal beauty, 185.

Active movements in organisms, 262.

Adaptation, 415.

Æsthesis, 296, 308.

Æsthetal cells, 14.

Æsthetic selection, 422.

Agassiz on the creation of species, 30.

Agnostic position on the origin of life, 338.

Albumin, 39, 126, 128.

Albuminoids, the, 39, 125, 126.

Algæ, 161, 195, 220.

Alimentary system, the, 227.

Allopola, 174.

Alternation of generations, 253.

Altmann on the structure of plasm, 134.

Altruism, sources of, 115.

Ambulacral system, 280.

Amœboid movements, 268.

Amphigony, 240.

Amphimixis, 244.

Amphithecta, 176.

Angiophyta, 220.

Animal states, 36, 148, 150, 168.

Animals, kindness to, 115; younger than plants, 216.

Animism, 58.

Annelids, motor apparatus of the, 281.

Antheridia, 249.

Anthophyta, 162, 220.

_Anthropogeny, The_, 283, 320.

Anthropogeny, the science of, 321, 332.

Anthropologists and evolution, 321.

Anthropology, 86, 478.

Antivitalism, 50.

Ape, mind in the, 332, 333.

Apes and men, common structure of, 285.

Aphanocapsa, 32, 130, 182, 196, 205.

Apostles' Creed, the, 60-65.

Apotelia, 163.

Apposition, 42.

Archegonia, 249.

Archigony, 341-358; formulation of, 355, 356; repetition of, 356; statement of grounds, 341; theories of, 343-348.

Archiplasm, 129, 142, 158.

Aristotle, 66.

Art, modern development of, 407.

Articulates, motor apparatus of the, 282.

Articulation, 281.

Asexual generation, 241-244.

Assimilation, 42, 211.

Association-centres, 12, 13.

Associational beauty, 185.

Astrolarva, 279.

Astronomy, monism of, 457.

Astrozoon, 280.

Asymmetrical types, 179.

Auditory vesicles, 311.

Autogony, 341.

Autonomous movement, 262.

Bacilli, 200, 201, 202.

Bacon, the founder of empiricism, 7.

Bacteria, the, 157, 198-206, 218, 234, 235; absence of nucleus in the, 200, 201.

Bacteriology, 198.

Baptism, 425, 426.

Barbarians, higher, 395; life of, 394; lower, 394; mental life of, 58; middle, 395; religion of, 58.

Baræsthesis, 309.

Barotaxis, 309.

Bathybius Haeckelii, 207.

Beauty, evolution of the sense of, 188; sources of, 184; stages of, 184-187.

Beggiatoa, 199, 205, 218.

Berzelius on catalysis, 44.

Bilateral-radial types, 177.

Bilateral symmetry, 177.

Bioblasts, 134.

Bio-crystals, 41.

Biogen-hypothesis of Verworn, 46, 137, 138.

Biogens, 102, 128, 137, 192.

Biogenetic law, the, 380-382, 384.

Biogeny, 94, 360.

Biology, division of, 94; sphere of, 27, 78.

Bionomy, 78, 95.

Bionta, 149, 151; virtual, 151; partial, 151.

Biophora, 137.

Biotonus, 103.

Blastoderm, the, 161.

Botanists and zoologists, divergence of, 374.

Brain, as an organ of mind, 25; evolution of the, 22, 327, 328.

Brownian movement, 260.

Bryophyta, 162.

Budding, 242, 243.

Bunge, as vitalist, 50.

Bütschli on the monera, 31; on the structure of plasm, 132.

Calymma, the, 270.

Canon law, the, 324, 325.

Carbon assimilation, 34, 130, 212, 213, 342.

Carbon, importance of, 37, 38.

Caryokinesis, 139, 267.

Caryolymph, 141, 142.

Caryolysis, 268.

Child, mind of the, 90, 323.

Child-soul, study of the, 20.

Children, destruction of incurable, 21, 120.

Chitine, 282.

Chlorophyll, 33, 141, 195, 214.

Chorology, 95.

Chromacea, 32, 130, 137, 157, 182, 194-197; description of the, 194; structure of the, 197.

Chromatella, 33, 343.

Chromatin, 140, 142.

Chromatophora, 33, 343.

Chromoplasts, 141, 196.

Chroococcacea, the, 32, 182.

Chroococcus, 32, 130, 182, 196, 197, 208.

Ciliary movement, 272, 276.

Circulation of the blood, 228.

Civilization, characteristics of, 58-59; evils of, 114; growth of, 334; modern, 335, 402; shades of, 401, 408; stages of, 398; progress of, 469; value of, 309.

Civilized races, higher, 397; life of, 396; lower, 396; middle, 396; mind in, 334.

Cleanliness in antiquity, 464.

Clothing, beginning of, 423; fashions in, 430.

Cnidaria, 224; generation of the, 250, 253.

Cœlenteria, 166, 221, 223, 225.

Cœloma, the, 223, 225.

Cœlomaria, 166, 221, 225.

Cœnobia, 160, 161.

Colloids, nature of, 39.

Colon, the, 226.

Coloring methods, 208.

Conjugation, 246.

Consciousness a function of the brain, 331; development of, 331; nature of, 19, 23, 290, 291.

Conservatism of governments, 73.

Contact-action, 45.

Copulation, 251.

Cormophyta, 165, 167.

Cormus, 36, 148, 150, 154, 168, 184.

Corset, the, 430.

Cortex of the brain, 12, 323, 327, 329.

Cosmic intelligence, 30; monism, 37.

Cosmogony, 360.

Cosmokinesis, 266.

Craniota, mind in the, 326.

Creationism, 337.

Crustacea, parasitic, 237.

Crystals, 41; forms of, 172; growth of, 42, 43; life of, 41; and organisms compared, 35, 40, 41, 43, 44; reproduction of, 44.

Crystallization, 265, 266.

Crystalloids, nature of, 39.

Culmus, the, 165, 183.

Cultivated races, definition of, 397; higher, 400; lower, 398; middle, 399.

Custom, tyranny of, 421.

Cuticle, 146.

Cyanogen, 346.

---- theory, 347.

Cytodes, 33, 157, 192, 194.

Cytology, 128, 190.

Cytophyta, 220.

Cytoplasm, 35, 122, 138, 139, 142, 158, 191.

Cytosoma, 122, 138.

Cytotheca, 145.

Cytula, 244.

Darwin on the origin of life, 338.

Darwinism, 50, 80, 361, 363, 364, 373.

De Bries on heredity, 373.

Death, nature of, 98; of the unicellulars, 99; of the histona, 100; real cause of, 101; total and partial, 105.

Decomposability of plasm, 345.

Descartes' idea of the soul, 16, 18.

Descriptive science, 4, 5, 6.

Design, argument for, 388.

Dialysis, 39.

Diatomes, 41, 182.

Diclinism, 247.

Diœcia, 248.

Disassimilation, 212.

Disease, nature of, 106.

Dissogony, 252.

Division of labor, 35; in the cell, 143, 158; in the organism, 149, 167; in the state, 150, 169.

Divorce, 428, 429.

Dogmatic sciences, 470.

Dominants, the, of Reinke, 264.

Driesch, as vitalist, 51.

Dualism, 81, 91, 433.

Dualistic view of life, 337, 348, 366; of the mind, 332; of morality, 411; of sensation, 446, 447.

Dumas, Louis, as vitalist, 47.

Duty an evolved sense, 413.

Dwarf races, 422.

Dynamism, 85, 110.

Ear, canals in the, 311; the, 312.

Echinoderms, motor organs of the, 279-281.

Ectogenesis, 369.

Education, reform of, 471; struggle over, 465.

Egoism, 115, 403; and altruism, 419.

Elasticity, 310.

Eleatic philosophers, the, 66.

Electric organs, 313.

Electricity, sensation of, 312, 313.

Elements, chemical, 37, 38.

Embryo, legal view of the, 325, 326; mind in the, 325.

Embryology, 20, 21; mechanical, 383.

End of life, 387.

Energism, 85.

Energy as attribute of substance, 446, 449; definition of, 449.

Enzyma, 46, 128.

Epicureanism, 83.

Epitelia, 163.

Epithelium, ciliated and flagellated, 276.

Erect posture, the, 285.

Ergology, 95.

Ergonomy, 35, 150.

Erotic chemotropism, 306.

Eternity hypothesis of life, 338.

Ethic, the perfect, 400.

Ethics, 411.

Eucharist, the, 426.

Excretion, 232, 233.

Experience, importance of, 3, 4.

Experiment, limited use of, 352, 353, 383; nature of, 7, 8.

Experimental science, 4, 8.

Extension, 446, 448.

Eye, the, 298; evolution of, 298, 299.

Faith, 437, 439; natural and supernatural, 54.

Family, evolution of the, 402.

Fashion, 422.

Fechner on sensation, 295; on the universality of life, 340.

Feeling, 296, 308.

Fetichism, 57, 58.

Filar theory of plasm, 134.

Fistella, 344.

Flagelliform movement, 271, 276.

Flame, analysis of the, 28.

Flat-fishes, metamorphosis of, 178.

Flechsig, discoveries of, 13.

Flemming on the structure of plasm, 113.

Food, artificial production of, 400.

Forms of organic structure, 173-184.

Frommann on plasm, 133.

Frothy theory of plasm, 132, 133.

Fungi, 162, 204, 215, 234, 236.

Fungilli, 204, 235.

Gameta, the, 244.

Gastræa theory, the, 223.

Gastræads, 223.

Gastric canal, 228.

Gastro-canal system, 222, 223.

Gastrula, the, 166.

Gemmation, 242, 243.

Genealogy of organisms, 304, 305, 376.

Generation, sexual and asexual, 241-251.

Geogeny, 360.

Geology, historical nature of, 378; monism of, 458.

Geotropism, 310.

Germ-plasm, 143; the theory of, 367, 372.

German mind, Janus character of, 441.

Gills, 229, 230.

Globular shape, origin of, 34.

Glœocapsa, 32, 196, 205.

Goethe, monism of, 442; realism of, 440; scientific studies of, 440, 441.

Gonades, 249.

Gonochorism, 246.

Gonoducts, 250.

Granular theory of plasm, 134.

Gravitation, sensation in, 309.

Growth, 241.

Growth movements, 264.

Habit, 415-417; in inorganic bodies, 417.

Heart, the, 228; work of the, 277.

Heat, sensation of, 300, 301.

Heaven, 109.

Hedonism, 84.

Heliotropism, 298.

Helmholtz on the origin of life, 339.

Heraclitus on life, 28.

Heredity, conservative and progressive, 368; cumulative, 369; theories of, 135, 136, 366.

Hermaphrodism, 245, 246, 258, 259.

Hermaphroditic glands, 249.

Hertwig, O., on the biogenetic law, 382; on the monera, 31.

Heterogenesis, 254.

His, W., theories of, 383.

Histolysis, 106.

Histona, the, 36.

Histonals, 165, 166, 171, 182.

Historical waves, 389.

History, 461; nature of, 9; sources of, 9.

Hofmeister on organic chemistry, 45.

Holosphæra, 173.

Honor, false sense of, 430.

Huxley on organic individuality, 152.

Hyaloplasm, 130, 143.

Hybrids, 255, 256; fertility of, 255.

Hydrostatic movements, 270.

Hygiene, 401, 464.

Hylonism, 82.

Hylozoism, 81, 86, 451.

Hypogenesis, 255.

Hypotheses, nature of, 54; necessity for, 86, 87, 89, 378, 439.

Idealism, theoretical and practical, 84, 92.

Idiocy, 20.

Idioplasm theory, the, 136, 137, 366, 367.

Ileum, the, 226.

Imagination, function of the, 87.

Imbibition energy of plasm, 39.

Imbibition in organisms, 261.

Immaterial world, the, 436, 437.

Immortality, the belief in, 64, 65, 71, 108; of the unicellulars, 99-101.

Incurables and suicide, 118, 119.

Individuality, organic, 149, 152.

Infusoria, movement in the, 268, 269, 272.

Inoculation, 204.

Insanity, increase of, 114, 118, 119.

Insectivorous plants, 304, 305.

Instinct, 418.

Intelligence, 316, 317.

Intercellular matter, 145.

Intussusception, 42.

Ionic philosophers, the, 66.

Irritability, 287, 288, 291, 293.

Isopola, 174.

Kant as natural historian, 9; biological ignorance of, 11, 318, 319; critical views of, 438; contradictory views of, 68, 434, 444; influence of, 25; mechanical views of, 435; moral philosophy of, 412, 413; mystic training of, 443; narrow life of, 443; philosophy of, 68, 69, 74, 434-440; popularity of, 444; theory of knowledge of, 9, 10, 69, 317-319, 332.

Kassowitz on archigony, 355.

Kelvin, Lord, on the origin of life, 339.

Kidneys, the, 233.

Kirchhoff on the work of science, 6.

Knowledge, _a priori_ and _a posteriori_, 11, 24, 317; and faith compared, 54; dualistic theory of, 24; monistic theory of, 12-14.

Kusamaul on the child-soul, 30.

Lamarck, 79.

Lamarck's transformism, 363.

Landscape beauty, 187.

Lange on Kant, 439.

Larvæ, 253.

Law, beginning of idea of, 420; reaction in science of, 401.

Leibnitz, philosophy of, 110.

Leucocytes, 228; and bacteria, 305.

Lichens, 238.

Life, artificial production of, 352, 358; as a flame, 28, 29; constant change of, 386, 387; evolution of, 360-365; length of, 101; nature of, 27, 343; origin of, 337-358; value of, 386-410.

Light, action of, 297-300.

Living substance, 36, 123.

Lobmonera, 206.

Localization of functions, 17, 19, 20; of mental functions, 328, 329.

Locomotion, 275-285; modern progress in, 404.

Lord's Supper, the, 426.

Love, progressive refinement of, 402.

Luminous animals, 312.

Lungs, 230, 231.

Machine-theory of life, the, 29, 30, 102.

Macrogameton, 244.

Mammals, common descent of the, 284; motor apparatus of the, 283.

Manners and morals, 421.

Marriage, development of, 402, 403; evolution of, 427; priestly control of, 428.

Materialism, 82, 451.

Mathematics, 456.

Matrimony, 427, 428.

Matter as attribute of substance, 448.

Mechanical embryology, 103.

Mechanics, 259.

Medicine, development of, 462.

Membranes, cellular, 144, 145, 155, 157, 194.

Memory, 416.

Mental disease, evidential value of, 19.

Metabolism, 28,38, 44, 46, 103, 130, 210, 211, 217; a mechanical process, 259, 260; in the metaphyta, 219-221; in the metazoa, 221, 233; in the protophyta, 217-219; in the protozoa, 219, 220.

Metagenesis, 253.

Metamerism, 167, 168, 281.

Metamorphology, 94.

Metaphysicians disdain physical science, 16.

Metaphysics, nature of, 10, 88, 89.

Metaphyta, 161, 165.

Metaplasm, 106, 129.

Metaplasmosism, 107.

Metasitism 217.

Metazoa, 163.

Micella, 137, 344.

Micrococcus, 201, 202.

Microgameton, 244.

Middle Ages, thought in the, 66, 67.

Mimicry, 421, 422.

Mind, the, 315, 316; a function of the brain, 328-330; evolution of the, 319, 320, 322, 323, 326.

Miracles, 60; in biology, 55; nature of, 54.

Mohl, Hugo, 122.

Molecular structure of the monera, 34, 137; theories of plasm, 342-346.

Molecules, 126, 127.

Monaxonia, 174.

Monera, the, 31-33, 40, 157, 182, 190-209, 342.

Monism, 81, 433-445.

Monobia, 160, 196.

Monoclinism, 247.

Monœcia, 248.

Monogamy, 240.

Morality, 411, 412; a social instinct, 419, 420; conventional, 430; evolution of, 413, 414, 430-432; a form of adaptation, 414.

Morphology, 94, 171.

Morphonta, 149, 152.

Motion in metabolism, 259.

Müller, Johannes, on the nature of life, 49; on sensation, 288.

Muscles, the, 273, 276-279; forms of in lower animals, 278; striated and non-striated, 277.

Muscular cells, 277.

Mutation theory, the, 365, 373.

Myophæna, 269.

Nägeli on evolution, 365; on plasm, 137; on the origin of life, 343, 344, 354, 356; on universality of sensation, 450.

Natural history, 9.

Naturalism, 86, 87.

Necrobiosis, 106, 349.

Neo-Darwinism, 375, 376.

Neo-Lamarckism, 375, 376.

Neovitalism, 48; sceptical and dogmatic, 50.

Neurona, 12, 13, 328.

Nitrobacteria, 201, 215, 218.

Nuclein, 156.

Nucleolus, 140.

Nucleus of the cell, 122, 139, 155.

Nutrition, progress in supply of, 401.

Observation, subjective and objective, 7.

Occultism, 74, 75.

Œcology, 78, 95.

Oken, Lorentz, 79, 80.

Olfactory region, 303.

Ontogeny, 94, 361, 376, 379.

Optimism, 109, 110.

Organella, 35, 130, 159, 163, 191.

Organic chemistry, 37; and inorganic, differences between, 27, 28, 40; meaning of, 37; sensations, 302, 308.

Organism, nature of an, 29, 30, 36.

Organization, nature of, 29; progress of, 338; stages of, 149, 150, 151.

Organs, 159, 163; apparatus of, 164; systems of, 164; of sense and thought, 12.

Osmosis, 39.

Ostwald, as a monist, 38; on enzyma, 46; on growth, 44; on mental energy, 330; system of, 85.

Ovary, 325.

Ovoplasm, 245.

Ovulum, the, 245, 247, 250.

Pædogenesis, 253.

Palavitalism, 48, 49.

Palingenesis, 382.

Pangenesis theory, the, 366.

Panpsychism, 340.

Pantheism, 82.

Paranuclein, 141.

Parasites, 235-238.

Parasitology, 235.

Paratonic movement, 262, 274.

Parthenogenesis, 251, 252.

Passive movements in organisms, 262.

Pasteur disproves spontaneous generation, 350-352.

Paulospores, 244.

Peptones, 45.

Perception of stimuli, 292, 293, 296.

Perigenesis of the plastidules, 136.

Perpetual motion of universe, 258.

Persons, 36, 148, 150, 154, 166, 183.

Pessimism, 109, 110, 111.

Pflüger on origin of life, 345, 346, 356.

Philology, 461.

Philosophy, history of, 81; modern, defects of, 453; nature of, 2, 3, 453, 454.

Phoronomy, 259.

Photo-synthesis, 214, 217.

Phototaxis, 298.

Phronema, the, 14, 15-17; structure of the, 329.

Phroneta, the, 13, 329, 331.

Phronetal cells, 14, 17.

Phylogeny, 94, 361, 376, 379; sources of, 377.

Physicians, liberal views of, 116-118.

Physics, monism of, 455; nature of, 89, 454.

Physiologists, dualism of, 18.

Physiology, 93.

Phytomonera, 193.

Phytoplasm, 213, 217.

Piano theory of the soul, 16.

Pineal gland, the, 16.

Planospores, 244.

Plants, spontaneous movement in, 274, 275.

Plasm, 121, 123, 128-146; chemical constituents of, 125, 126; differentiation of the, 138; molecules of, 136; nature of, 27, 28, 159; structure of, 128, 129, 130-138.

Plasma products, 144.

Plasmodomism, 33, 34, 130, 193, 197, 212, 213, 343, 357.

Plasmogony, 354.

Plasmophaga, 193, 196, 200, 212.

Plasson, 158.

Plassonella, 355, 358.

Plastids, 138, 192.

Plastidules, 136.

Plastin, 141.

Plate on Darwinism, 364.

Platnosphæra, 174.

Plato, dualism of, 436; philosophy of, 66.

Platodes, 225.

Pleuronectides, 178.

Poetry, pedagogical value of, 439.

Poisonous bacteria, 221, 305; fungi, 236.

Polioplasm, 130, 143.

Politics, 467.

Polytomy, 243.

Powder, 31.

Pressure, sense of, 310.

Preyer on the child-soul, 20; on the earth as an organism, 37; on universality of life, 340.

Principle of individuation, 153.

Probionta, 354.

Promorphology, 94, 172.

Protamœba, 206.

Proteids, 126, 127.

Protestants, liberalism among, 73.

Protists, the, 34, 35, 131, 160, 171, 182, 190-209; can endure extreme temperatures, 300; movements of the, 267, 271; science of the, 92, 93; sensitiveness to electricity, 313.

Protoplasm, 32; nature of, 121, 122, 125.

Providence, belief in, 107, 108.

Pseudopodia, 268.

Psychiatry, 19, 329, 463.

Psychogenesis, 21.

Psychology, 461; comparative, 21, 22; modern, errors of, 71; monistic, 322; nature of, 18.

Psycho-monism, 92.

Psychophysics, 330.

Pteridophyta, 162, 220.

Ptomaines, 203.

Purposive movement, 264, 265.

Pyramidal types, 176.

Radiolaria, 41, 156, 172, 181; movement in the, 322.

Ranke, J., on evolution, 322.

Rational sciences, 470.

Reaction, 293.

Realism, 90, 91.

Reason, 316, 317; pure and practical, 317.

Reason and authority, 423.

Redemption, dogma of, 62.

Reflex movement, 262, 263.

Regeneration, organic, 101-105.

Reinke, as vitalist, 51; dualism of, 30; on the monera, 31; on the origin of life, 337; theory of dominants, 264; works of, 80, 81.

Release of energy, 294.

Religion, evolution of, 57-65, 420, 421, 424.

Reproduction a monistic process, 257; by division, 242; nature of, 241.

Respiration, 228-232.

Resurrection, the, 64.

Resurrection plants, 262.

Rhizomonera, 206.

Rhizopods, 129, 192, 193, 219; movement in the, 270.

Rhodocytes, 228.

Rhumbler, L., on the cell-life, 132.

Rhythmic beauty, 185.

Richter, H. E., on life, 339.

Rindfleisch, as vitalist, 51.

Romanes, conversion of, 22, 23.

Romanism, 63, 425, 426.

Sacraments, 425, 426.

Saposites, 234.

Saprobiosis, 349, 350.

Sarcode, 155.

Savage, mind in the, 56, 57, 90, 333, 391, 405, 406, 424; religion of the, 57; sense-life in the, 406, 407; views of the, 390.

Savages, higher, 394; life of the, 392-394; lower, 398; middle, 393.

Schiller, idealism of, 439, 440-442.

Schizpphyta, 201.

Schleiden, 154.

Schleiermacher, 72.

Schopenhauer, as pessimist, 111, 112; on the categorical imperative, 412; on suicide, 114.

Schultze, Max, on the cell, 155.

Schwann, 154.

Science, confusion in, 77; nature of, 4; schools of, 4; work of, 5, 6; value of, 407, 408.

Science and tradition, conflict of, 70, 71.

Secretory movement, 271.

Selection, theory of, 361, 363.

Self-cleavage, 242.

Self-consciousness, beginning of, 323, 324.

Semi-dogmatic sciences, 470.

Senility, causes of, 106.

Sensation and consciousness, 290, 291, 295.

Sensation as attribute of substance, 447, 448; analysis of, 293; common to all bodies, 295, 296, 309; evolution of, 450; in atoms, 83; in plants, 292, 304; nature of, 287-293; neglected by physiologists, 289, 292; of matter, 302; universal, 449.

Sensations in savage and civilized man, 405, 406; organic, 302, 308.

Sense-centres, 13, 329.

Senses, finer development of the, 406.

Sensibility, 287, 288, 293.

Sensitiveness, 293.

Sensorium, the, 14.

Sensualism, 4, 14, 15.

Sentiment and reason, 120.

Sex sense, the, 245.

Sexual beauty, 186.

---- characters, secondary, 251.

---- generation, 244-253.

---- selection, 251.

---- sense, the, 306, 307.

Shame, feeling of, 423.

Sight, evolution of, 24.

Silicon, 40.

Skeletal theory of plasm, 113.

Skeleton, common type of the, 371.

---- the, 278, 279, 283, 284.

Sleep of flowers, 274.

Smell, 303, 304.

Snails, evolution of the, 279; muscles of the, 278.

Sociology, 467.

Soul, the, 315, 324; dualistic idea of the, 15, 16; found in all substance, 397; seat of the, 15-18.

Space, nature of, 70; sense of, 311.

Spallanzani and spontaneous generation, 350.

Spartan selection, 22, 119.

Specialism, dangers of, 92.

Species, nature of the, 204.

Speech, 461.

Sperm-plasm, 245.

Spermatozoon, the, 245; movement of the, 271, 272.

Spinoza, system of, 82; monism of, 445.

Spirilla, 202.

Spiritism, 74, 75,

Spiritualism, 451.

Spontaneous generation, 348; conflict over, 349, 350; older belief in, 349.

Sporangia, 244.

Spores, 244.

Sporozoa, 235.

Sprouts, 36, 148, 151, 154, 165, 183.

State and the individual, the, 409.

States, modern, defects of, 409, 410.

Stationary life in animals, 275.

Stauraxonia, 175.

Stimuli, acoustic, 311; action of, 295; chemical, 301-309; conduction of, 295, 396; electric, 312, 313; gravitational, 309-312; optic, 297-300; thermic, 299-302.

Stock, the, 168, 184.

Strauss, D. F., 72.

Strophogenesis, 254.

Substance, attributes of, 446, 448; eternity, of, 97; the problem of, 2.

Suicide, contradictory views of, 112; occasional justice of, 112, 113, 116.

Sun-dew, action of the, 304.

Supernatural, the, 87, 88.

Superstition, 56.

Sutherland, A., on morality, 392.

Swimming-bladder, the, 231.

Symbiosis, 238.

Symmetry, 171, 172.

Sympathy, 115.

Tailor theory, the, 383.

Tape-worms, 237.

Taste, 302, 303.

Technical science, progress of, 465.

Tectology, 94.

Teleology, 181, 366.

Teleology in movement, 265.

Teleology, mechanical, 362, 363.

Temperature, perception of, 299-301.

Thallophyta, 161, 165.

Thallus, the, 165, 195.

Theology, 468.

Thermotaxis, 301.

Thigmotaxis, 310.

Thought as attribute of substance, 445.

Thought centres, 13, 329.

Time, nature of, 70.

Tissue animals, 163; plants, 162.

Tissues, primary and secondary, 161, 162.

Tocogony, 240.

Touch, sense of, 309; in plants, 300, 310.

Tracheata, the, 231.

Tradition, power of, 423.

Transgressive growth, 42, 44, 240, 241.

Transubstantiation, 426.

Treviranus, 79.

Tropesis, 296, 308.

Trophoplasts, 143.

Truth, nature of, 1, 2, 4.

Tübingen school, the, 72.

Turgescence movements, 274, 275.

Turgor, 273-275.

Types of organic structure, 173-184.

Unequal value of life, 390.

Value of modern life, 408, 409.

Variability in species, 373.

Variation movements, 274.

Veddahs, the, 393.

Vegetal diet, 227.

Vertebrates, mind in the, 328; motor apparatus of the, 283, 284; succession of the, 327.

Verworn, Max. on enzyma, 46; on the nature of life, 28; on the origin of life, 348.

Vibratory movement, 271.

Virchow and evolution, 322; on the aim of science, 5.

Vital force, the, 47-51.

---- movement, 266-286.

Vitalism, 47-51, 459.

Voluntary movement mechanical, 262-264.

War, 400, 409.

Watch compared with organism, 30.

Water-feet, 280.

Water-vessels, 230.

Weismann on immortality, 90-101; on selection, 364; on the structure of plasm, 137.

Will, freedom of the, 263, 265, 286.

Wind-pipe, the, 232.

Woman, improvement in position of, 402.

Zehnder on the origin of life, 344.

Ziegler on instinct, 418.

Zoomonera, 193, 219.

Zooplasm, 213.

THE END

FOOTNOTES:

[1] The English translation met with almost equal success. Nearly one hundred thousand copies of the cheap edition have already been sold.--TRANS.

[2] Further particulars about the relations of the thought-centres to the sense-centres will be found in the tenth chapter of _The Riddle of the Universe_.

[3] English readers who are acquainted with Romanes's posthumous _Thoughts on Religion_ will recognize the justice of this analysis. Romanes speaks expressly of the acceptance of Christianity entailing "the sacrifice of his intellect."--TRANS.

[4] This refers almost entirely to Germany. The reader will remember that, when Lord Kelvin endeavored to make theosophic capital out of this temporary confusion in German science, he was immediately silenced by the leading biologists of this country, Professor E. Ray-Lankester (for zoology), Sir W. T. Thiselton-Dyer (for botany), and Sir J. Burdon-Sanderson (for physiology), who sharply rejected vitalism.--TRANS.

[5] The German word _wunder_ corresponds equally to the English "miracle" and "wonder." It has seemed necessary to translate it "wonder" in the title of the work, but frequently as "miracle" in this chapter.--TRANS.

[6] The English reader may usefully be reminded that Professor Loofs, Haeckel's chief critic, and one of the foremost German theologians, rejects these articles of the Creed no less than Haeckel does. A glance at the pertinent articles in the _Encyclopædia Biblica_ will show how widely theologians now discard these beliefs.--TRANS.

[7] Compare the opinion of the distinguished American psychologist, Münsterberg "Science opposes to any doctrine of individual immortality an unbroken and impregnable barrier" (_Psychology and Life_, p. 85).--TRANS.

[8] A translation of the latest edition of the _Anthropogenie_, with the full number of fresh illustrations (thirty plates and five hundred and twelve wood-cuts), will be issued very shortly by the Rationalist Press Association, under the title of _The Evolution of Man_.

[9] I may remind the English reader that the chosen ecclesiastical champion against Haeckel in this country, the Rev. F. Ballard, made this extraordinary fallacy the very pith of his "scientific" attack on monism.--TRANS.

[10] As already stated, it will presently appear in England with the title, _The Evolution of Man_.--TRANS.

[11] At the moment I translate this, telegrams from Germany announce that, by the emperor's orders, a number of ladies were excluded from the opera for not observing this custom.--TRANS.

[12] The English reader will find in this a reply to the foolish notion which has been circulated that the recent discovery of radioaction and the composition of the atom from electrons has affected Haeckel's position. His monism is completely indifferent to changes in the physicist conception of the nature of matter.--TRANS.

TRANSCRIBER'S NOTES:

--Obvious print and punctuation errors were corrected.

--The large tables at pages 96 and 189 have been splitted into two parts.

--Original work has "CHAPTER I" instead of "CHAPTER VI" at page 121. Corrected.

--Original work does not have "XI" at the beginning of chapter (page 239). Added.