Part I, contains an element of truth.

* * * * *

Some clear idea of the nature of Life itself, must, indeed, form a needful preliminary. We may be sure that a search for the influences determining the maintenance and multiplication of living organisms, cannot be successfully carried out unless we understand what is the peculiar property of a living organism--what is the widest generalization of the phenomena that indicate life. By way of preparation, therefore, for the Theory of Population presently to be developed, we propose devoting a brief space to this prior question.

* * * * *

Employing the term, then, in its usual sense, as applicable only to organisms, Life may be defined as--_the co-ordination of actions_. The growth of a crystal, which is the highest inorganic process we are acquainted with, involves but one action--that of accretion. The growth of a cell, which is the lowest organic process, involves two actions--accretion and disintegration--repair and waste--assimilation and oxidation. Wholly deprive a cell of oxygen, and it becomes inert--ceases to manifest vital phenomena; or, as we say, dies. Give it no matter to assimilate, and it wastes away and disappears, from continual oxidation. Evidently, then, it is in the balance of these two actions that the life consists. It is not in the assimilation alone; for the crystal assimilates: neither is it in the oxidation alone; for oxidation is common to inorganic matter: but it is in the joint maintenance of these--the _co-ordination_ of them. So long as the two go on together, life continues: suspend either of them, and the result is--death.

The attribute which thus distinguishes the lowest organic from the highest inorganic bodies, similarly distinguishes the higher organisms from the lower ones. It is in the greater complexity of the co-ordination--that is, in the greater number and variety of the co-ordinated actions--that every advance in the scale of being essentially consists. And whether we regard the numerous vital processes carried on in a creature of complex structure as so many additional processes, or whether, more philosophically, we regard them as subdivisions of the two fundamental ones--oxidation and accretion--the co-ordination of them is still the life. Thus turning to what is physiologically classified as the _vegetative system_, we see that stomach, lungs, heart, liver, skin, and the rest, must work in concert. If one of them does too much or too little--that is, if the co-ordination be imperfect--the life is disturbed; and if one of them ceases to act--that is, if the co-ordination be destroyed--the life is destroyed. So likewise is it with the _animal system_, which indirectly assists in co-ordinating the actions of the viscera by supplying food and oxygen. Its component parts, the limbs, senses, and instruments of attack or defence must perform their several offices in proper sequence; and further, must conjointly minister to the periodic demands of the viscera, that these may in turn supply blood. How completely the several attributes of animal life come within the definition, we shall best see on going through them _seriatim_.

Thus _Strength_ results from the co-ordination of actions; for it is produced by the simultaneous contraction of many muscles and many fibres of each muscle; and the strength is great in proportion to the number of these acting together--that is, in proportion to the co-ordination. _Swiftness_ also, depending partly on strength, but requiring also the rapid alternation of movements, equally comes under the expression; seeing that, other things equal, the more quickly sequent actions can be made to follow each other, the more completely are they co-ordinated. So, too, is it with _Agility_; the power of a chamois to spring with safety from crag to crag implies accurate co-ordination in the movements of many different muscles, and a due subordination of them all to the perceptions. The definition similarly includes _Instinct_, which consists in the uniform succession of certain actions or series of actions after certain sensations or groups of sensations; and that which surprises us in instinct is the accuracy with which these compound actions respond to these compound sensations; that is--the completeness of their co-ordination. Thus, likewise, is it with _Intelligence_, even in its highest manifestations. That which we call rationality is the power to combine, or co-ordinate a great number and a great variety of complex actions for the achievement of a desired result. The husbandman has in the course of years, by drainage and manuring, to bring his ground into a fertile state; in the autumn he must plough, harrow, and sow, for his next year's crop; must subsequently hoe and weed, keep out cattle, and scare away birds; when harvest comes, must adapt the mode and time of getting in his produce to the weather and the labour market; he must afterwards decide when, and where, and how to sell to the best advantage; and must do all this that he may get food and clothing for his family. By properly coordinating these various processes (each of which involves many others)--by choosing right modes, right times, right quantities, right qualities, and performing his acts in right order, he attains his end. But if he have done too little of this, or too much of that; or have done one thing when he should have done another--if his proceedings have been badly co-ordinated--that is, if he have lacked intelligence--he fails.

We find, then, that _the co-ordination of actions_ is a definition of Life, which includes alike its highest and its lowest manifestations; and not only so, but expresses likewise the degree of Life, seeing that the Life is high in proportion as the co-ordination is great. Proceeding upwards, from the simplest organic cell in which there are but two interdependent actions, on through the group in which many such cells are acting in concert, on through the higher group in which some of these cells assume mainly the respiratory and others the assimilative function--proceeding still higher to organisms in which these two functions are subdivided into many others, and in which some cells begin to act together as contractile fibres; next to organisms in which the visceral division of labour is carried yet further, and in which many contractile fibres act together as muscles--ascending again to creatures that combine the movements of several limbs and many bones and muscles in one action; and further, to creatures in which complex impressions are followed by the complex acts we term instinctive--and arriving finally at man, in whom not only are the separate acts complex, but who achieves his ends by combining together an immense number and variety of acts often extending through years--we see that the progress is uniformly towards greater co-ordination of actions. Moreover, this co-ordination of actions unconsciously constitutes the essence of our common notion of life; for we shall find, on inquiry, that when we infer the death of an animal, which does not move on being touched, we infer it because we miss the usual co-ordination of a sensation and a motion: and we shall also find, that the test by which we habitually rank creatures high or low in the scale of vitality is the degree of co-ordination their actions exhibit.

* * * * *

There remains but to notice the objection which possibly may be raised, that the co-ordination of actions is not life, but the ability to maintain life. Lack of space forbids going into this at length. It must suffice to say, that life and the ability to maintain life will be found the same. We perpetually expend the vitality we have that we may continue our vitality. Our power to breathe a minute hence depends upon our breathing now. We must digest during this week that we may have strength to digest next. That we may get more food, we must use the force which the food we have eaten gives us. Everywhere vigorous life is the strength, activity, and sagacity whereby life is maintained; and equally in descending the scale of being, or in watching the decline of an invalid, we see that the ebbing away of life is the ebbing away of the ability to preserve life.[62]

[Only on now coming to re-read the definition of Life enunciated at the commencement of this essay with the arguments used in justification of it, does it occur to me that its essential thought ought to have been incorporated in the definition of Life given in Part I. The idea of co-ordination is there implied in the idea of correspondence, but the idea of co-ordination is so cardinal a one that it should be expressed not by implication but overtly. It is too late to make the required amendment in the proper place, for the first part of this work is already stereotyped and printed. Being unable to do better I make the amendment here. The formula as completed will run:--The definite combination of heterogeneous changes, both simultaneous and successful, _co-ordinated into_ correspondence with external co-existences and sequences.]

* * * * *

Ending here this preliminary dissertation, let us now proceed to our special subject.

§ 1. On contemplating its general circumstances, we perceive that any race of organisms is subject to two sets of conflicting influences. On the one hand by natural death, by enemies, by lack of food, by atmospheric changes, &c., it is constantly being destroyed. On the other hand, partly by the strength, swiftness and sagacity of its members, and partly by their fertility, it is constantly being maintained. These conflicting sets of influences may be conveniently generalized as--the forces destructive of race, and the forces preservative of race.

§ 2. Whilst any race continues to exist, the forces destructive of it and the forces preservative of it must perpetually tend towards equilibrium. If the forces destructive of it decrease, the race must gradually become more numerous, until, either from lack of food or from increase of enemies, the destroying forces again balance the preserving forces. If, reversely, the forces destructive of it increase, then the race must diminish, until, either from its food becoming relatively more abundant, or from its enemies dying of hunger, the destroying forces sink to the level of the preserving forces. Should the destroying forces be of a kind that cannot be thus met (as great change of climate), the race, by becoming extinct, is removed out of the category. Hence this is necessarily the _law of maintenance_ of all races; seeing that when they cease to conform to it they cease to be.

Now the forces preservative of race are two--ability in each member of the race to preserve itself, and ability to produce other members--power to maintain individual life, and power to propagate the species. These must vary inversely. When, from lowness of organization, the ability to contend with external dangers is small, there must be great fertility to compensate for the consequent mortality; otherwise the race must die out. When, on the contrary, high endowments give much capacity of self-preservation, there needs a correspondingly low degree of fertility. Given the dangers to be met as a constant quantity; then, as the ability of any species to meet them must be a constant quantity too, and as this is made up of the two factors--power to maintain individual life and power to multiply--these cannot do other than vary inversely.

§ 3. To show that observed phenomena harmonise with this _à priori_ principle seems scarcely needful But, though axiomatic in its character, and therefore incapable of being rendered more certain, yet illustrations of the conformity to it which nature everywhere exhibits, will facilitate the general apprehension of it.

In the vegetable kingdom we find that the species consisting of simple cells, exhibit the highest reproductive power. The yeast fungus, which in a few hours propagates itself throughout a large mass of wort, offers a familiar example of the extreme rapidity with which these lowly organisms multiply. In the _Protococcus nivalis_, a microscopic plant which in the course of a night reddens many square miles of snow, we have a like example; as also in the minute _Algæ_, which colour the waters of stagnant pools. The sudden appearance of green films on damp decaying surfaces, the spread of mould over stale food, and the rapid destruction of crops by mildew, afford further instances. If we ascend a step to plants of appreciable size, we still find that in proportion as the organization is low the fertility is great. Thus of the common puff-ball, which is little more than a mere aggregation of cells, Fries says, "in a single individual of _Reticularia maxima_, I have counted (calculated?) 10,000,000 sporules." From this point upwards, increase of bulk and greater complexity of structure are still accompanied by diminished reproductive power; instance the _Macrocystis pyrifera_, a gigantic sea-weed, which sometimes attains a length of 1500 feet, of which Carpenter remarks, "This development of the nutritive surface takes place at the expense of the fructifying apparatus, which is here quite subordinate."[63] And when we arrive at the highly-organized exogenous trees, we find that not only are they many years before beginning to bear with any abundance, but that even then they produce, at the outside, but a few thousand seeds in a twelvemonth. During its centuries of existence, an oak does not develop as many acorns as a fungus does spores in a single night.

Still more clearly is this truth illustrated throughout the animal kingdom. Though not so great as the fertility of the Protophyta, which, as Prof. Henslow says, in some cases passes comprehension, the fertility of the Protozoa is yet almost beyond belief. In the polygastric animalcules spontaneous fission takes place so rapidly that "it has been calculated by Prof. Ehrenberg that no fewer than 268 millions might be produced in a month from a single _Paramecium_;"[64] and even this astonishing rate of increase is far exceeded in another species, one individual of which, "only to be perceived by means of a high magnifying power, is calculated to generate 170 billions in four days."[65] Amongst the larger organisms exhibiting this lowest mode of reproduction under a modified form--that of gemmation--we see that, though not nearly so rapid as in the Infusoria, the rate of multiplication is still extremely high. This fact is well illustrated by the polypes; and in the apparent suddenness with which whole districts are blighted by the Aphis (multiplying by internal gemmation), we have a familiar instance of the startling results which the parthenogenetic process can achieve. Where reproduction becomes occasional instead of continuous, as it does amongst higher creatures, the fertility equally bears an inverse ratio to the development. "The queen ant of the African _Termites_ lays 80,000 eggs in twenty-four hours; and the common hairworm (_Gordius_) as many as 8,000,000 in less than one day."[66] Amongst the _Vertebrata_ the lowest are still the most prolific. "It has been calculated," says Carpenter, "that above a million of eggs are produced at once by a single codfish."[67] In the strong and sagacious shark comparatively few are found. Still less fertile are the higher reptiles. And amongst the Mammalia, beginning with small Rodents, which quickly reach maturity, produce large litters, and several litters in the year; advancing step by step to the higher mammals, some of which are long in attaining the reproductive age, others of which produce but one litter in a year, others but one young one at a time, others who unite these peculiarities; and ending with the elephant and man, the least prolific of all, we find that throughout this class, as throughout the rest, ability to multiply decreases as ability to maintain individual life increases.

§ 4. The _à priori_ principle thus exemplified has an obverse of a like axiomatic character. We have seen that for the continuance of any race of organisms it is needful that the power of self-preservation and the power of reproduction should vary inversely.

We shall now see that, quite irrespective of such an end to be subserved, these powers could not do otherwise than vary inversely. In the nature of things species can subsist only by conforming to this law; and equally in the nature of things they cannot help conforming to it.

Reproduction, under all its forms, may be described as the separation of portions of a parent plant or animal for the purpose of forming other plants or animals. Whether it be by spontaneous fission, by gemmation, or by gemmules; whether the detached products be bulbels, spores or seeds, ovisacs, ova or spermatozoa; or however the process of multiplication be modified, it essentially consists in the throwing off of parts of adult organisms for the purpose of making new organisms. On the other hand, self preservation is fundamentally a maintenance of the organism in undiminished bulk. Amongst the lowest forms of life, aggregation of tissue is the only mode in which the self-preserving power is shown. Even in the highest, sustaining the body in its integrity is that in which self-preservation most truly consists--is the end which the widest intelligence is indirectly made to subserve. Whilst, on the one side, it cannot be denied that the increase of tissue constituting growth is self-preservation both in essence and in result; neither can it, on the other side, be denied that a diminution of tissue, either from injury, disease, or old age, is in both essence and result the reverse.

Hence the maintenance of the individual and the propagation of the race being respectively aggregative and separative, _necessarily_ vary inversely. Every generative product is a deduction from the parental life; and, as already pointed out, to diminish life is to diminish the ability to preserve life. The portion thrown off is organised matter; vital force has been expended in the organisation of it, and in the assimilation of its component elements; which vital force, had no such portion been made and thrown off, _would have been available for the preservation of the parent_.

Neither of these forces, therefore, can increase, save at the expense of the other. The one draws in and incorporates new material; the other throws off material previously incorporated. The one adds to; the other takes from. Using a convenient expression for describing the facts (though one that must not be construed into an hypothesis), we may say that the force which builds up and repairs the individual is an attractive force, whilst that which throws off germs is a repulsive force. But whatever may turn out to be the true nature of the two processes, it is clear that they are mutually destructive; or, stating the proposition in its briefest form--Individuation and Reproduction are antagonistic.

Again, illustrating the abstract by reference to the concrete, let us now trace throughout the organic world the various phases of this antagonism.

§ 5. All the lowest animal and vegetable forms--_Protozoa_ and _Protophyta_--consist essentially of a single cell containing fluid, and having usually a solid nucleus. This is true of the Infusoria, the simplest Entozoa, and the microscopic Algæ and Fungi. The organisms so constituted uniformly multiply by spontaneous fission. The nucleus, originally spherical, becomes elongated, then constricted across its smallest diameter, and ultimately separates, when "its divisions," says Prof. Owen, describing the process in the Infusoria, "seem to repel each other to positions equidistant from each other, and from the pole or end of the body to which they are nearest. The influence of these distinct centres of assimilation is to divert the flow of the plasmatic fluid from a common course through the body of the polygastrian to two special courses about those centres. So much of the primary developmental process is renewed, as leads to the insulation of the sphere of the influence of each assimilative centre from that of the other by the progressive formation of a double party wall of integument, attended by progressive separation of one party wall from the other, and by concomitant constriction of the body of the polygastrian, until the vibratile action of the superficial cilia of each separating moiety severs the narrowed neck of union, and they become two distinct individuals."[68] Similar in its general view is Dr. Carpenter's description of the multiplication of vegetable cells, which he says divide, "in virtue, it may be surmised, of a sort of mutual repulsion between the two halves of the endochrome (coloured cell-contents) which leads to their spontaneous separation."[69] Under a modified form of this process, the cell-contents, instead of undergoing bisection, divide into numerous parts, each of which ultimately becomes a separate individual. In some of the Algæ "a whole brood of young cells may thus be at once generated in the cavity of the parent-cell, which subsequently bursts and sets them free."[70] The _Achlya prolifera_ multiplies after this fashion. Amongst the Fungi, too, the same mode of increase is exemplified by the _Protococcus nivalis_. And "it would appear that certain Infusoria, especially the _Kolpodinæ_, propagate by the breaking-up of their own mass into reproductive particles."[71]

Now in this fissiparous mode of multiplication, which "is amazingly productive, and indeed surpasses in fertility any other with which we are acquainted,"[72] we see most clearly the antagonism between individuation and reproduction. We see that the reproductive process involves destruction of the individual; for in becoming two, the parent fungus or polygastrian must be held to lose its own proper existence; and when it breaks up into a numerous progeny, does so still more completely. Moreover, this rapid mode of multiplication not only destroys the individuals in whom it takes place, but also involves that their individualities, whilst they continue, shall be of the lowest kind. For assume a protozoon to be growing by imbibition at a given rate, and it follows that the oftener it divides the smaller must be the size it attains to; that is, the smaller the development of its individuality. And a further manifestation of the same truth is seen in the fact that the more frequent the spontaneous fission the shorter the existence of each individual. So that alike by preventing anything beyond a microscopic bulk being attained, by preventing the continuance of this in its integrity beyond a few hours, and by being fatal when it occurs, this most active mode of reproduction shows the strongest antagonism to individual life.

§ 6. Whether or not we regard reproduction as resulting from a repulsive force (and, as seen above, both Owen and Carpenter lean to some such view), and whether or not we consider the formation of the individual as due to the reverse of this--an attractive force--we cannot, on studying the phenomena, help admitting that two opposite activities thus generalized are at work; we cannot help admitting that the aggregative and separative tendencies do in each case determine the respective developments of the individual and the race. On ascending one degree in the scale of organic life, we shall find this truth clearly exemplified.

For if these single-celled organisms which multiply so rapidly be supposed to lose some of their separative tendency, what must be the result? They now not only divide frequently, but the divided portions fly apart. How, then, will a diminution of this separative tendency first show itself? May we not expect that it will show itself in the divided portions _not_ flying apart, but remaining near each other, and forming a group? This we find in nature to be the first step in advance. The lowest compound organisms are "_simple aggregations of vesicles without any definite arrangement, sometimes united, but capable of existing separately_."[73] In these cases, "every component cell of the aggregate mass that springs from a single germ, being capable of existing independently of the rest, may be regarded as a distinct individual."[74] The several stages of this aggregation are very clearly seen in both the animal and vegetable kingdoms. In the _Hæmatococcus binalis_, the plant producing the reddish slime seen on damp surfaces, not only does each of the cells retain its original sphericity, but each is separated from its neighbour by a wide interval filled with mucus; so that it is only as being diffused through a mass of mucus common to them all, that these cells can be held to constitute one individual. We find, too, that "the component cells, even in the highest Algæ, are generally separated from each other by a large quantity of mucilaginous intercellular substance."[75] And, again, the tissue of the simpler Lichens, "in consequence of the very slight adhesion of its component cells, is said to be pulverulent."[76] Similarly the Protozoa, by their feeble union, constitute the organisms next above them. Amongst the Polygastrica there are many cases "in which the individuals produced by fission or gemmation do not become completely detached from each other."[77] The _Ophrydium_, for instance, "exists under the form of a motionless jelly-like mass ... made up of millions of distinct and similar individuals imbedded in a gelatinous connecting substance;"[78] and again, the _Uvella_, or "grape monad," consists of a cluster "which strongly resembles a transparent mulberry rolling itself across the field of view by the ciliary action of its component individuals."[79] The parenchyma of the Sponge, too, is made up of cells "each of which has the character of a distinct animalcule, having a certain power of spontaneous motion, obtaining and assimilating its own food, and altogether living _by_ and _for_ itself;" and so small is the cohesion of these individual cells, that the tissue they constitute "drains away when the mass is removed from the water, like white of egg."[80]

Of course in proportion as the aggregate tendency leading to the formation of these groups of monads is strong, we may expect that, other things equal, the groups will be large. Proceeding upwards from the yeast fungus, whose cells hold together in groups of four, five, and six,[81] there must be found in each species of these composite organisms a size of group determined by the strength of the aggregative tendency in that species. Hence we may expect that, when this limit is passed, the group no longer remains united, but divides. Such we find to be the fact. These groups of cells undergo the same process that the cells themselves do. They increase up to a certain point, and then multiply either by simple spontaneous fission or by that modification of it called gemmation. The _Volvox globator_, which is made up of a number of monads associated together in the form of a hollow sphere, develops within itself a number of smaller spheres similarly constituted; and after these, swimming freely in its interior, have reached a certain size, the parent group of animalcules bursts and sets the interior groups free. And here we may observe how this compound individuality of the Volvox is destroyed in the act of reproduction as the simple individuality of the monad is. Again, in the higher forms of grouped cells, where something like organisation begins to show itself, the aggregations are not only larger, but the separative process, now carried on by the method of gemmation, no longer wholly destroys the individual. And in fact, this gemmation may be regarded as the form which spontaneous fission must assume in ceasing to be fatal; seeing that gemmation essentially consists in the separation, not into halves, but into a larger part and a smaller part; the larger part continuing to represent the original individual. Thus in the common _Hydra_ or fresh-water polype, "little bud-like processes are developed from the external surface, which are soon observed to resemble the parent in character, possessing a digestive sac, mouth, and tentacula; for a long time, however, their cavity is connected with that of the parent; but at last the communication is cut off, and the young polype quits its attachment, and goes in quest of its own maintenance."[82]

§ 7. Progress from these forms of organisation to still higher forms is similarly characterized by increase of the aggregative tendency or diminution of the separative, and similarly exhibits the necessary antagonism between the development of the individual and the increase of the race. That process of grouping which constitutes the first step towards the production of complex organisms, we shall now find repeated in the formation of series of groups. Just as a diminution of the separative tendency is shown in the aggregation of divided monads, so is a further diminution of it shown in the aggregation of the divided groups of monads. The first instance that occurs is afforded by the compound polypes. "Some of the simpler forms of the composite _Hydroida_," says Carpenter, "may be likened to a _Hydra_, whose gemmæ, instead of becoming detached, remain permanently connected with the parent; and as these in their turn may develop gemmæ from their own bodies, a structure of more or less arborescent character may be produced."[83] A similar species of combination is observable amongst the _Bryozoa_, and the compound _Tunicata_. Every degree of union may be found amongst these associated organisms; from the one extreme in which the individuals can exist as well apart as together, to the other extreme in which the individuals are lost in the general mass. Whilst each _Bryozoon_ is tolerably independent of its neighbour, "in the compound _Hydroida_, the lives of the polypes are subordinate to that of the polypdom."[84] Of the _Salpidæ_ and _Pyrosomidæ_, Carpenter says:--"Although closely attached to one another, these associated animals are capable of being separated by a smart shock applied to the sides of the vessel in which they are swimming.... In other species, however, the separate animals are imbedded in a gelatinous mass," and in one kind "there is an absolute union between the vascular systems of the different individuals."[85]

In the same manner that with a given aggregative tendency there is a limit to the size of groups, so is there a similarly-determined limit to the size of series of groups; and that spontaneous fission which we have seen in cells and groups of cells we here find repeated. In the lower _Annelida_, for example, "after the number of segments in the body has been greatly multiplied by gemmation, a separation of those of the posterior portion begins to take place; a constriction forms itself about the beginning of the posterior third of the body, in front of which the alimentary canal undergoes a dilatation, whilst on the segment behind it a proboscis and eyes are developed, so as to form the head of the young animal which is to be budded off; and in due time, by the narrowing of the constriction, a complete separation is effected."[86] Not unfrequently in the _Nais_ this process is repeated in the young one before it becomes independent of the parent. The higher _Annelida_ are distinguished by the greater number of segments held in continuity; an obvious result of comparatively infrequent fission. In the class _Myriapoda_, which stands next above, "there is no known instance of multiplication by fission."[87] Yet even here the law may be traced both in the number and structure of the segments. The length of the body is still increased after birth "by gemmation from (or partial fission of) the penultimate segment." The lower members of the class are distinguished from the higher by the greater extent to which this gemmation is carried. Moreover, the growing aggregative tendency is seen in the fact, that each segment of the Julus "is formed by the coalescence of two original segments,"[88] whilst in the _Scolopendridæ_, which are the highest of this class, "the head, according to Mr. Newport, is composed of eight segments, which are often consolidated into one piece;"[89] both of which phenomena may be understood as arrests of that process of fission, which, if allowed to go a little further, would have produced distinct segments; and, if allowed to go further still, would have separated these segments into groups.

§ 8. Remarking, first, how gradually this mode of multiplication disappears--how there are some creatures that spontaneously divide or not according to circumstances; others that divide when in danger (the several parts being capable of growing into complete individuals); others which, though not self-dividing, can live on in each half if artificially divided; and others in which only one of the divided halves can live--how, again, in the Crustaceans the power is limited to the reproduction of lost limbs; how there are certain reptiles that can re-supply a lost tail, but only imperfectly; and how amongst the higher _Vertebrata_ the ability to repair small injuries is all that remains--remarking thus much, let us now, by way of preparation for what is to follow, consider the significance of the foregoing facts taken in connection with the definition of Life awhile since given.

This spontaneous fission, which we have seen to be, in all cases, more or less destructive of individual life, is simply a cessation in the co-ordination of actions. From the single cell, the halves of whose nucleus, instead of continuing to act together, begin to repel each other, fly apart, establish distinct centres of assimilation, and finally cause the cell to divide; up to the Annelidan, whose string of segments separates, after reaching a certain length; we everywhere see the phenomenon to be fundamentally this. The tendency to separate is the tendency not to act together, probably arising from inability to act together any longer; and the process of separation is the process of ceasing to act together. How truly non-co-ordination is the essence of the matter will be seen on observing that fission takes place more or less rapidly, according as the co-ordinating apparatus is less or more developed. Thus, "the capability of spontaneous division is one of the most distinctive attributes of the acrite type of structure;"[90] the acrite type of structure being that in which the neurine or nervous matter is supposed to be diffused through the tissues in a molecular state, and in which, therefore, there exists no distinct nervous or co-ordinating system. From this point upwards the gradual disappearance of spontaneous fission is clearly related to the gradual appearance of nerves and ganglia--a fact well exemplified by the several grades of _Annelida_ and _Myriapoda_. And when we remember that in the embryotic development of these classes, the nervous system does not make its appearance until after the rest of the organism has made great progress, we may even suspect that that coalescence of segments characteristic of the _Myriapoda_, exhibits the co-ordinating power of the rapidly-growing nervous system overtaking and arresting the separative tendency; and doing this most where it (the nervous system) is most developed, namely, in the head.

And here let us remark, in passing, how, from this point of view, we still more clearly discern the antagonism of individuation and reproduction. We before saw that the propagation of the race is at the expense of the individual: in the above facts we may contemplate the obverse of this--may see that the formation of the individual is at the expense of the race. This combination of parts that are tending to separate and become distinct beings--this union of many incipient minor individualities into one large individuality--is an arrest of reproduction--a diminution in the number produced. Either these units may part and lead independent lives, or they may remain together and have their actions co-ordinated. Either they may, by their diffusion, form a small, simple, and prolific race, or, by their aggregation, a large, complex, and infertile one. But manifestly the aggregation involves the infertility; and the fertility involves the smallness.

§ 9. The ability to multiply by spontaneous fission, and the ability to maintain individual life, are opposed in yet another mode. It is not in respect of size only, but still more in respect of structure, that the antagonism exists.

Higher organisms are distinguished from lower ones partly by bulk, and partly by complexity. This complexity essentially consists in the mutual dependence of numerous different organs, each subserving the lives of the rest, and each living by the help of the rest. Instead of being made up of many like parts, performing like functions, as the Crinoid, the Star-fish, or the Millipede, a vertebrate animal is made up of many unlike parts, performing unlike functions. From that initial form of a compound organism, in which a number of minor individuals are simply grouped together, we may, more or less distinctly, trace not only the increasing closeness of their union, and the gradual disappearance of their individualities in that of the mass, but the gradual assumption by them of special duties. And this "physiological division of labour," as it has been termed, has the same effect as the division of labour amongst men. As the preservation of a number of persons is better secured when, uniting into a society, they severally undertake different kinds of work, than when they are separate and each performs for himself every kind of work; so the preservation of a congeries of parts, which, combining into one organism, respectively assume nutrition, respiration, circulation, locomotion, as separate functions, is better secured than when those parts are independent, and each fulfils for itself all these functions.

But the condition under which this increased ability to maintain life becomes possible is, that the parts shall cease to separate. While they are perpetually separating, it is clear that they cannot assume mutually subservient duties. And it is further clear that the more the tendency to separate diminishes, that is, the larger the groups that remain connected, _the more minutely and perfectly can that subdivision of functions which we call organization be carried out_.

Thus we see that in its most active form the ability to multiply is antagonistic to the ability to maintain individual life, not only as preventing increase of bulk, but also as preventing organization--not only as preventing homogeneous co-ordination, but as preventing heterogeneous co-ordination.

§ 10. To establish the unbroken continuity of this law of fertility, it will be needful, before tracing its results amongst the higher animals, to explain in what manner spontaneous fission is now understood, and what the cessation of it essentially means. Originally, naturalists supposed that creatures which multiply by self-division, under any of its several forms, continue so to multiply perpetually. In many cases, however, it has latterly been shown that they do not do this; and it is now becoming a received opinion that they do not, and cannot, do this, in any case. A fertilised germ appears here, as amongst higher organisms, to be the point of departure; and that constant formation of new tissue implied in the production of a great number of individuals by fission, seems gradually to exhaust the germinal capacity in the same way that the constant formation of new tissue, during the development of a single mammal, exhausts it. The phenomena classified by Steenstrup as "Alternate Generation," and since generalised by Professor Owen in his work "On Parthenogenesis," illustrate this. The egg of a _Medusa_ (jellyfish) develops into a polypoid animal called the _Strobila_. This _Strobila_ lives as the polype does, and, like it, multiplies rapidly by gemmation. After a great number of individuals has been thus produced, and when, as we must suppose, the germinal capacity is approaching exhaustion, each _Strobila_ begins to exhibit a series of constrictions, giving it some resemblance to a rouleau of coin or a pile of saucers. These constrictions deepen; the segments gradually develop tentacula; the terminal segment finally separates itself, and swims away in the form of a young _Medusa_; the other segments, in succession, do the same; and from the eggs which these _Medusæ_ produce, other like series of polypoid animals, multiplying by gemmation, originate. In the compound Polypes, in the _Tunicata_, in the _Trematoda_, and in the Aphis, we find repeated, under various modifications, the same phenomenon.

Understanding then, this lowest and most rapid mode of multiplication to consist essentially in the production of a great number of individuals from a single germ--perceiving, further, that diminished activity of this mode of multiplication consists essentially in the aggregation of the germ-product into larger masses--and seeing, lastly, that the disappearance of this mode of multiplication consists essentially in the aggregation of the germ-product into _one_ mass--we shall be in a position to comprehend, amongst the higher animals, that new aspect of the law, under which increased individuation still involves diminished reproduction. Progressing from those lowest forms of life in which a single ovum originates countless organisms, through the successive stages in which the number of organisms so originated becomes smaller and smaller; and finally arriving at a stage in which one ovum produces but one organism; we have now, in our further ascent, to observe the modified mode in which this same necessary antagonism between the ability to multiply, and the ability to preserve individual life, is exhibited.

§ 11. Throughout both the animal and vegetable kingdoms, generation is effected "by the union of the contents of a 'sperm-cell' with those of a 'germ-cell;' the latter being that from within which the embryo is evolved, whilst the former supplies some material or influence necessary to its evolution."[91] Amongst the lowest vegetable organisms, as in the _Desmideæ_, the _Diatomaceæ_, and other families of the inferior _Algæ_, those cells do not appreciably differ; and the application to them of the terms "sperm-cell" and "germ-cell" is hypothetical. From this point upwards, however, distinctions become visible. As we advance to higher and higher types of structure, marked differences arise in the character of these cells, in the organs evolving them, and in the position of these organs, which are finally located in separate sexes. Doubtless a separation in the _functions_ of "sperm-cell" and "germ-cell" has simultaneously arisen. That change from homogeneity of function to heterogeneity of function which essentially constitutes progress in organization may be assumed to take place here also; and, indeed, it is probable that the distinction gradually established between these cells, in origin and appearance, is merely significant of, and consequent upon, the distinction that has arisen between them in constitution and office. Let us now inquire in what this distinction consists.

If the foundation of every new organism be laid by the combination of two elements, we may reasonably suspect that these two elements are typical of some two fundamental divisions of which the new organism is to consist. As nothing in nature is without meaning and purpose, we may be sure that the universality of this binary origin, signifies the universality of a binary structure. The simplest and broadest division of which an organism is capable must be that signified. What, then, must this division be?

The proposed definition of organic life supplies an answer. If organic life be the co-ordination of actions, then an organism may be primarily divided into parts whose actions are co-ordinated, and parts which co-ordinate them--organs which are made to work in concert, and the apparatus which makes them so work--or, in other words, the assimilative, vascular, excretory, and muscular systems on the one hand, and the nervous system on the other. The justness of this classification will become further apparent, when it is remembered that by the nervous system alone is the individuality established. By it all parts are made one in purpose, instead of separate; by it the organism is rendered a conscious whole--is enabled to recognise its own extent and limits; and by it are all injuries notified, repairs directed, and the general conservation secured. The more the nervous system is developed, the more reciprocally subservient do the components of the body become--the less can they bear separating. And that which thus individuates many parts into one whole, must be considered as more broadly distinguished from the parts individuated, than any of these parts from each other. Further evidence in support of this position may be drawn from the fact, that as we ascend in the scale of animal life, that is, as the co-ordination of actions becomes greater, we find the co-ordinating or nervous system becoming more and more definitely separated from the rest; and in the vertebrate or highest type of structure we find the division above insisted on distinctly marked. The co-ordinating parts and the parts co-ordinated are placed on opposite sides of the vertebral column. With the exception of a few ganglia, the whole of the nervous masses are contained within the neural arches of the vertebræ; whilst all the viscera and limbs are contained within, or appended to, the hæmal arches--the terms neural and hæmal having, indeed, been chosen to express this fundamental division.

If, then, there be truth in the assumption that the two elements, which, by their union, give origin to a new organism, typify the two essential constituents of such new organism, we must infer that the sperm-cell and germ-cell respectively consist of co-ordinating matter and matter to be co-ordinated--neurine and nutriment. That apparent identity of sperm-cell and germ-cell seen in the lowest forms of life may thus be understood as significant to the fact that no extended co-ordination of actions exists in the generative product--each cell being a separate individual; and the dissimilarity seen in higher organic types may, conversely, be understood as expressive of, and consequent upon, the increasing degree of co-ordination exhibited.[92]

That the sperm-cell and germ-cell are thus contrasted in nature and function may further be suspected on considering the distinctive characteristics of the sexes. Of the two elements they respectively contribute to the formation of a fertile germ, it may be reasonably supposed that each furnishes that which it possesses in greatest abundance and can best spare. Well, in the greater size of the nervous centres in the male, as well as in the fact that during famines men succumb sooner than women, we see that in the male the co-ordinating system is relatively predominant. From the same evidence, as well as from the greater abundance of the cellular and adipose tissues in women, we may infer that the nutritive system predominates in the female.[93] Here, then, is additional support for the hypothesis that the sperm-cell, which is supplied by the male, contains co-ordinating matter, and the germ-cell, which is supplied by the female, contains matter to be co-ordinated.

The same inference may, again, be drawn from a general view of the maternal function. For if, as we see, it is the office of the mother to afford milk to the infant, and during a previous period to afford blood to the foetus, it becomes probable that during a yet earlier stage it is still the function to supply nutriment, though in another form. Indeed when, ascending gradually the scale of animal life, we perceive that this supplying of milk, and before that of blood, is simply a continuation of the previous process, we may be sure that, with Nature's usual consistency, this process is essentially one from the beginning.

Quite in harmony with this hypothesis concerning the respective natures of the sperm-cell and germ-cell is a remark of Carpenter's on the same point:--

"Looking," he says, "to the very equal mode in which the characters of the two parents are mingled in _hybrid_ offspring, and to the certainty that the _material_ conditions which determine the development of the germ are almost exclusively female, it would seem probable that the _dynamical_ conditions are, in great part, furnished by the male."[94]

§ 12. Could nothing but the foregoing indirect evidence be adduced in proof of the proposition that the spermatozoon is essentially a neural element, and the ovum essentially a hæmal element, we should scarcely claim for it anything more than plausibility. On finding, however, that this indirect evidence is merely introductory to evidence of a quite direct nature, its significance will become apparent. Adding to their weight taken separately the force of their mutual confirmation, these two series of proofs will be seen to give the hypothesis a high degree of probability. The direct evidence now to be considered is of several kinds.

On referring to the description of the process of multiplication in monads, quoted some pages back (§ 5), from Professor Owen, the reader will perceive that it is by the pellucid nucleus that the growth and reproduction of these single-celled creatures are regulated. The nucleus controls the circulation of the plasmatic fluid; the fission of the nucleus is the first step towards the formation of another cell; each half of the divided nucleus establishes round itself an independent current; and, apparently, it is by the repulsion of the nuclei that the separation into two individuals is finally effected. All which facts, when generalised, imply that the nucleus is the governing or _co-ordinating_ part. Now, Professor Owen subsequently points out that the matter of the sperm-cell performs in the fertilised germ-cell just this same function which the nucleus performs in a single-celled animal. We find the absorption by a germ-cell of the contents of a sperm-cell "followed by the appearance of a pellucid nucleus in the centre of the opaque and altered germ-cell; we further see its successive fissions governed by the preliminary division of the pellucid centre;" and, led by these and other facts, Professor Owen thinks that "one cannot reasonably suppose that the nature and properties of the nucleus of the impregnated germ-cell and that of the monad can be different."[95] And hence he further infers that "the nucleus of the monad is of a nature similar to, if not identical with," the matter of the spermatozoon. But we have seen that in the monad the nucleus is the co-ordinating part; and hence to say that the sperm-cell is, in nature, identical with it, is to say that the sperm-cell consists of co-ordinating matter.

Chemical analysis affords further evidence, though, from the imperfect data at present obtained, less conclusive evidence than could be wished. Partly from the white and gray nervous substances having been analysed together instead of separately, and partly from the difficulty of isolating the efficient contents of the sperm-cells, a satisfactory comparison cannot be made. Nevertheless, possessing in common, as they do, one element, by which they are specially characterised, the analysis, as far as it goes, supports our argument. The following table, which has been made up from data given in the _Cyclopædia of Anatomy and Physiology, Art._ NERVOUS SYSTEM, gives the proportion of this element in the brain in different conditions, and shows how important is its presence.

+-----------------------------+--------+-------+-------+--------+-------+ | | In | In | In | In | In | | |Infants.| Youth.|Adults.|Old Men.|Idiots.| | +--------+-------+-------+--------+-------+ | Solid constituents in a | | | | | | | hundred parts of the brain | 17.21 | 25.74 | 27.49 | 26.15 | 29.07 | | Of these solid constituents | | | | | | | the phosphorus amounts to | 0.8 | 1.65 | 1.80 | 1.00 | 0.85 | | Which gives a percentage of | | | | | | | phosphorus in the solid | | | | | | | constituents of | 4.65 | 6.41 | 6.54 | 3.82 | 2.92 | +-----------------------------+--------+-------+-------+--------+-------+

This connection between the quantity of phosphorus present and the degree of mental power exhibited, is sufficiently significant; and the fact that in the same individual the varying degrees of cerebral activity are indicated by the varying quantities of alkaline phosphates excreted by the kidneys,[96] still more clearly shows the essentialness of phosphorus as a constituent of nervous matter. Respecting the constitution of sperm-cells chemists do not altogether agree. One thing, however, is certain--that they contain unoxidized phosphorus; and also a fatty acid, that is not improbably similar to the fatty acid contained in neurine.[97] In fact, there would seem to be present the constituents of that oleophosphoric acid which forms so distinctive an element of the brain. That a large quantity of binoxide of protein is also present, may be ascribed to the fact that a great part of the sperm-cell consists merely of the protective membrane and its locomotive appendage; the really efficient portion being but the central contents.[98]

Evidence of a more conclusive nature--evidence, too, which will show in what direction our argument tends--is seen in the marked antagonism of the nervous and generative systems. Thus, the fact that intense mental application, involving great waste of the nervous tissues, and a corresponding consumption of nervous matter for their repair, is accompanied by a cessation in the production of sperm-cells, gives strong support to the hypothesis that the sperm-cells consist essentially of neurine. And this becomes yet clearer on finding that the converse fact is true--that undue production of sperm-cells involves cerebral inactivity. The first result of a morbid excess in this direction is headache, which may be taken to indicate that the brain is out of repair; this is followed by stupidity; should the disorder continue, imbecility supervenes, ending occasionally in insanity.

That the sperm-cell is co-ordinating matter, and the germ-cell matter to be co-ordinated, is, therefore, an hypothesis not only having much _à priori_ probability, but one supported by numerous facts.

§ 13. This hypothesis alike explains, and is confirmed by, the truth, that throughout the vertebrate tribes the degree of fertility varies inversely as the development of the nervous system.

The necessary antagonism of Individuation and Reproduction does indeed show itself amongst the higher animals, in some degree in the manner hitherto traced; namely, as determining the total bulk. Though the parts now thrown off, being no longer segments or gemmæ, are not obvious diminutions of the parent, yet they must be really such. Under the form of internal fission, the separative tendency is as much opposed to the aggregative tendency as ever; and, _other things equal_, the greater or less development of the individual depends upon the less or greater production of new individuals or germs of new individuals. As in groups of cells, and series of groups of cells, we saw that there was in each species a limit, passing which, the germ product would not remain united; so in each species of higher animal there is a limit, passing which, the process of cell-multiplication results in the throwing off of cells, instead of resulting in the formation of more tissue. Hence, taking an average view, we see why the smaller animals so soon arrive at a reproductive age, and produce large and frequent broods; and why, conversely, increased size is accompanied by retarded and diminished fertility.

But, as above implied, it is not so much to the bulk of the body as a whole, as to the bulk of the nervous system, that fertility stands related amongst the higher animals. Probably, indeed, it stands thus related in all cases; the difference simply arising from the fact, that whereas in the lower organisms, where the nervous system is not concentrated, its bulk varies as the bulk of the body, in the higher organisms it does not do so. Be this as it may, however, we see clearly that, amongst the vertebrata, the bodily development is not the determining circumstance. In a fish, a reptile, a bird, and a mammal of the same weight, there is nothing like equality of fecundity. Cattle and horses, arriving as they do so soon at a reproductive age, are much more prolific than the human race, at the same time that they are much larger. And whilst, again, the difference in size between the elephant and man is far greater, their respective powers of multiplication are less unlike. Looking in these cases at the nervous systems, however, we find no such discrepancy. On learning that the average ratio of the brain to the body is--in fishes, 1 to 5668; in reptiles, 1 to 1321; in birds, 1 to 212; and in mammals, 1 to 186;[99] their different degrees of fecundity are accounted for. Though an ox will outweigh half-a-dozen men, yet its brain and spinal cord are far less than those of one man; and though in bodily development the elephant so immensely exceeds the human being, yet the elephant's cerebro-spinal system is only thrice the size attained by that of civilized men.[100] Unfortunately, it is impossible to trace throughout the animal kingdom this inverse relationship between the nervous and reproductive systems with any accuracy. Partly from the fact that, in each case, the degree of fertility depends on three variable elements--the age at which reproduction begins, the number produced at a birth, and the frequency of the births; partly from the fact that, in respect to most animals, these data are not satisfactorily attainable, and that, when they are attainable, they are vitiated by the influence of domesticity; and partly from the fact that no precise measurement of the respective nervous systems has been made, we are unable to draw any but general and somewhat vague comparisons. These, however, as far as they go, are in our favour. Ascending from beings of the acrite nerveless type, which are the most prolific of all, through the various invertebrate sub-kingdoms, amongst which spontaneous fission disappears as the nervous system becomes developed; passing again to the least nervous and most fertile of the vertebrate series--Fishes, of which, too, the comparatively large-brained cartilaginous kinds multiply much less rapidly than the others; progressing through the more highly endowed and less prolific Reptiles to the Mammalia, amongst which the Rodents, with their unconvoluted brains, are noted for their fecundity; and ending with man and the elephant, the least fertile and largest-brained of all--there seems to be throughout a constant relationship between these attributes.

And indeed, on turning back to our _à priori_ principle, no other relationship appears possible. We found it to be the necessary law of maintenance of races, that the ability to maintain individual life and the ability to multiply vary inversely. But the ability to maintain individual life _is in all cases measured by the development of the nervous system_. If it be in good visceral organization that the power of self-preservation is shown, this implies some corresponding nervous apparatus to secure sufficient food. If it be in strength, there must be a provision of nerves and nervous centres answering to the number and size of the muscles. If it be in swiftness and agility, a proportionate development of the cerebellum is presupposed. If it be in intelligence, this varies with the size of the cerebrum. As in all cases co-ordination of actions constitutes the life, or, what is the same thing, the ability to maintain life; and as throughout the animal kingdom this co-ordination, under all its forms, is effected by nervous agents of some kind or other; and as each of these nervous agents performs but one function; it follows that in proportion to the number of the actions co-ordinated must be the number of nervous agents. Hence the nervous system becomes the universal measure of the degree of co-ordination of actions; that is, of the life, or ability to maintain life. And if the nervous system varies directly as the ability to maintain life, it _must_ vary inversely as the ability to multiply.[101]

And here, assuming the constitution of the sperm-cell above inferred to be the true one, we see how the obverse _à priori_ principle is fulfilled. Where, as amongst the lowest organisms, bulk is expressive of life, the antagonism of individuation and reproduction was broadly exhibited in the fact that the making of two or more new individuals was the _un_making of the original individual. And now, amongst the higher organisms, where bulk is no longer the measure of life, we see that this antagonism is between the neural elements thrown off, and that internal neural mass whose bulk _is_ the measure of life. The production of co-ordinating cells must be at the expense of the co-ordinating apparatus; and the aggregation of the co-ordinating apparatus must be at the expense of co-ordinating cells. How the antagonism affects the female economy is not so clear. Possibly the provision required to be made for supplying nervous as well as other nutriment to the embryo, involves an arrest in the development of the nervous system; and if so, probably this arrest takes place early in proportion as the number of the coming offspring makes the required provision great: or rather, to put the facts in their right sequence, an early arrest renders the production of a numerous offspring possible.

§ 14. The law which we have thus traced throughout the animal kingdom, and which must alike determine the different fertilities of different species, and the variations of fertility in the same species, we have now to consider in its application to mankind.

[_The remainder of the essay, which as implied, deals with the application of this general principle to the multiplication of the human race, need not be here reproduced. The subject is treated in full in Part VI._]

APPENDIX B.

THE INADEQUACY OF NATURAL SELECTION, ETC., ETC.

[_In this Appendix are included four essays originally published in the_ Contemporary Review _and subsequently republished as pamphlets. The first appeared under the above title in February and March, 1893; the second in May of that year under the title "Prof. Weismann's Theories;" the third in December of that year under the title "A Rejoinder to Prof. Weismann;" and the fourth in October, 1894, under the title "Weismannism Once More." As these successive essays practically form parts of one whole, I have thought it needless to keep them separate by repeating their titles, and have simply marked them off from one another by the numbers I, II, III, IV. Of course, as they are components of a controversy, some incompleteness arises from the absence of the essays to which portions of them were replies; but in each the course of the argument sufficiently indicates the counter-arguments which were met._]

I.

Students of psychology are familiar with the experiments of Weber on the sense of touch. He found that different parts of the surface differ widely in their ability to give information concerning the things touched. Some parts, which yielded vivid sensations, yielded little or no knowledge of the sizes or forms of the things exciting them; whereas other parts, from which there came sensations much less acute, furnished clear impressions respecting the tangible characters, even of relatively small objects. These unlikenesses of tactual discriminativeness he ingeniously expressed by actual measurements. Taking a pair of compasses, he found that if they were closed so nearly that the points were less than one-twelfth of an inch apart, the end of the forefinger could not perceive that there were two points: the two points seemed one. But when the compasses were opened so that the points were one-twelfth of an inch apart, then the end of the forefinger distinguished the two points. At the same time, he found that the compasses must be opened to the extent of two and a half inches, before the middle of the back could distinguish between two points and one. That is to say, as thus measured, the end of the forefinger has thirty times the tactual discriminativeness which the middle of the back has.

Between these extremes he found gradations. The inner surfaces of the second joints of the fingers can distinguish separateness of positions only half as well as the tip of the forefinger. The innermost joints are still less discriminating, but have powers of discrimination equal to that of the tip of the nose. The end of the great toe, the palm of the hand, and the cheek, have alike one-fifth of the perceptiveness which the tip of the forefinger has; and the lower part of the forehead has but one-half that possessed by the cheek. The back of the hand and the crown of the head are nearly alike in having but a fourteenth or a fifteenth of the ability to perceive positions as distinct, which is possessed by the finger-end. The thigh, near the knee, has rather less, and the breast less still; so that the compasses must be opened more than an inch and a half before the breast distinguishes the two points from one another.

What is the meaning of these differences? How, in the course of evolution, have they been established? If "natural selection," or survival of the fittest, is the assigned cause, then it is required to show in what way each of these degrees of endowment has advantaged the possessor to such extent that not infrequently life has been directly or indirectly preserved by it. We might reasonably assume that in the absence of some differentiating process, all parts of the surface would have like powers of perceiving relative positions. They cannot have become widely unlike in perceptiveness without some cause. And if the cause alleged is natural selection, then it is necessary to show that the greater degree of the power possessed by this part than by that, has not only conduced to the maintenance of life, but has conduced so much that an individual in whom a variation has produced better adjustment to needs, thereby maintained life when some others lost it; and that among the descendants inheriting this variation, there was a derived advantage such as enabled them to multiply more than the descendants of individuals not possessing it. Can this, or anything like this, be shown?

That the superior perceptiveness of the forefinger-tip has thus arisen, might be contended with some apparent reason. Such perceptiveness is an important aid to manipulation, and may have sometimes given a life-saving advantage. In making arrows or fish-hooks, a savage possessing some extra amount of it may have been thereby enabled to get food where another failed. In civilized life, too, a sempstress with well-endowed finger-ends might be expected to gain a better livelihood than one with finger-ends which were obtuse; though this advantage would not be so great as appears. I have found that two ladies whose finger-ends were covered with glove-tips, reducing their sensitiveness from one-twelfth of an inch between compass-points to one-seventh, lost nothing appreciable of their quickness and goodness in sewing. An experience of my own here comes in evidence. Towards the close of my salmon-fishing days I used to observe what a bungler I had become in putting on and taking off artificial flies. As the tactual discriminativeness of my finger-ends, recently tested, comes up to the standard specified by Weber, it is clear that this decrease of manipulative power, accompanying increase of age, was due to decrease in the delicacy of muscular co-ordination and sense of pressure--not to decrease of tactual discriminativeness. But not making much of these criticisms, let us admit the conclusion that this high perceptive power possessed by the forefinger-end may have arisen by survival of the fittest; and let us limit the argument to the other differences.

How about the back of the trunk and its face? Is any advantage derived from possession of greater tactual discriminativeness by the last than the first? The tip of the nose has more than three times the power of distinguishing relative positions which the lower part of the forehead has. Can this greater power be shown to have any advantage? The back of the hand has scarcely more discriminative ability than the crown of the head, and has only one-fourteenth of that which the finger-tip has. Why is this? Advantage might occasionally be derived if the back of the hand could tell us more than it does about the shapes of the surfaces touched. Why should the thigh near the knee be twice as perceptive as the middle of the thigh? And, last of all, why should the middle of the forearm, middle of the thigh, middle of the back of the neck, and middle of the back, all stand on the lowest level, as having but one-thirtieth of the perceptive power which the tip of the forefinger has? To prove that these differences have arisen by natural selection, it has to be shown that such small variation in one of the parts as might occur in a generation--say one-tenth extra amount--has yielded an appreciably greater power of self-preservation; and that those inheriting it have continued to be so far advantaged as to multiply more than those who, in other respects equal, were less endowed with this trait. Does any one think he can show this?

But if this distribution of tactual perceptiveness cannot be explained by survival of the fittest, how can it be explained? The reply is that, if there has been in operation a cause which it is now the fashion among biologists to ignore or deny, these various differences are at once accounted for. This cause is the inheritance of acquired characters. As a preliminary to setting forth the argument showing this, I have made some experiments.

It is a current belief that the fingers of the blind, more practised in tactual exploration than the fingers of those who can see, acquire greater discriminativeness: especially the fingers of those blind who have been taught to read from raised letters. Not wishing to trust to this current belief, I recently tested two youths, one of fifteen and the other younger, at the School for the Blind in Upper Avenue Road, and found the belief to be correct. I found that instead of being unable to distinguish between points of the compasses until they were opened to one-twelfth of an inch apart, both of them could distinguish between points when only one-fourteenth of an inch apart. They had thick and coarse skins; and doubtless, had the intervening obstacle, so produced, been less, the discriminative power would have been greater. It afterwards occurred to me that a better test would be furnished by those whose finger-ends are exercised in tactual perceptions, not occasionally, as by the blind in reading, but all day long in pursuit of their occupations. The facts answered expectation. Two skilled compositors, on whom I experimented, were both able to distinguish between points when they were only one-seventeenth of an inch apart. Thus we have clear proof that constant exercise of the tactual nervous structure leads to further development.[102]

Now if acquired structural traits are inheritable, the various contrasts above set down are obvious consequences; for the gradations in tactual perceptiveness correspond with the gradations in the tactual exercises of the parts. Save by contact with clothes, which present only broad surfaces having but slight and indefinite contrast, the trunk has scarcely any converse with external bodies, and it has but small discriminative power; but what discriminative power it has is greater on its face than on its back, corresponding to the fact that the chest and abdomen are much more frequently explored by the hands: this difference being probably in part inherited from inferior creatures; for, as we may see in dogs and cats, the belly is far more accessible to feet and tongue than the back. No less obtuse than the back are the middle of the back of the neck, the middle of the forearm, and the middle of the thigh; and these parts have but rare experiences of irregular foreign bodies. The crown of the head is occasionally felt by the fingers, as also the back of one hand by the fingers of the other; but neither of these surfaces, which are only twice as perceptive as the back, is used with any frequency for touching objects, much less for examining them. The lower part of the forehead, though more perceptive than the crown of the head, in correspondence with a somewhat greater converse with the hands, is less than one-third as perceptive as the tip of the nose; and manifestly, both in virtue of its relative prominence, in virtue of its contacts with things smelt at, and in virtue of its frequent acquaintance with the handkerchief, the tip of the nose has far greater tactual experience. Passing to the inner surfaces of the hands, which, taken as wholes, are more constantly occupied in touching than are the back, breast, thigh, forearm, forehead, or back of the hand, Weber's scale shows that they are much more perceptive, and that the degrees of perceptiveness of different parts correspond with their tactual activities. The palms have but one-fifth the perceptiveness possessed by the forefinger-ends; the inner surfaces of the finger-joints next the palms have but one-third; while the inner surfaces of the second joints have but one-half. These abilities correspond with the facts that whereas the inner parts of the hand are used only in grasping things, the tips of the fingers come into play not only when things are grasped, but when such things, as well as smaller things, are felt at or manipulated. It needs but to observe the relative actions of these parts in writing, in sewing, in judging textures, &c., to see that above all other parts the finger-ends, and especially the forefinger-ends, have the most multiplied experiences. If, then, it be that the extra perceptiveness acquired from actual tactual activities, as in a compositor, is inheritable, these gradations of tactual perceptiveness are explained.

Doubtless some of those who remember Weber's results, have had on the tip of the tongue the argument derived from the tip of the tongue. This part exceeds all other parts in power of tactual discrimination: doubling, in that respect, the power of the forefinger-tip. It can distinguish points that are only one-twenty-fourth of an inch apart. Why this unparalleled perceptiveness? If survival of the fittest be the ascribed cause, then it has to be shown what the advantages achieved have been; and, further, that those advantages have been sufficiently great to have had effects on the maintenance of life.

Besides tasting, there are two functions conducive to life, which the tongue performs. It enables us to move about food during mastication, and it enables us to make many of the articulations constituting speech. But how does the extreme discriminativeness of the tongue-tip aid these functions? The food is moved about, not by the tongue-tip, but by the body of the tongue; and even were the tip largely employed in this process, it would still have to be shown that its ability to distinguish between points one-twenty-fourth of an inch apart, is of service to that end, which cannot be shown. It may, indeed, be said that the tactual perceptiveness of the tongue-tip serves for detection of foreign bodies in the food, as plum-stones or as fish-bones. But such extreme perceptiveness is needless for the purpose. A perceptiveness equal to that of the finger-ends would suffice. And further, even were such extreme perceptiveness useful, it could not have caused survival of individuals who possessed it in slightly higher degrees than others. It needs but to observe a dog crunching small bones, and swallowing with impunity the sharp-angled pieces, to see that but a very small amount of mortality would be prevented.

But what about speech? Well, neither here can there be shown any advantage derived from this extreme perceptiveness. For making the _s_ and _z_, the tongue has to be partially applied to a portion of the palate next the teeth. Not only, however, must the contact be incomplete, but its place is indefinite--may be half an inch further back. To make the _sh_ and _zh_, the contact has to be made, not with the tip, but with the upper surface of the tongue; and must be an incomplete contact. Though, for making the liquids, the tip of the tongue and the sides of the tongue are used, yet the requisite is not any exact adjustment of the tip, but an imperfect contact with the palate. For the _th_, the tip is used along with the edges of the tongue; but no perfect adjustment is required, either to the edges of the teeth, or to the junction of the teeth with the palate, where the sound may equally well be made. Though for the _t_ and _d_ complete contact of the tip and edges of the tongue with the palate is required, yet the place of contact is not definite, and the tip takes no more important share in the action than the sides. Any one who observes the movements of his tongue in speaking, will find that there occur no cases in which the adjustments must have an exactness corresponding to the extreme power of discrimination which the tip possesses: for speech, this endowment is useless. Even were it useful, it could not be shown that it has been developed by survival of the fittest; for though perfect articulation is an aid, yet imperfect articulation has rarely such an effect as to impede a man in the maintenance of his life. If he is a good workman, a German's interchanges of _b's_ and _p's_ do not disadvantage him. A Frenchman who, in place of the sound of _th_, always makes the sound of _z_, succeeds as a teacher of music or dancing, no less than if he achieved the English pronunciation. Nay, even such an imperfection of speech as that which arises from cleft palate, does not prevent a man from getting on if he is capable. True, it may go against him as a candidate for Parliament, or as an "orator" of the unemployed (mostly not worth employing). But in the struggle for life he is not hindered by the effect to the extent of being less able than others to maintain himself and his offspring. Clearly, then, even if this unparalleled perceptiveness of the tongue-tip is required for perfect speech, such use is not sufficiently important to have been developed by natural selection.

How, then, is this remarkable trait of the tongue-tip to be accounted for? Without difficulty, if there is inheritance of acquired characters. For the tongue-tip has, above all other parts of the body, unceasing experiences of small irregularities of surface. It is in contact with the teeth, and either consciously or unconsciously is continually exploring them. There is hardly a moment in which impressions of adjacent but different positions are not being yielded to it by either the surfaces of the teeth or their edges; and it is continually being moved about from some of them to others. No advantage is gained. It is simply that the tongue's position renders perpetual exploration almost inevitable; and by perpetual exploration is developed this unique power of discrimination. Thus the law holds throughout, from this highest degree of perceptiveness of the tongue-tip to its lowest degree on the back of the trunk; and no other explanation of the facts seems possible.

"Yes, there is another explanation," I hear some one say: "they may be explained by _panmixia_." Well, in the first place, as the explanation by _panmixia_ implies that these gradations of perceptiveness have been arrived at by the dwindling of nervous structures, there lies at the basis of the explanation an unproved and improbable assumption; and, in the second place, even were there no such difficulty, it may with certainty be denied that _panmixia_ can furnish an explanation. Let us look at its pretensions.

* * * * *

It was not without good reason that Bentham protested against metaphors. Figures of speech in general, valuable as they are in poetry and rhetoric, cannot be used without danger in science and philosophy. The title of Mr. Darwin's great work furnishes us with an instance of the misleading effects produced by them. It runs:--_The Origin of Species by means of Natural Selection, or the Preservation of favoured Races in the Struggle for Life_. Here are two figures of speech which conspire to produce an impression more or less erroneous. The expression "natural selection" was chosen as serving to indicate some parallelism with artificial selection--the selection exercised by breeders. Now selection connotes volition, and thus gives to the thoughts of readers a wrong bias. Some increase of this bias is produced by the words in the second title, "favoured races;" for anything which is favoured implies the existence of some agent conferring a favour. I do not mean that Mr. Darwin himself failed to recognize the misleading connotations of his words, or that he did not avoid being misled by them. In chapter iv of the _Origin of Species_, he says that, considered literally, "natural selection is a false term," and that the personification of Nature is objectionable; but he thinks that readers, and those who adopt his views, will soon learn to guard themselves against the wrong implications. Here I venture to think that he was mistaken. For thinking this, there is the reason that even his disciple, Mr. Wallace--no, not his disciple, but his co-discoverer, ever to be honoured--has apparently been influenced by them. When, for example, in combating a view of mine, he says that "the very thing said to be impossible by variation and natural selection has been again and again effected, by variation and artificial selection," he seems clearly to imply that the processes are analogous, and operate in the same way. Now this is untrue. They are analogous only within certain narrow limits; and, in the great majority of cases, natural selection is utterly incapable of doing that which artificial selection does.

To see this it needs only to de-personalise Nature, and to remember that, as Mr. Darwin says, Nature is "only the aggregate action and product of many natural laws [forces]." Observe its relative shortcomings. Artificial selection can pick out a particular trait, and, regardless of other traits of the individuals displaying it, can increase it by selective breeding in successive generations. For, to the breeder or fancier, it matters little whether such individuals are otherwise well constituted. They may be in this or that way so unfit for carrying on the struggle for life, that were they without human care, they would disappear forthwith. On the other hand, if we regard Nature as that which it is, an assemblage of various forces, inorganic and organic, some favourable to the maintenance of life and many at variance with its maintenance--forces which operate blindly--we see that there is no such selection of this or that trait; but that there is a selection only of individuals which are, by the aggregate of their traits, best fitted for living. And here I may note an advantage possessed by the expression "survival of the fittest;" since this does not tend to raise the thought of any one character which, more than others, is to be maintained or increased; but tends rather to raise the thought of a general adaptation for all purposes. It implies the process which Nature can alone carry on--the leaving alive of those which are best able to utilize surrounding aids to life, and best able to combat or avoid surrounding dangers. And while this phrase covers the great mass of cases in which there are preserved well-constituted individuals, it also covers those special cases which are suggested by the phrase "natural selection," in which individuals succeed beyond others in the struggle for life, by the help of particular characters which conduce in important ways to prosperity and multiplication. For now observe the fact which here chiefly concerns us, that survival of the fittest can increase any serviceable trait, only if that trait conduces to prosperity of the individual, or of posterity, or of both, _in an important degree_. There can be no increase of any structure by natural selection unless, amid all the slightly varying structures constituting the organism, increase of this particular one is so advantageous as to cause greater multiplication of the family in which it arises than of other families. Variations which, though advantageous, fail to do this, must disappear again. Let us take a case.

Keenness of scent in a deer, by giving early notice of approaching enemies, subserves life so greatly that, other things equal, an individual having it in an unusual degree is more likely than others to survive; and, among descendants, to leave some similarly endowed or more endowed, who again transmit the variation with, in some cases, increase. Clearly this highly useful power may be developed by natural selection. So also, for like reasons, may quickness of vision and delicacy of hearing; though it may be remarked in passing that since this extra sense-endowment, serving to give early alarm, profits the herd as a whole, which takes the alarm from one individual, selection of it is not so easy, unless it occurs in a conquering stag. But now suppose that one member of the herd--perhaps because of more efficient teeth, perhaps by greater muscularity of stomach, perhaps by secretion of more appropriate gastric juices--is enabled to eat and digest a not uncommon plant which the others refuse. This peculiarity may, if food is scarce, conduce to better self-maintenance, and better fostering of young if the individual is a hind. But unless this plant is abundant, and the advantage consequently great, the advantages which other members of the herd gain from other slight variations may be equivalent. This one has unusual agility, and leaps a chasm which others balk at. That one develops longer hair in winter, and resists the cold better. Another has a skin less irritated by flies, and can graze without so much interruption. Here is one which has an unusual power of detecting food under the snow; and there is one which shows extra sagacity in the choice of a shelter from wind and rain. That the variation giving ability to eat a plant before unutilized, may become a trait of the herd, and eventually of a variety, it is needful that the individual in which it occurs shall have more descendants, or better descendants, or both, than have the various other individuals severally having their small superiorities. If these other individuals severally profit by their small superiorities, and transmit them to equally large numbers of offspring, no increase of the variation in question can take place: it must soon be cancelled. Whether in the _Origin of Species_ Mr. Darwin has recognized this fact, I do not remember, but he has certainly done it by implication in his _Animals and Plants under Domestication_. Speaking of variations in domestic animals, he there says that "any particular variation would generally be lost by crossing, reversion, and the accidental destruction of the varying individuals, unless carefully preserved by man." (Vol. II, p. 292.) That which survival of the fittest does in cases like the one I have instanced, is to keep all faculties up to the mark, by destroying such individuals as have faculties in some respect below the mark; and it can produce development of some one faculty only if that faculty is predominantly important. It seems to me that many naturalists have practically lost sight of this, and assume that natural selection will increase _any_ advantageous trait. Certainly a view now held by some assumes as much.

The consideration of this view, to which the foregoing paragraph is introductory, may now be entered upon. This view concerns, not direct selection, but what has been called, in questionable logic, "reversed selection"--the selection which effects, not increase of an organ, but decrease of it. For as, under some conditions, it is of advantage to an individual and its descendants to have some structure of larger size, it may be, under other conditions--namely, when the organ becomes useless--of advantage to have it of smaller size; since, even if it is not in the way, its weight and the cost of its nutrition are injurious taxes on the organism. But now comes the truth to be emphasized. Just as direct selection can increase an organ only in certain cases, so can reversed selection decrease it only in certain cases. Like the increase produced by a variation, the decrease produced by one must be such as will sensibly conduce to preservation and multiplication. It is, for instance, conceivable that were the long and massive tail of the kangaroo to become useless (say by the forcing of the species into a mountainous and rocky habitat filled with brushwood), a variation which considerably reduced the tail might sensibly profit the individual in which it occurred; and, in seasons when food was scarce, might cause survival when individuals with large tails died. But the economy of nutrition must be considerable before any such result could occur. Suppose that in this new habitat the kangaroo had no enemies; and suppose that, consequently, quickness of hearing not being called for, large ears gave no greater advantage than small ones. Would an individual with smaller ears than usual, survive and propagate better than other individuals, in consequence of the economy of nutrition achieved? To suppose this is to suppose that the saving of a grain or two of protein per day would determine the kangaroo's fate.

Long ago I discussed this matter in the _Principles of Biology_ (§ 166), taking as an instance the decrease of the jaw implied by the crowding of the teeth, and now proved by measurement to have taken place. Here is the passage:--

"No functional superiority possessed by a small jaw over a large jaw, in civilized life, can be named as having caused the more frequent survival of small-jawed individuals. The only advantage which smallness of jaw might be supposed to give, is the advantage of economized nutrition; and this could not be great enough to further the preservation of men possessing it. The decrease of weight in the jaw and co-operative parts that has arisen in the course of many thousands of years, does not amount to more than a few ounces. This decrease has to be divided among the many generations that have lived and died in the interval. Let us admit that the weight of these parts diminished to the extent of an ounce in a single generation (which is a large admission); it still cannot be contended that the having to carry an ounce less in weight, or having to keep in repair an ounce less of tissue, could sensibly affect any man's fate. And if it never did this--nay, if it did not cause a _frequent_ survival of small-jawed individuals where large-jawed individuals died, natural selection could neither cause nor aid diminution of the jaw and its appendages."

When writing this passage in 1864, I never dreamt that a quarter of a century later, the supposable cause of degeneration here examined and excluded as impossible, would be enunciated as an actual cause and named "reversed selection."

One of the arguments used to show the adequacy of natural selection under its direct or indirect form consists of a counter-argument to the effect that inheritance of functionally-wrought changes, supposing it to be operative, does not explain certain of the facts. This is alleged by Prof. Weismann as a part justification for his doctrine of Panmixia. Concerning the "blind fish and amphibia" found in dark places, which have but rudimentary eyes "hidden under the skin," he argues that "it is difficult to reconcile the facts of the case with the ordinary theory that the eyes of these animals have simply degenerated through disuse." After giving instances of rapid degeneration of disused organs, he argues that if "the effects of disuse are so striking in a single life, we should certainly expect, if such effects can be transmitted, that all traces of an eye would soon disappear from a species which lives in the dark." Doubtless this is a reasonable conclusion. To explain the facts on the hypothesis that acquired characters are inheritable, seems very difficult. One possible explanation may, indeed, be named. It appears to be a general law of organization that structures are stable in proportion to their antiquity--that while organs of relatively modern origin have but a comparatively superficial root in the constitution, and readily disappear if the conditions do not favour their maintenance, organs of ancient origin have deep-seated roots in the constitution, and do not readily disappear. Having been early elements in the type, and having continued to be reproduced as parts of it during a period extending throughout many geological epochs, they are comparatively persistent. Now the eye answers to this description as being a very early organ. But waiving possible explanations, let us take the particular instance cited by Prof. Weismann and see what is to be made of it. He writes:--

"The caverns in Carniola and Carinthia, in which the blind _Proteus_ and so many other blind animals live, belong geologically to the Jurassic formation; and although we do not exactly know when for example the _Proteus_ first entered them, the low organization of this amphibian certainly indicates that it has been sheltered there for a very long period of time, and that thousands of generations of this species have succeeded one another in the caves.

"Hence there is no reason to wonder at the extent to which the degeneration of the eye has been already carried in the _Proteus_; even if we assume that it is merely due to the cessation of the conserving influence of natural selection."[103]

Let me first note a strange oversight on the part of Prof. Weismann. He points out that the caverns in question belong to the Jurassic formation: apparently intending to imply that they have an antiquity related to that of the formation. But there is no such relation, except that the caverns cannot be older than the formation. They may have originated at any period since the containing strata were deposited; and they may be therefore relatively modern. But passing over this, and admitting that the _Proteus_ has inhabited the caverns for an enormous period, what is to be said of the fact that their eyes have not disappeared entirely, as Prof. Weismann contends they should have done had the inheritance of the effects of disuse been all along operative? There is a very sufficient answer--the rudimentary eyes are not entirely useless. It seems that when the underground streams it inhabits are unusually swollen, some individuals of the species are carried out of the caverns into the open (being then sometimes captured). It is also said that the creatures shun the light; this trait being, I presume, observed when it is in captivity. Now obviously, among individuals carried out into the open, those which remain visible are apt to be carried off by enemies; whereas, those which, appreciating the difference between light and darkness, shelter themselves in dark places, survive. Hence the tendency of natural selection is to prevent the decrease of the eyes beyond that point at which they can distinguish between light and darkness. Thus the apparent anomaly is explained.

Let me suggest, as another possible reason for persistence of rudimentary organs, that the principle of economy of growth will cause diminution of them only in proportion as their constituents are of value for other uses in the organism; and that in many cases their constituents are practically valueless. Hence probably the reason why, in the case of stalk-eyed crustaceans, the eye is gone but the pedicle remains, or to use Mr. Darwin's simile, the telescope has disappeared but not its stand.

* * * * *

Along with that inadequacy of natural selection to explain changes of structure which do not aid life in important ways, alleged in § 166 of _The Principles of Biology_, a further inadequacy was alleged. It was contended that the relative powers of co-operative parts cannot be adjusted solely by survival of the fittest; and especially where the parts are numerous and the co-operation complex. In illustration it was pointed out that immensely developed horns, such as those of the extinct Irish elk, weighing over a hundred-weight, could not, with the massive skull bearing them, be carried at the extremity of the outstretched neck without many and great modifications of adjacent bones and muscles of the neck and thorax; and that without strengthening of the fore-legs, too, there would be failure alike in fighting and in locomotion. And it was argued that while we cannot assume spontaneous increase of all these parts proportionate to the additional strains, we cannot suppose them to increase by variations, one at once, without supposing the creature to be disadvantaged by the weight and nutrition of parts that were for the time useless--parts, moreover, which would revert to their original sizes before the other needful variations occurred.

When, in reply to me, it was contended that co-operative parts vary together, I named facts conflicting with this assertion--the fact that the blind cray-fish of the Kentucky caves have lost their eyes but not the foot-stalks carrying them; the fact that the normal proportion between tongue and beak in certain selected varieties of pigeons is lost; the fact that lack of concomitance in decrease of jaws and teeth in sundry kinds of pet dogs, has caused great crowding of the teeth ("The Factors of Organic Evolution," _Essays_, i, 401-402). And I then argued that if co-operative parts, small in number and so closely associated as these are, do not vary together, it is unwarrantable to allege that co-operative parts which are very numerous and remote from one another vary together. After making this rejoinder I enforced my argument by a further example--that of the giraffe. Tacitly recognizing the truth that the unusual structure of this creature must have been, in its most conspicuous traits, the result of survival of the fittest (since it is absurd to suppose that efforts to reach high branches could lengthen the legs), I illustrated afresh the obstacles to co-adaptation. Not dwelling on the objection that increase of any components of the fore-quarters out of adjustment to the others, would cause evil rather than good, I went on to argue that the co-adaptation of parts required to make the giraffe's structure useful, is much greater than at first appears. This animal has a grotesque gallop, necessitated by the great difference in length between the fore and the hind limbs. I pointed out that the mode of action of the hind limbs shows that the bones and muscles have all been changed in their proportions and adjustments; and I contended that, difficult as it is to believe that all parts of the fore-quarters have been co-adapted by the appropriate variations, now of this part now of that, it becomes impossible to believe that all the parts in the hind-quarters have been simultaneously co-adapted to one another and to all the parts of the fore-quarters: adding that want of co-adaptation, even in a single muscle, would cause fatal results when high speed had to be maintained while escaping from an enemy.

Since this argument, repeated with this fresh illustration, was published in 1886, I have met with nothing to be called a reply; and might, I think, if convictions usually followed proofs, leave the matter as it stands. It is true that, in his _Darwinism_, Mr. Wallace has adverted to my renewed objection, and, as already said, contended that changes such as those instanced can be effected by natural selection, since such changes can be effected by artificial selection: a contention which, as I have pointed out, assumes a parallelism that does not exist. But now, instead of pursuing the argument further along the same line, let me take a somewhat different line.

If there occurs some change in an organ, say by increase of its size, which adapts it better to the creature's needs, it is admitted that when, as commonly happens, the use of the organ demands the co-operation of other organs, the change in it will generally be of no service unless the co-operative organs are changed. If, for instance, there takes place such a modification of a rodent's tail as that which, by successive increases, produces the trowel-shaped tail of the beaver, no advantage will be derived unless there also take place certain modifications in the bulks and shapes of the adjacent vertebræ and their attached muscles, as well as, probably, in the hind limbs; enabling them to withstand the reactions of the blows given by the tail. And the question is, by what process these many parts, changed in different degrees, are co-adapted to the new requirements--whether variation and natural selection alone can effect the readjustment. There are three conceivable ways in which the parts may simultaneously change:--(1) they may all increase or decrease together in like degree; (2) they may all simultaneously increase or decrease independently, so as not to maintain their previous proportions, or assume any other special proportions; (3) they may vary in such ways and degrees as to make them jointly serviceable for the new end. Let us consider closely these several conceivabilities.

And first of all, what are we to understand by co-operative parts? In a general sense, all the organs of the body are co-operative parts, and are respectively liable to be more or less changed by change in any one. In a narrower sense, more directly relevant to the argument, we may, if we choose to multiply difficulties, take the entire framework of bones and muscles as formed of co-operative parts; for these are so related that any considerable change in the actions of some entails change in the actions of most others. It needs only to observe how, when putting out an effort, there goes, along with a deep breath, an expansion of the chest and a bracing up of the abdomen, to see that various muscles beyond those directly concerned are strained along with them. Or, when suffering from lumbago, an effort to lift a chair will cause an acute consciousness that not the arms only are brought into action, but also the muscles of the back. These cases show how the motor organs are so tied together that altered actions of some implicate others quite remote from them.

But without using the advantage which this interpretation of the words would give, let us take, as co-operative organs, those which are obviously such--the organs of locomotion. What, then, shall we say of the fore limbs and hind limbs of terrestrial mammals, which co-operate closely and perpetually? Do they vary together? If so, how have there been produced such contrasted structures as that of the kangaroo, with its large hind limbs and small fore limbs, and that of the giraffe, in which the hind limbs are small and the fore limbs large--how does it happen that, descending from the same primitive mammal, these creatures have diverged in the proportions of their limbs in opposite directions? Take, again, the articulate animals. Compare one of the lower types, with its rows of almost equal-sized limbs, and one of the higher types, as a crab or a lobster, with limbs some very small and some very large. How came this contrast to arise in the course of evolution, if there was the equality of variation supposed?

But now let us narrow the meaning of the phrase still further, giving it a more favourable interpretation. Instead of considering separate limbs as co-operative, let us consider the component parts of the same limb as co-operative, and ask what would result, from varying together. It would in that case happen that, though the fore and hind limbs of a mammal might become different in their sizes, they would not become different in their structures. If so, how have there arisen the unlikenesses between the hind legs of the kangaroo and those of the elephant? Or if this comparison is objected to, because the creatures belong to the widely different divisions of implacental and placental mammals, take the cases of the rabbit and the elephant, both belonging to the last division. On the hypothesis of evolution these are both derived from the same original form; but the proportions of the parts have become so widely unlike that the corresponding joints are scarcely recognized as such by the unobservant: at what seem corresponding places the legs bend in opposite ways. Equally marked, or more marked, is the parallel fact among the _Articulata_. Take that limb of the lobster which bears the claw and compare it with the corresponding limb in an inferior articulate animal, or the corresponding limb of its near ally, the rock lobster, and it becomes obvious that the component segments of the limb have come to bear to one another in the one case, proportions immensely different from those they bear in the other case. Undeniably, then, on contemplating the general facts of organic structure, we see that the concomitant variations in the parts of limbs, have not been of a kind to produce equal amounts of change in them, but quite the opposite--have been everywhere producing inequalities. Moreover, we are reminded that this production of inequalities among co-operative parts, is an essential principle of development. Had it not been so, there could not have been that progress from homogeneity of structure to heterogeneity of structure which constitutes evolution.

We pass now to the second supposition:--that the variations in co-operative parts occur irregularly, or in such independent ways that they bear no definite relations to one another--miscellaneously, let us say. This is the supposition which best corresponds with the facts. Glances at the faces around yield conspicuous proofs. Many of the muscles of the face and some of the bones, are distinctly co-operative; and these respectively vary in such ways as to produce in each person a different combination. What we see in the face we have reason to believe holds in the limbs and in all other parts. Indeed, it needs but to compare people whose arms are of the same lengths, and observe how stumpy are the fingers of one and how slender those of another; or it needs but to note the unlikenesses of gait of passers-by, implying small unlikenesses of structure; to be convinced that the relations among the variations of co-operative parts are anything but fixed. And now, confining our attention to limbs, let us consider what must happen if, by variations taking place miscellaneously, limbs have to be partially changed from fitness for one function to fitness for another function--have to be re-adapted. That the reader may fully comprehend the argument, he must here have patience while a good many anatomical details are set down.

Let us suppose a species of quadruped of which the members have, for immense past periods, been accustomed to locomotion over a relatively even surface, as, for instance, the "prairie-dogs" of North America; and let us suppose that increase of numbers has driven part of them into a region full of obstacles to easy locomotion--covered, say, by the decaying stems of fallen trees, such as one sees in portions of primeval forest. Ability to leap must then become a useful trait; and, according to the hypothesis we are considering, this ability will be produced by the selection of favourable variations. What are the variations required? A leap is effected chiefly by the bending of the hind limbs so as to make sharp angles at the joints, and then suddenly straightening them; as any one may see on watching a cat leap on to the table. The first required change, then, is increase of the large extensor muscles, by which the hind limbs are straightened. Their increases must be duly proportioned; for if those which straightened one joint become much stronger than those which straightened the other joint, the result must be collapse of the other joint when the muscles are contracted together. But let us make a large admission, and suppose these muscles to vary together; what further muscular change is next required? In a plantigrade mammal the metatarsal bones chiefly bear the reaction of the leap, though the toes may have a share. In a digitigrade mammal, however, the toes form almost exclusively the fulcrum, and if they are to bear the reaction of a higher leap, the flexor muscles which depress and bend them must be proportionately enlarged: if not, the leap will fail from want of a firm _point d'appui_. Tendons as well as muscles must be modified; and, among others, the many tendons which go to the digits and their phalanges. Stronger muscles and tendons imply greater strains on the joints; and unless these are strengthened, one or other, dislocation will be caused by a more vigorous spring. Not only the articulations themselves must be so modified as to bear greater stress, but also the numerous ligaments which hold the parts of each in place. Nor can the bodies of the bones remain unstrengthened; for if they have no more than the strengths needed for previous movements they will fail to bear more violent movements. Thus, saying nothing of the required changes in the pelvis, as well as in the nerves and blood-vessels, there are, counting bones, muscles, tendons, ligaments, at least fifty different parts in each hind leg which have to be enlarged. Moreover they have to be enlarged in unlike degrees. The muscles and tendons of the outer toes, for example, need not be added to so much as those of the median toes. Now, throughout their successive stages of growth, all these parts have to be kept fairly well balanced; as any one may infer on remembering sundry of the accidents he has known. Among my own friends I could name one who, when playing lawn-tennis, snapped the Achilles tendon; another who, while swinging his children, tore some of the muscular fibres in the calf of his leg; another who, in getting over a fence, tore a ligament of one knee. Such facts, joined with every one's experience of sprains, show that during the extreme exertions to which limbs are now and then subject, there is a giving way of parts not quite up to the required level of strength. How, then, is this balance to be maintained? Suppose the extensor muscles have all varied appropriately; their variations are useless unless the other co-operative parts have also varied appropriately. Worse than this. Saying nothing of the disadvantage caused by extra weight and cost of nutrition, they will be causes of mischief--causes of derangement to the rest by contracting with undue force. And then, how long will it take for the rest to be brought into adjustment? As Mr. Darwin says concerning domestic animals:--"Any particular variation would generally be lost by crossing, reversion, &c. ... unless carefully preserved by man." In a state of nature, then, favourable variations of these muscles would disappear again long before one or a few of the co-operative parts could be appropriately varied, much more before all of them could.

With this insurmountable difficulty goes a difficulty still more insurmountable--if the expression may be allowed. It is not a question of increased sizes of parts only, but of altered shapes of parts, too. A glance at the skeletons of mammals shows how unlike are the forms of the corresponding bones of their limbs; and shows that they have been severally re-moulded in each species to the different requirements entailed by its different habits. The change from the structures of hind limbs fitted only for walking and trotting to hind limbs fitted also for leaping, implies, therefore, that, along with strengthenings of bones there must go alterations in their forms. Now the fortuitous alterations of form which may take place in any bone are countless. How long, then, will it be before there takes place that particular alteration which will make the bone fitter for its new action? And what is the probability that the many required changes of shape, as well as of size, in bones will each of them be effected before all the others are lost again? If the probabilities against success are incalculable, when we take account only of changes in the sizes of parts, what shall we say of their incalculableness when differences of form also are taken into account?

"Surely this piling up of difficulties has gone far enough"; the reader will be inclined to say. By no means. There is a difficulty immeasurably transcending those named. We have thus far omitted the second half of the leap, and the provisions to be made for it. After ascent of the animal's body comes descent; and the greater the force with which it is projected up, the greater is the force with which it comes down. Hence, if the supposed creature has undergone such changes in the hind limbs as will enable them to propel it to a greater height, without having undergone any changes in the fore limbs, the result will be that on its descent the fore limbs will give way, and it will come down on its nose. The fore limbs, then, have to be changed simultaneously with the hind. How changed? Contrast the markedly bent hind limbs of a cat with its almost straight fore limbs, or contrast the silence of the spring on to the table with the thud which the fore paws make as it jumps off the table. See how unlike the actions of the hind and fore limbs are, and how unlike their structures. In what way, then, is the required co-adaptation to be effected? Even were it a question of relative sizes only, there would be no answer; for facts already given show that we may not assume simultaneous increases of size to take place in the hind and fore limbs; and, indeed, a glance at the various human races, which differ considerably in the ratios of their legs to their arms, shows us this. But it is not simply a question of sizes. To bear the increased shock of descent the fore limbs must be changed throughout in their structures. Like those in the hind limbs, the changes must be of many parts in many proportions; and they must be both in sizes and in shapes. More than this. The scapular arch and its attached muscles must also be strengthened and re-moulded. See, then, the total requirements. We must suppose that by natural selection of miscellaneous variations, the parts of the hind limbs will be co-adapted to one another, in sizes, shapes, and ratios; that those of the fore limbs will undergo co-adaptation similar in their complexity, but dissimilar in their kinds; and that the two sets of co-adaptations will be effected _pari passu_. If, as may be held, the probabilities are millions to one against the first set of changes being achieved, then it may be held that the probabilities are billions to one against the second being simultaneously achieved, in progressive adjustment to the first.

There remains only to notice the third conceivable mode of adjustment. It may be imagined that though, by the natural selection of miscellaneous variations, these adjustments cannot be effected, they may nevertheless be made to take place appropriately. How made? To suppose them so made is to suppose that the prescribed end is somewhere recognized; and that the changes are step by step simultaneously proportioned for achieving it--is to suppose a designed production of these changes. In such case, then, we have to fall back in part upon the primitive hypothesis; and if we do this in part, we may as well do it wholly--may as well avowedly return to the doctrine of special creations.

What, then, is the only defensible interpretation? If such modifications of structure produced by modifications of function as we see take place in each individual, are in any measure transmissible to descendants, then all these co-adaptations, from the simplest up to the most complex, are accounted for. In some cases this inheritance of acquired characters suffices by itself to explain the facts; and in other cases it suffices when taken in combination with the selection of favourable variations. An example of the first class is furnished by the change just considered; and an example of the second class is furnished by the case, before named, of development in a deer's horns. If, by some extra massiveness spontaneously arising, or by formation of an additional "point," an advantage is gained either for attack or defence, then, if the increased muscularity and strengthened structure of the neck and thorax, which wielding of these somewhat heavier horns produces, are in a greater or less degree inherited, and in several successive generations are by this process brought up to the required extra strength, it becomes possible and advantageous for a further increase of the horns to take place, and a further increase in the apparatus for wielding them, and so on continuously. By such processes only, in which each part gains strength in proportion to function, can co-operative parts be kept in adjustment, and be re-adjusted to meet new requirements. Close contemplation of the facts impresses me more strongly than ever with the two alternatives--either there has been inheritance of acquired characters, or there has been no evolution.

This very pronounced opinion will be met, on the part of some, by a no less pronounced demurrer, which involves a denial of possibility. It has been of late asserted, and by many believed, that inheritance of acquired characters cannot occur. Weismann, they say, has shown that there is early established in the evolution of each organism such a distinctness between those component units which carry on the individual life and those which are devoted to maintenance of the species, that changes in the one cannot affect the other. We will look closely into his doctrine.

Basing his argument on the principle of the physiological division of labour, and assuming that the primary division of labour is that between such part of an organism as carries on individual life and such part as is reserved for the production of other lives, Weismann, starting with "the first multicellular organism," says that--"Hence the single group would come to be divided into two groups of cells, which may be called somatic and reproductive--the cells of the body as opposed to those which are concerned with reproduction." (_Essays upon Heredity_, i, p. 27.)

Though he admits that this differentiation "was not at first absolute, and indeed is not always so to-day," yet he holds that the differentiation eventually becomes absolute in the sense that the somatic cells, or those which compose the body at large, come to have only a limited power of cell-division, instead of an unlimited power which the reproductive cells have; and also in the sense that eventually there ceases to be any communication between the two further than that implied by the supplying of nutriment to the reproductive cells by the somatic cells. The outcome of this argument is that, in the absence of communication, changes induced in the somatic cells, constituting the individual, cannot influence the natures of the reproductive cells, and cannot therefore be transmitted to posterity. Such is the theory. Now let us look at a few facts--some familiar, some unfamiliar.

His investigations led Pasteur to the positive conclusion that the silkworm diseases are inherited. The transmission from parent to offspring resulted, not through any contamination of the surface of the egg by the body of the parent while being deposited, but resulted from infection of the egg itself--intrusion of the parasitic organism. Generalized observations concerning the disease called _pébrine_, enabled him to decide, by inspection of the eggs, which were infected and which were not: certain modifications of form distinguishing the diseased ones. More than this; the infection was proved by microscopical examination of the contents of the egg; in proof of which he quotes as follows from Dr. Carlo Vittadini:--

"Il résulte de mes recherches sur les graines, à l'époque où commence le développement du germe, que les corpuscules, une fois apparus dans l'oeuf, augmentent graduellement en nombre, à mesure que l'embryon se développe; que, dans les derniers jours de l'incubation, l'oeuf en est plein, au point de faire croire que la majeure partie des granules du jaune se sont transformés en corpuscules.

"Une autre observation importante est que l'embryon aussi est souillé de corpuscules, et à un degré tel qu'on peut soupçonner que l'infection du jaune tire son origine du germe lui-même; en d'autres termes que le germe est primordialement infecté, et porte en lui-même ces corpuscules tout comme les vers adultes, frappés du même mal."[104]

Thus, then the substance of the egg and even its innermost vital part, is permeable by a parasite sufficiently large to be microscopically visible. It is also of course permeable by the invisible molecules of protein, out of which its living tissues are formed, and by absorption of which they subsequently grow. But, according to Weismann, it is _not_ permeable by those invisible units of protoplasm out of which the vitally active tissues of the parent are constituted: units composed, as we must assume, of variously arranged molecules of protein. So that the big thing may pass, and the little thing may pass, but the intermediate thing may not pass!

A fact of kindred nature, unhappily more familiar, may be next brought in evidence. It concerns the transmission of a disease not infrequent among those of unregulated lives. The highest authority concerning this disease, in its inherited form, is Mr. Jonathan Hutchinson; and the following are extracts from a letter I have received from him, and which I publish with his assent:--

"I do not think that there can be any reasonable doubt that a very large majority of those who suffer from inherited syphilis take the taint from the male parent.... It is the rule when a man marries who has no remaining local lesion, but in whom the taint is not eradicated, for his wife to remain apparently well, whilst her child may suffer. No doubt the child infects its mother's blood, but this does not usually evoke any obvious symptoms of syphilis.... I am sure I have seen hundreds of syphilitic infants whose mothers had not, so far as I could ascertain, ever displayed a single symptom."

See, then, to what we are committed if we accept Weismann's hypothesis. We must conclude, that whereas the reproductive cell may be effectually invaded by an abnormal living element in the parental organism, those normal living elements which constitute the vital protoplasm of the parental organism, cannot invade it. Or if it be admitted that both intrude, then the implication is that, whereas the abnormal element can so modify the development as to cause changes of structure (as of the teeth), the normal element can cause no changes of structure![105]

We pass now to evidence not much known to the world at large, but widely known in the biological world, though known in so incomplete a manner as to be undervalued in it. Indeed, when I name it, probably many will vent a mental pooh-pooh. The fact to which I refer is one of which record is preserved in the museum of the College of Surgeons, in the shape of paintings of a foal borne by a mare not quite thoroughbred, to a sire which was thoroughbred--a foal which bears the markings of the quagga. The history of this remarkable foal is given by the Earl of Morton, F.R.S., in a letter to the President of the Royal Society (read November 23, 1820). In it he states that wishing to domesticate the quagga, and having obtained a male but not a female, he made an experiment.

"I tried to breed from the male quagga and a young chestnut mare of seven-eighths Arabian blood, and which had never been bred from; the result was the production of a female hybrid, now five years old, and bearing, both in her form and in her colour, very decided indications of her mixed origin. I subsequently parted with the seven-eighths Arabian mare to Sir Gore Ouseley, who has bred from her by a very fine black Arabian horse. I yesterday morning examined the produce, namely, a two-year-old filly and a year-old colt. They have the character of the Arabian breed as decidedly as can be expected, where fifteen-sixteenths of the blood are Arabian; and they are fine specimens of that breed; but both in their colour and in the hair of their manes, they have a striking resemblance to the quagga. Their colour is bay, marked more or less like the quagga in a darker tint. Both are distinguished by the dark line along the ridge of the back, the dark stripes across the forehead, and the dark bars across the back part of the legs."[106]

Lord Morton then names sundry further correspondences. Dr. Wollaston, at that time President of the Royal Society, who had seen the animals, testified to the correctness of his description, and, as shown by his remarks, entertained no doubt about the alleged facts. But good reason for doubt may be assigned. There naturally arises the question--How does it happen that parallel results are not observed in other cases? If in any progeny certain traits not belonging to the sire, but belonging to a sire of preceding progeny, are reproduced, how is it that such anomalously inherited traits are not observed in domestic animals, and indeed in mankind? How is it that the children of a widow by a second husband do not bear traceable resemblances to the first husband? To these questions nothing like satisfactory replies seem forthcoming; and, in the absence of replies, scepticism, if not disbelief, may be held reasonable.

There is an explanation, however. Forty years ago I made acquaintance with a fact which impressed me by its significant implications, and has, for this reason I suppose, remained in my memory. It is set forth in the _Journal of the Royal Agricultural Society_, Vol. XIV (1853), pp. 214 _et seq._, and concerns certain results of crossing French and English breeds of sheep. The writer of the translated paper, M. Malingie-Nouel, Director of the Agricultural School of La Charmoise, states that when the French breeds of sheep (in which were included "the _mongrel_ Merinos") were crossed with an English breed, "the lambs present the following results. Most of them resemble the mother more than the father; some show no trace of the father." Joining the admission respecting the mongrels with the facts subsequently stated, it is tolerably clear that the cases in which the lambs bore no traces of the father were cases in which the mother was of pure breed. Speaking of the results of these crossings in the second generation, "having 75 per cent. of English blood," M. Nouel says:--"The lambs thrive, wear a beautiful appearance, and complete the joy of the breeder.... No sooner are the lambs weaned than their strength, their vigour, and their beauty begin to decay.... At last the constitution gives way ... he remains stunted for life:" the constitution being thus proved unstable or unadapted to the requirements. How, then, did M. Nouel succeed in obtaining a desirable combination of a fine English breed with the relatively poor French breeds?

He took an animal from "flocks originally sprung from a mixture of the two distinct races that are established in those two provinces [Berry and La Sologne]," and these he "united with animals of another mixed breed ... which blended the Tourangelle and native Merino blood of" La Beauce and Touraine, and obtained a mixture of all four races "without decided character, without fixity ... but possessing the advantage of being used to our climate and management."

Putting one of these "mixed blood ewes to a pure New-Kent ram ... one obtains a lamb containing fifty-hundredths of the purest and most ancient English blood, with twelve and a half hundredths of four different French races, which are individually lost in the preponderance of English blood, and disappear almost entirely, leaving the improving type in the ascendant.... All the lambs produced strikingly resembled each other, and even Englishmen took them for animals of their own country."

M. Nouel goes on to remark that when this derived breed was bred with itself, the marks of the French breeds were lost. "Some slight traces" could be detected by experts, but these "soon disappeared."

Thus we get proof that relatively pure constitutions predominate in progeny over much mixed constitutions. The reason is not difficult to see. Every organism tends to become adapted to its conditions of life; and all the structures of a species, accustomed through multitudinous generations to the climate, food, and various influences of its locality, are moulded into harmonious co-operation favourable to life in that locality: the result being that in the development of each young individual, the tendencies conspire to produce the fit organization. It is otherwise when the species is removed to a habitat of different character, or when it is of mixed breed. In the one case its organs, partially out of harmony with the requirements of its new life, become partially out of harmony with one another; since, while one influence, say of climate, is but little changed, another influence, say of food, is much changed; and, consequently, the perturbed relations of the organs interfere with their original stable equilibrium. Still more in the other case is there a disturbance in equilibrium. In a mongrel, the constitution derived from each source repeats itself as far as possible. Hence a conflict of tendencies to evolve two structures more or less unlike. The tendencies do not harmoniously conspire, but produce partially incongruous sets of organs. And evidently where the breed is one in which there are united the traits of various lines of ancestry, there results an organization so full of small incongruities of structure and action, that it has a much-diminished power of maintaining its balance; and while it cannot withstand so well adverse influences, it cannot so well hold its own in the offspring. Concerning parents of pure and mixed breeds respectively, severally tending to reproduce their own structures in progeny, we may therefore say, figuratively, that the house divided against itself cannot withstand the house of which the members are in concord.

Now if this is shown to be the case with breeds the purest of which have been adapted to their habitats and modes of life during some few hundred years only, what shall we say when the question is of a breed which has had a constant mode of life in the same locality for ten thousand years or more, like the quagga? In this the stability of constitution must be such as no domestic animal can approach. Relatively stable as may have been the constitutions of Lord Morton's horses, as compared with the constitutions of ordinary horses, yet, since Arab horses, even in their native country, have probably in the course of successive conquests and migrations of tribes become more or less mixed, and since they have been subject to the conditions of domestic life, differing much from the conditions of their original wild life, and since the English breed has undergone the perturbing effects of change from the climate and food of the East to the climate and food of the West, the organizations of the horse and mare in question could have had nothing like that perfect balance produced in the quagga by a hundred centuries of harmonious co-operation. Hence the result. And hence at the same time the interpretation of the fact that analogous phenomena are not obvious among most domestic animals, or among ourselves; since both have relatively mixed, and generally extremely mixed, constitutions, which, as we see in ourselves, have been made generation after generation, not by the formation of a mean between two parents, but by the jumbling of traits of the one with traits of the other; until there exist no such conspiring tendencies among the parts as cause repetition of combined details of structure in posterity.

Expectation that scepticism might be felt respecting this alleged anomaly presented by the quagga-marked foal, had led me to think over the matter; and I had reached this interpretation before sending to the College of Surgeons Museum (being unable to go myself) to obtain the particulars and refer to the records. When there was brought to me a copy of the account as set forth in the _Philosophical Transactions_, it was joined with the information that there existed an appended account of pigs, in which a parallel fact had been observed. To my immediate inquiry--"Was the male a wild pig?" there came the reply--"I did not observe." Of course I forthwith obtained the volume, and there found what I expected. It was contained in a paper communicated by Dr. Wollaston from Daniel Giles, Esq., concerning his "sow and her produce," which said that--

"she was one of a well-known black and white breed of Mr. Western, the Member for Essex. About ten years since I put her to a boar of the wild breed, and of a deep chestnut colour which I had just received from Hatfield House, and which was soon afterwards drowned by accident. The pigs produced (which were her first litter) partook in appearance of both boar and sow, but in some the chestnut colour of the boar strongly prevailed.

"The sow was afterwards put to a boar of Mr. Western's breed (the wild boar having been long dead). The produce was a litter of pigs, some of which, we observed with much surprise, to be stained and clearly marked with the chestnut colour which had prevailed in the former litter."

Mr. Giles adds that in a second litter of pigs, the father of which was of Mr. Western's breed, he and his bailiff believe there was a recurrence, in some, of the chestnut colour, but admits that their "recollection is much less perfect than I wish it to be." He also adds that, in the course of many years' experience, he had never known the least appearance of the chestnut colour in Mr. Western's breed.

What are the probabilities that these two anomalous results should have arisen, under these exceptional conditions, as a matter of chance? Evidently the probabilities against such a coincidence are enormous. The testimony is in both cases so good that, even apart from the coincidence, it would be unreasonable to reject it; but the coincidence makes acceptance of it imperative. There is mutual verification, at the same time that there is a joint interpretation yielded of the strange phenomenon, and of its non-occurrence under ordinary circumstances.

And now, in presence of these facts, what are we to say? Simply that they are fatal to Weismann's hypothesis. They show that there is none of the alleged independence of the reproductive cells; but that the two sets of cells are in close communion. They prove that while the reproductive cells multiply and arrange themselves during the evolution of the embryo, some of their germ-plasm passes into the mass of somatic cells constituting the parental body, and becomes a permanent component of it. Further, they necessitate the inference that this introduced germ-plasm, everywhere diffused, is some of it included in the reproductive cells subsequently formed. And if we thus get a demonstration that the somewhat different units of a foreign germ-plasm permeating the organism, permeate also the subsequently formed reproductive cells, and affect the structures of the individuals arising from them, the implication is that the like happens with those native units which have been made somewhat different by modified functions: there must be a tendency to inheritance of acquired characters.

One more step only has to be taken. It remains to ask what is the flaw in the assumption with which Weismann's theory sets out. If, as we see, the conclusions drawn from it do not correspond to the facts, then, either the reasoning is invalid, or the original postulate is untrue. Leaving aside all questions concerning the reasoning, it will suffice here to show the untruth of the postulate. Had his work been written during the early years of the cell-doctrine, the supposition that the multiplying cells of which the _Metazoa_ and _Metaphyta_ are composed, become completely separate, could not have been met by a reasonable scepticism; but now, not only is scepticism justifiable, but denial is called for. Some dozen years ago it was discovered that in many cases vegetal cells are connected with one another by threads of protoplasm--threads which unite the internal protoplasm of one cell with the internal protoplasms of cells around It is as though the pseudopodia of imprisoned rhizopods were fused with the pseudopodia of adjacent imprisoned rhizopods. We cannot reasonably suppose that the continuous network of protoplasm thus constituted has been produced after the cells have become adult. These protoplasmic connections must have survived the process of fission. The implication is that the cells forming the embryo-plant retained their protoplasmic connections while they multiplied, and that such connections continued throughout all subsequent multiplications--an implication which has, I believe, been established by researches upon germinating palm-seeds. But now we come to a verifying series of facts which the cell-structures of animals in their early stages present. In his _Monograph of the Development of Peripatus Capensis_, Mr. Adam Sedgwick, F.R.S., Reader in Animal Morphology at Cambridge, writes as follows:--

"All the cells of the ovum, ectodermal as well as endodermal, are connected together by a fine protoplasmic reticulum." (p. 41)

"The continuity of the various cells of the segmenting ovum is primary, and not secondary; _i. e._, in the cleavage the segments do not completely separate from one another. But are we justified in speaking of cells at all in this case? _The fully segmented ovum is a syncytium, and there are not and have not been at any stage cell limits._" (p. 41)

"It is becoming more and more clear every day that the cells composing the tissues of animals are not isolated units, but that they are connected with one another. I need only refer to the connection known to exist between connective tissue cells, cartilage cells, epithelial cells, &c. And not only may the cells of one tissue be continuous with each other, but they may also be continuous with the cells of other tissues." (pp. 47-8)

"Finally, if the protoplasm of the body is primitively a syncytium, and the ovum until maturity a part of that syncytium, the separation of the generative products does not differ essentially from the internal gemmation of a Protozoon, and the inheritance by the offspring of peculiarities first appearing in the parent, though not explained, is rendered less mysterious; for the protoplasm of the whole body being continuous, change in the molecular constitution of any part of it would naturally be expected to spread, in time, through the whole mass." (p. 49)

Mr. Sedgwick's subsequent investigations confirm these conclusions. In a letter of December 27, 1892, passages which he allows me to publish run as follows:--

"All the embryological studies that I have made since that to which you refer confirm me more and more in the view that the connections between the cells of adults are not secondary connections, but primary, dating from the time when the embryo was a unicellular structure.... My own investigations on this subject have been confined to the Arthropoda, Elasmobranchii, and Aves. I have thoroughly examined the development of at least one kind of each of these groups, and I have never been able to detect a stage in which the cells were not continuous with each other; and I have studied innumerable stages from the beginning of cleavage onwards."

So that the alleged independence of the reproductive cells does not exist. The _soma_--to use Weismann's name for the aggregate of cells forming the body--is, in the words of Mr. Sedgwick, "a continuous mass of vacuolated protoplasm;" and the reproductive cells are nothing more than portions of it separated some little time before they are required to perform their functions.

Thus the theory of Weismann is doubly disproved. Inductively we are shown that there _does_ take place that communication of characters from the somatic cells to the reproductive cells, which he says cannot take place; and deductively we are shown that this communication is a natural sequence of connections between the two which he ignores; his various conclusions are deduced from a postulate which is untrue.

* * * * *

From the title of this essay, and from much of its contents, nine readers out of ten will infer that it is directed against the views of Mr. Darwin. They will be astonished on being told that, contrariwise, it is directed against the views of those who, in a considerable measure, dissent from Mr. Darwin. For the inheritance of acquired characters, which it is now the fashion in the biological world to deny, was, by Mr. Darwin, fully recognized and often insisted on. Such of the foregoing arguments as touch Mr. Darwin's views, simply imply that the cause of evolution which at first he thought unimportant, but the importance of which he increasingly perceived as he grew older, is more important than he admitted, even at the last. The neo-Darwinists, however, do not admit this cause at all.

Let it not be supposed that this explanation implies any disapproval of the dissentients, considered as such. Seeing how little regard for authority I have myself usually shown, it would be absurd in me to reflect in any degree upon those who have rejected certain of Mr. Darwin's teachings, for reasons which they have held sufficient. But while their independence of thought is to be applauded rather than blamed, it is, I think, to be regretted that they have not guarded themselves against a long-standing bias. It is a common trait of human nature to seek some excuse when found in the wrong. Invaded self-esteem sets up a defence, and anything is made to serve. Thus it happened that when geologists and biologists, previously holding that all kinds of organisms arose by special creations, surrendered to the battery opened upon them by _The Origin of Species_, they sought to minimise their irrationality by pointing to irrationality on the other side. "Well, at any rate, Lamarck was in the wrong." "It is clear that we were right in rejecting _his_ doctrine." And so, by duly emphasizing the fact that he overlooked "Natural Selection" as the chief cause, and by showing how erroneous were some of his interpretations, they succeeded in mitigating the sense of their own error. It is true their creed was that at successive periods in the Earth's history, old Floras and Faunas had been abolished and others introduced; just as though, to use Professor Huxley's figure, the table had been now and again kicked over and a new pack of cards brought out. And it is true that Lamarck, while he rejected this absurd creed, assigned for the facts reasons some of which are absurd. But in consequence of the feeling described, his defensible belief was forgotten and only his indefensible ones remembered. This one-sided estimate has become traditional; so that there is now often shown a subdued contempt for those who suppose that there can be any truth in the reasonings of a man whose general conception was partly sense, at a time when the general conceptions of his contemporaries were wholly nonsense. Hence results unfair treatment--hence result the different dealings with the views of Lamarck and of Weismann.

"Where are the facts proving the inheritance of acquired characters?" ask those who deny it. Well, in the first place, there might be asked the counter-question--Where are the facts which disprove it? Surely if not only the general structures of organisms, but also many of the modifications arising in them, are inheritable, the natural implication is that all modifications are inheritable; and if any say that the inheritableness is limited to those arising in a certain way, the _onus_ lies on them of proving that those otherwise arising are not inheritable.[107] Leaving this counter-question aside, however, it will suffice if we ask another counter-question. It is asserted that the dwindling of organs from disuse is due to the successive survivals in posterity of individuals in which the organs have varied in the direction of decrease. Where now are the facts supporting this assertion? Not one has been assigned or can be assigned. Not a single case can be named in which _panmixia_ is a proved cause of diminution. Even had the deductive argument for _panmixia_ been as valid as we have found it to be invalid, there would still have been required, in pursuance of scientific method, some verifying inductive evidence. Yet, though not a shred of such evidence has been given, the doctrine is accepted with acclamation, and adopted as part of current biological theory. Articles are written and letters published in which it is assumed that this mere speculation, justified by not a tittle of proof, displaces large conclusions previously drawn. And then, passing into the outer world, this unsupported belief affects opinions there too; so that we have recently had a Right Honourable lecturer who, taking for granted its truth, represents the inheritance of acquired characters as an exploded hypothesis, and proceeds to give revised views of human affairs.

Finally, there comes the reply that there _are_ facts proving the inheritance of acquired characters. All those assigned by Mr. Darwin, together with others such, remain outstanding when we find that the interpretation by _panmixia_ is untenable. Indeed, even had that hypothesis been tenable, it would have been inapplicable to these cases; since in domestic animals, artificially fed and often overfed, the supposed advantage from economy cannot be shown to tell; and since, in these cases, individuals are not naturally selected during the struggle for life, in which certain traits are advantageous, but are artificially selected by man without regard to such traits. Should it be urged that the assigned facts are not numerous, it may be replied that there are no persons whose occupations and amusements incidentally bring out such facts; and that they are probably as numerous as those which would have been available for Mr. Darwin's hypothesis, had there been no breeders and fanciers and gardeners who, in pursuit of their profits and hobbies, furnished him with evidence. It may be added that the required facts are not likely to be numerous, if biologists refuse to seek for them.

See, then, how the case stands. Natural selection, or survival of the fittest, is almost exclusively operative throughout the vegetal world and throughout the lower animal world, characterized by relative passivity. But with the ascent to higher types of animals, its effects are in increasing degrees involved with those produced by inheritance of acquired characters; until, in animals of complex structures, inheritance of acquired characters becomes an important, if not the chief, cause of evolution. We have seen that natural selection cannot work any changes in organisms save such as conduce in considerable degrees, directly or indirectly, to the multiplication of the stirp; whence failure to account for various changes ascribed to it. And we have seen that it yields no explanation of the co-adaptation of co-operative parts, even when the co-operation is relatively simple, and still less when it is complex. On the other hand, we see that if, along with the transmission of generic and specific structures, there tend to be transmitted modifications arising in a certain way, there is a strong _a priori_ probability that there tend to be transmitted modifications arising in all ways. We have a number of facts confirming this inference, and showing that acquired characters are inherited--as large a number as can be expected, considering the difficulty of observing them and the absence of search. And then to these facts may be added the facts with which this essay set out, concerning the distribution of tactual discriminativeness. While we saw that these are inexplicable by survival of the fittest, we saw that they are clearly explicable as resulting from the inheritance of acquired characters. And here let it be added that this conclusion is conspicuously warranted by one of the methods of inductive logic, known as the method of concomitant variations. For throughout the whole series of gradations in perceptive power, we saw that the amount of the effect is proportionate to the amount of the alleged cause.

II.

Apart from those more special theories of Professor Weismann I lately dealt with, the wide acceptance of which by the biological world greatly surprises me, there are certain more general theories of his--fundamental theories--the acceptance of which surprises me still more. Of the two on which rests the vast superstructure of his speculations, the first concerns the distinction between the reproductive elements of each organism and the non-reproductive elements. He says:--

"Let us now consider how it happened that the multicellular animals and plants, which arose from unicellular forms of life, came to lose this power of living for ever.

"The answer to this question is closely bound up with the principle of division of labour which appeared among multicellular organisms at a very early stage....

"The first multicellular organism was probably a cluster of similar cells, but these units soon lost their original homogeneity. As the result of mere relative position, some of the cells were especially fitted to provide for the nutrition of the colony, while others undertook the work of reproduction." (_Essays upon Heredity_, i, p. 27)

Here, then, we have the great principle of the division of labour, which is the principle of all organization, taken as primarily illustrated in the division between the reproductive cells and the non-reproductive or somatic cells--the cells devoted to the continuance of the species, and the cells which subserve the life of the individual. And the early separation of reproductive cells from somatic cells, is alleged on the ground that this primary division of labour is that which arises between elements devoted to species-life and elements devoted to individual life. Let us not be content with words but look at the facts.

When Milne-Edwards first used the phrase "physiological division of labour," he was obviously led to do so by perceiving the analogy between the division of labour in a society, as described by political economists, and the division of labour in an organism. Every one who reads has been familiarized with the first as illustrated in the early stages, when men were warriors while the cultivation and drudgery were done by slaves and women; and as illustrated in the later stages, when not only are agriculture and manufactures carried on by separate classes, but agriculture is carried on by landlords, farmers, and labourers, while manufactures, multitudinous in their kinds, severally involve the actions of capitalists, overseers, workers, &c., and while the great function of distribution is carried on by wholesale and retail dealers in different commodities. Meanwhile students of biology, led by Milne-Edwards's phrase, have come to recognize a parallel arrangement in a living creature; shown, primarily, in the devoting of the outer parts to the general business of obtaining food and escaping from enemies, while the inner parts are devoted to the utilization of food, and supporting themselves and the outer parts; and shown, secondarily, by the subdivision of these great functions into those of various limbs and senses in the one case, and in the other case into those of organs for digestion, respiration, circulation, excretion, &c. But now let us ask what is the essential nature of this division of labour. In both cases it is an _exchange of services_--an arrangement under which, while one part devotes itself to one kind of action and yields benefits to all the rest, all the rest, jointly and severally performing their special actions, yield benefits to it in exchange. Otherwise described, it is a system of _mutual_ dependence: A depends for its welfare upon B, C, and D; B upon A, C, and D; and so with the rest: all depend upon each and each upon all. Now let us apply this true conception of the division of labour, to that which Professor Weismann calls a division of labour. Where is the _exchange of services_ between somatic cells and reproductive cells? There is none. The somatic cells render great services to the reproductive cells, by furnishing them with materials for growth and multiplication; but the reproductive cells render no services at all to the somatic cells. If we look for the _mutual_ dependence we look in vain. We find entire dependence on the one side and none on the other. Between the parts devoted to individual life and the part devoted to species-life, there is no division of labour whatever. The individual works for the species; but the species works not for the individual. Whether at the stage when the species is represented by reproductive cells, or at the stage when it is represented by eggs, or at the stage when it is represented by young, the parent does everything for it, and it does nothing for the parent. The essential part of the conception is gone: there is no giving and receiving, no exchange, no mutuality.

But now suppose we pass over this fallacious interpretation, and grant Professor Weismann his fundamental assumption and his fundamental corollary. Suppose we grant that because the primary division of labour is that between somatic cells and reproductive cells, these two groups are the first to be differentiated. Having granted this corollary, let us compare it with the facts. As the alleged primary division of labour is universal, so the alleged primary differentiation should be universal too. Let us see whether it is so. Already, in the paragraph from which I have quoted above, a crack in the doctrine is admitted: it is said that "this differentiation was not at first absolute, and indeed it is not always so to-day." And then, on turning to page 74, we find that the crack has become a chasm. Of the reproductive cells it is stated that--"In Vertebrata they do not become distinct from the other cells of the body until the embryo is completely formed." That is to say, in this large and most important division of the animal kingdom, the implied universal law does not hold. Much more than this is confessed. Lower down the page we read--"There may be in fact cases in which such separation does not take place until after the animal is completely formed, and others, as I believe that I have shown, in which it first arises one or more generations later, viz., in the buds produced by the parent."

So that in other great divisions of the animal kingdom the alleged law is broken; as among the _Coelenterata_ by the _Hydrozoa_, as among the _Mollusca_ by the Ascidians, and as among the _Platyhelminthes_ by the Trematode worms.

Following this admission concerning the _Vertebrata_, come certain sentences which I partially italicize:--

"Thus, as their development shows, a marked antithesis exists between the substance of the undying reproductive cells and that of the perishable body-cells. We cannot explain this fact except _by the supposition_ that each reproductive cell potentially contains two kinds of substance, which at a variable time after the commencement of embryonic development, separate from one another, and finally produce two sharply contrasted groups of cells." (p. 74)

And a little lower down the page we meet with the lines:--

"_It is therefore quite conceivable_ that the reproductive cells might separate from the somatic cells much later than in the examples mentioned above, without changing the hereditary tendencies of which they are the bearers."

That is to say, it is "quite conceivable" that after sexless _Cercariæ_ have gone on multiplying by internal gemmation for generations, the "two kinds of substance" have, notwithstanding innumerable cell-divisions, preserved their respective natures, and finally separate in such ways as to produce reproductive cells. Here Professor Weismann does not, as in a case before noted, assume something which it is "easy to imagine," but he assumes something which it is difficult to imagine; and apparently thinks that a scientific conclusion may be thereon safely based.

* * * * *

Associated with the assertion that the primary division of labour is between the somatic cells and the reproductive cells, and associated with the corollary that the primary differentiation is that which arises between them, there goes another corollary. It is alleged that there exists a fundamental distinction of nature between these two classes of cells. They are described as respectively mortal and immortal, in the sense that those of the one class are limited in their powers of multiplication, while those of the other class are unlimited. And it is contended that this is due to inherent unlikeness of nature.

Before inquiring into the truth of this proposition, I may fitly remark upon a preliminary proposition set down by Professor Weismann. Referring to the hypothesis that death depends "upon causes which lie in the nature of life itself," he says:--

"I do not however believe in the validity of this explanation: I consider that death is not a primary necessity, but that it has been secondarily acquired as an adaptation. I believe that life is endowed with a fixed duration, not because it is contrary to its nature to be unlimited, but because the unlimited existence of individuals would be a luxury without any corresponding advantage." (p. 24)

This last sentence has a teleological sound which would be appropriate did it come from a theologian, but which seems strange as coming from a man of science. Assuming, however, that the implication was not intended, I go on to remark that Professor Weismann has apparently overlooked a universal law of evolution--not organic only, but inorganic and super-organic--which implies the necessity of death. The changes of every aggregate, no matter of what kind, inevitably end in a state of equilibrium. Suns and planets die, as well as organisms. The process of integration, which constitutes the fundamental trait of all evolution, continues until it has brought about a state which negatives further alterations, molar or molecular--a state of balance among the forces of the aggregate and the forces which oppose them.[108] In so far, therefore, as Professor Weismann's conclusions imply the non-necessity of death, they cannot be sustained.

But now let us consider the above-described antithesis between the immortal _Protozoa_ and the mortal _Metazoa_. An essential part of the theory is that the _Protozoa_ can go on dividing and subdividing without limit, so long as the fit external conditions are maintained. But what is the evidence for this? Even by Professor Weismann's own admission there is no proof. On p. 285 he says:--

"I could only consent to adopt the hypothesis of rejuvenescence [achieved by conjugation], if it were rendered absolutely certain that reproduction by division could never under any circumstances persist indefinitely. But this cannot be proved with any greater certainty than the converse proposition, and hence, as far as direct proof is concerned, the facts are equally uncertain on both sides."

But this is an admission which seems to be entirely ignored when there is alleged the contrast between the immortal _Protozoa_ and the mortal _Metazoa_. Following Professor Weismann's method, it would be "easy to imagine" that occasional conjugation is in all cases essential; and this easily imagined conclusion might fitly be used to bar out his own. Indeed, considering how commonly conjugation is observed, it may be held difficult to imagine that it can in any cases be dispensed with. Apart from imaginations of either kind, however, here is an acknowledgment that the immortality of _Protozoa_ is not proved; that the allegation has no better basis than the failure to observe cessation of fission; and that thus one term of the above antithesis is not a fact, but is only an assumption.

And now what about the other term of the antithesis--the alleged inherent mortality of the somatic cells? This we shall, I think, find is no more defensible than the other. Such plausibility as it possesses disappears when, instead of contemplating the vast assemblage of familiar cases which animals present, we contemplate certain less familiar and unfamiliar cases. By these we are shown that the usual ending of multiplication among somatic cells is due, not to an intrinsic cause, but to extrinsic causes. Let us, however, first look at Professor Weismann's own statements:--

"I have endeavoured to explain death as the result of restriction in the powers of reproduction possessed by the somatic cells, and I have suggested that such restriction may conceivably follow from a limitation in the number of cell-generations possible for the cells of each organ and tissue." (p. 28)

"The above-mentioned considerations show us that the degree of reproductive activity present in the tissues is regulated by internal causes while the natural death of an organism is the termination--the hereditary limitation--of the process of cell-division, which began in the segmentation of the ovum." (p. 30)

Now, though, in the above extracts there is mention of "internal causes" determining "the degree of reproductive activity" of tissue cells, and though, on page 28, the "causes of the loss" of the power of unlimited cell-production "must be sought outside the organism, that is to say, in the external conditions of life," yet the doctrine is that somatic cells have become constitutionally unfitted for continued cell-multiplication.

"The somatic cells have lost this power to a gradually increasing extent, so that at length they became restricted to a fixed, though perhaps very large, number of cell-generations." (p. 28)

Examination will soon disclose good reasons for denying this inherent restriction. We will look at the various causes which affect their multiplication, and usually put a stop to increase after a certain point is reached.

There is first the amount of vital capital given by the parent; partly in the shape of a more or less developed structure, and partly in the shape of bequeathed nutriment. Where this vital capital is small, and the young creature, forthwith obliged to carry on physiological business for itself, has to expend effort in obtaining materials for daily consumption as well as for growth, a rigid restraint is put on that cell-multiplication required for a large size. Clearly, the young elephant, starting with a big and well-organized body, and supplied _gratis_ with milk during early stages of growth, can begin physiological business on his own account on a great scale; and by its large transactions his system is enabled to supply nutriment to its multiplying somatic cells until they have formed a vast aggregate--an aggregate such as it is impossible for a young mouse to reach, obliged as it is to begin physiological business in a small way. Then there is the character of the food in respect of its digestibility and its nutritiveness. Here, that which the creature takes in requires much grinding-up, or, when duly prepared, contains but a small amount of available matter in comparison with the matter that has to be thrown away; while there, the prey seized is almost pure nutriment, and requires but little trituration. Hence, in some cases, an unprofitable physiological business, and in other cases a profitable one; resulting in small or large supplies to the multiplying somatic cells. Further, there has to be noted the grade of visceral development, which, if low, yields only crude nutriment slowly distributed, but which, if high, serves by its good appliances for solution, depuration, absorption, and circulation, to yield to the multiplying somatic cells a rich and pure blood. Then we come to an all-important factor, the cost of obtaining food. Here large expenditure of energy in locomotion is necessitated, and there but little--here great efforts for small portions of food, and there small efforts for great portions: again resulting in physiological poverty or physiological wealth. Next, beyond the cost of nervo-muscular activities in foraging, there is the cost of maintaining bodily heat. So much heat implies so much consumed nutriment, and the loss by radiation or conduction, which has perpetually to be made good, varies according to many circumstances--climate, medium (as air or water), covering, size of body (small cooling relatively faster than large); and in proportion to the cost of maintaining heat is the abstraction from the supplies for cell-formation. Finally, there are three all-important co-operative factors, or rather laws of factors, the effects of which vary with the size of the animal. The first is that, while the mass of the body varies as the cubes of its dimensions (_proportions_ being supposed constant), the absorbing surface varies as the squares of its dimensions; whence it results that, other things equal, increase of size implies relative decrease of nutrition, and therefore increased obstacles to cell-multiplication.[109] The second is a further sequence from these laws--namely, that while the weight of the body increases as the cubes of the dimensions, the sectional areas of its muscles and bones increase as their squares; whence follows a decreasing power of resisting strains, and a relative weakness of structure. This is implied in the ability of a small animal to leap many times its own length, while a great animal, like the elephant, cannot leap at all: its bones and muscles being unable to bear the stress which would be required to propel its body through the air. What increasing cost of keeping together the bodily fabric is thus entailed, we cannot say; but that there is an increasing cost, which diminishes the available, materials for increase of size, is beyond question.[110] And then, in the third place, we have augmented expense of distribution of nutriment. The greater the size becomes, the more force must be exerted to send blood to the periphery; and this once more entails deduction from the cell-forming matters.

Here, then, we have nine factors, several of them involving subdivisions, which co-operate in aiding or restraining cell-multiplication. They occur in endlessly varied proportions and combinations; so that every species differs more or less from every other in respect of their effects. But in all of them the co-operation is such as eventually arrests that multiplication of cells which causes further growth; continues thereafter to entail slow decrease in cell-multiplication, accompanying decline of vital activities; and eventually brings cell-multiplication to an end. Now a recognized principle of reasoning--the Law of Parsimony--forbids the assumption of more causes than are needful for explanation of phenomena; and since, in all such living aggregates as those above supposed, the causes named inevitably bring about arrest of cell-multiplication, it is illegitimate to ascribe this arrest to some inherent property in the cells. Inadequacy of the other causes must be shown before an inherent property can be rightly assumed.

For this conclusion we find ample justification when we contemplate types of animals which lead lives that do not put such decided restraints on cell-multiplication. First let us take an instance of the extent to which (irrespective of natures of cells as reproductive or somatic) cell-multiplication may go, where the conditions render nutrition easy and reduce expenditure to a minimum. I refer to the case of the _Aphides_. Though it is early in the season (March), the hothouses at Kew have furnished a sufficient number of these to show that twelve of them weigh a grain--a larger number than would be required were they full-sized. Citing Professor Owen, who adopts the calculations of Tougard to the effect that by agamic multiplication "a single impregnated ovum of _Aphis_ may give rise, without fecundation, to a quintillion of _Aphides_," Professor Huxley says:--

"I will assume that an Aphis weighs 1/1000 of a grain, which is certainly vastly under the mark. A quintillion of _Aphides_ will, on this estimate, weigh a quatrillion of grains. He is a very stout man who weighs two million grains; consequently the tenth brood alone, if all its members survive the perils to which they are exposed, contains more substance than 500,000,000 stout men--to say the least, more than the whole population of China!"[111]

And had Professor Huxley taken the actual weight, one-twelfth of a grain, the quintillion of _Aphides_ would evidently far outweigh the whole human population of the globe: five billions of tons being the weight, as brought out by my own calculation! Of course I do not cite this in proof of the extent to which multiplication of somatic cells, descending from a single ovum, may go; because it will be contended, with some reason, that each of the sexless _Aphides_, viviparously produced, arose by fission of a cell which had descended from the original reproductive cell. I cite it merely to show that when the cell-products of a fertilized ovum are perpetually divided and subdivided into small groups, distributed over an unlimited nutritive area, so that they can get materials for growth at no cost, and expend nothing appreciable in motion or maintenance of temperature, cell-production may go on without limit. For the agamic multiplication of _Aphides_ has been shown to continue for four years, and to all appearance would be ceaseless were the temperature and supply of food continued without break. But now let us pass to analogous illustrations of cause and consequence, open to no criticism of the kind just indicated. They are furnished by various kinds of _Entozoa_, of which take the _Trematoda_, infesting molluscs and fishes. Of one of them we read:--"_Gyrodactylus_ multiplies agamically by the development of a young Trematode within the body, as a sort of internal bud. A second generation appears within the first, and even a third within the second, before the young _Gyrodactylus_ is born."[112] And the drawings of Steenstrup, in his _Alternation of Generations_, show us, among creatures of this group, a sexless individual the whole interior of which is transformed into smaller sexless individuals, which severally, before or after their emergence, undergo similar transformations--a multiplication of somatic cells without any sign of reproductive cells. Under what circumstances do such modes of agamic multiplication, variously modified among parasites, occur? They occur where there is no expenditure whatever in motion or maintenance of temperature, and where nutriment surrounds the body on all sides. Other instances are furnished by groups in which, though the nutriment is not abundant, the cost of living is almost unappreciable. Among the _Coelenterata_ there are the Hydroid Polyps, simple and compound; and among the _Mollusca_ we have various types of Ascidians, fixed and floating, _Botryllidæ_ and _Salpæ_.

But now from these low animals in which sexless reproduction, and continued multiplication of somatic cells, is common, and one class of which is named "zoophytes," because its form of life simulates that of plants, let us pass to plants themselves. In these there is no expenditure in effort, there is no expenditure in maintaining temperature, and the food, some of it supplied by the earth, is the rest of it supplied by a medium which everywhere bathes the outer surface: the utilization of its contained material being effected _gratis_ by the Sun's rays. Just as was to be expected, we here find that agamogenesis may go on without end. Numerous plants and trees are propagated to an unlimited extent by cuttings and buds; and we have sundry plants which cannot be otherwise propagated. The most familiar are the double roses of our gardens: these do not seed, and yet have been distributed everywhere by grafts and buds. Hothouses furnish many cases, as I learn from an authority second to none. Of "the whole host of tropical orchids, for instance, not one per cent. has ever seeded, and some have been a century under cultivation." Again, we have the _Acorus calamus_, "that has hardly been known to seed anywhere, though it is found wild all over the north temperate hemisphere." And then there is the conspicuous and conclusive case of _Eloidea Canadensis_ (alias _Anacharis_,) introduced no one knows how (probably with timber), and first observed in 1847, in several places; and which, having since spread over nearly all England, now everywhere infests ponds, canals, and slow rivers. The plant is dioecious, and only the female exists here. Beyond all question, therefore, this vast progeny of the first slip or fragment introduced, sufficient to cover many square miles were it put together, is constituted entirely of somatic cells. Hence, as far as we can judge, these somatic cells are immortal in the sense given to the word by Professor Weismann; and the evidence that they are so is immeasurably stronger than the evidence which leads him to assert immortality for the fissiparously-multiplying _Protozoa_. This endless multiplication of somatic cells has been going on under the eyes of numerous observers for forty odd years. What observer has watched for forty years to see whether the fissiparous multiplication of _Protozoa_ does not cease? What observer has watched for one year, or one month, or one week?[113]

Even were not Professor Weismann's theory disposed of by this evidence, it might be disposed of by a critical examination of his own evidence, using his own tests. Clearly, if we are to measure relative mortalities, we must assume the conditions to be the same and must use the same measure. Let us do this with some appropriate animal--say Man, as the most open to observation. The mortality of the somatic cells constituting the mass of the human body, is, according to Professor Weismann, shown by the decline and final cessation of cell-multiplication in its various organs. Suppose we apply this test to all the organs: not to those only in which there continually arise bile-cells, epithelium-cells, &c., but to those also in which there arise reproductive cells. What do we find? That the multiplication of these last comes to an end long before the multiplication of the first. In a healthy woman, the cells which constitute the various active tissues of the body, continue to grow and multiply for many years after germ-cells have died out. If similarly measured, then, these cells of the last class prove to be more mortal than those of the first. But Professor Weismann uses a different measure for the two classes of cells. Passing over the illegitimacy of this proceeding, let us accept his other mode of measurement, and see what comes of it. As described by him, absence of death among the _Protozoa_ is implied by that unceasing division and subdivision of which they are said to be capable. Fission continued without end, is the definition of the immortality he speaks of. Apply this conception to the reproductive cells in a _Metazoon_. That the immense majority of them do not multiply without end, we have already seen: with very rare exceptions they die and disappear without result, and they cease their multiplication while the body as a whole still lives. But what of those extremely exceptional ones which, as being actually instrumental to the maintenance of the species, are alone contemplated by Professor Weismann? Do these continue their fissiparous multiplications without end? By no means. The condition under which alone they preserve a qualified form of existence, is that, instead of one becoming two, two become one. A member of series A and a member of series B, coalesce; and so lose their individualities. Now, obviously, if the immortality of a series is shown if its members divide and subdivide perpetually, then the opposite of immortality is shown when, instead of division, there is union. Each series ends, and there is initiated a new series, differing more or less from both. Thus the assertion that the reproductive cells are immortal, can be defended only by changing the conception of immortality otherwise implied.

Even apart from these last criticisms, however, we have clear disproof of the alleged inherent difference between the two classes of cells. Among animals, the multiplication of somatic cells is brought to an end by sundry restraining conditions; but in various plants, where these restraining conditions are absent, the multiplication is unlimited. It may, indeed, be said that the alleged distinction should be reversed; since the fissiparous multiplication of reproductive cells is necessarily interrupted from time to time by coalescence, while that of the somatic cells may go on for a century without being interrupted.

* * * * *

In the essay to which this is a postscript, conclusions were drawn from the remarkable case of the horse and the quagga, there narrated, along with an analogous case observed among pigs. These conclusions have since been confirmed. I am much indebted to a distinguished correspondent who has drawn my attention to verifying facts furnished by the offspring of whites and negroes in the United States. Referring to information given him many years ago, he says:--"It was to the effect that the children of white women by a white father, had been _repeatedly_ observed to show traces of black blood, in cases when the woman had previous connection with [_i. e._ a child by] a negro." At the time I received this information, an American was visiting me; and, on being appealed to, answered that in the United States there was an established belief to this effect. Not wishing, however, to depend upon hearsay, I at once wrote to America to make inquiries. Professor Cope of Philadelphia has written to friends in the South, but has not yet sent me the results. Professor Marsh, the distinguished palæontologist, of Yale, New Haven, who is also collecting evidence, sends a preliminary letter in which he says:--"I do not myself know of such a case, but have heard many statements that make their existence probable. One instance, in Connecticut, is vouched for so strongly by an acquaintance of mine, that I have good reason to believe it to be authentic."

That cases of the kind should not be frequently seen in the North, especially nowadays, is of course to be expected. The first of the above quotations refers to facts observed in the South during slavery days; and even then, the implied conditions were naturally very infrequent. Dr. W. J. Youmans of New York has, on my behalf, interviewed several medical professors, who, though they have not themselves met with instances, say that the alleged result, described above, "is generally accepted as a fact." But he gives me what I think must be regarded as authoritative testimony. It is a quotation from the standard work of Professor Austin Flint, and runs as follows:--

"A peculiar and, it seems to me, an inexplicable fact is, that previous pregnancies have an influence upon offspring. This is well known to breeders of animals. If pure-blooded mares or bitches have been once covered by an inferior male, in subsequent fecundations the young are likely to partake of the character of the first male, even if they be afterwards bred with males of unimpeachable pedigree. What the mechanism of the influence of the first conception is, it is impossible to say; but the fact is incontestable. The same influence is observed in the human subject. A woman may have, by a second husband, children who resemble a former husband, and this is particularly well marked in certain instances by the colour of the hair and eyes. A white woman who has had children by a negro may subsequently bear children to a white man, these children presenting some of the unmistakable peculiarities of the negro race."[114]

Dr. Youmans called on Professor Flint, who remembered "investigating the subject at the time his larger work was written [the above is from an abridgment], and said that he had never heard the statement questioned."

Some days before I received this letter and its contained quotation, the remembrance of a remark I heard many years ago concerning dogs, led to the inquiry whether they furnished analogous evidence. It occurred to me that a friend who is frequently appointed judge of animals at agricultural shows, Mr. Fookes, of Fairfield, Pewsey, Wiltshire, might know something about the matter. A letter to him brought various confirmatory statements. From one "who had bred dogs for many years" he learnt that--

"It is a well known and admitted fact that if a bitch has two litters by two different dogs, the character of the first father is sure to be perpetuated in any litters she may afterwards have, no matter how pure-bred a dog may be the begetter."

After citing this testimony, Mr. Fookes goes on to give illustrations known to himself.

"A friend of mine near this had a very valuable Dachshund bitch, which most unfortunately had a litter by a stray sheep-dog. The next year her owner sent her on a visit to a pure Dachshund dog, but the produce took quite as much of the first father as the second, and the next year he sent her to another Dachshund with the same result. Another case:--A friend of mine in Devizes had a litter of puppies, unsought for, by a setter from a favourite pointer bitch, and after this she never bred any true pointers, no matter of what the paternity was."

[Since the publication of this article additional evidences have come to hand. One is from the late Prof. Riley, State Entomologist at Washington, who says that telegony is an "established principle among well-educated farmers" in the United States, and who gives me a case in horse-breeding to which he was himself witness.

Mr. W. P. Smith, writing from Stoughton Grange, Guildford, but giving the results of his experiences in America, says that "the fact of a previous conception influencing subsequent offspring was so far recognised among American cattle-breeders" that it was proposed to raise the rank of any heifer that had borne a first calf by a thoroughbred bull, and though this resolution when brought before one of the chief societies was not carried, yet on all sides it was admitted that previous conceptions had effects of the kind alleged. Mr. Smith in another letter says:--"When I had a large mule and horse ranche in America I noticed that the foals of mares by horse stallions had a mulish appearance in those cases where the mare had previously given birth to a mule foal. Common heifers who have had calves by a thoroughbred bull are apt thereafter to have well-bred calves even from the veriest scrubs."

Yet another very interesting piece of evidence is furnished by Mr. W. Sedgwick, M.R.C.S., in an article on "The Influence of Heredity in Disease," published in the _British Medical Journal_ for Feb. 22, 1896, pp. 460-2. It concerns the transmission of a malformation known among medical men as hypospadias. Referring to a man belonging to a family in which this defect prevailed, he writes:--"The widow of the man from whom these three generations of hypospadians were descended married again, after an interval of eighteen months; and in this instance the second husband was not only free from the defect, but there was no history of it in his family. By this second marriage she had four hypospadiac sons and four hypospadiac grandsons; whilst there were seven grandsons and three great-grandsons who were not malformed."]

Coming from remote places, from those who have no theory to support, and who are some of them astonished by the unexpected phenomena, the agreement dissipates all doubt. In four kinds of mammals, widely divergent in their natures--man, horse, dog, and pig--we have this same seemingly-anomalous kind of heredity, made visible under analogous conditions. We must take it as a demonstrated fact that, during gestation, traits of constitution inherited from the father produce effects upon the constitution of the mother; and that these communicated effects are transmitted by her to subsequent offspring. We are supplied with an absolute disproof of Professor Weismann's doctrine that the reproductive cells are independent of, and uninfluenced by, the somatic cells; and there disappears absolutely the alleged obstacle to the transmission of acquired characters.

* * * * *

Notwithstanding experiences showing the futility of controversy for the establishment of truth, I am tempted here to answer opponents at some length. But even could the editor allow me the needful space, I should be compelled, both by lack of time and by ill-health, to be brief. I must content myself with noticing a few points which most nearly concern me.

Referring to my argument respecting tactual discriminativeness, Mr. Wallace thinks that I--

"afford a glaring example of taking the unessential in place of the essential, and drawing conclusions from a partial and altogether insufficient survey of the phenomena. For this 'tactual discriminativeness,' which is alone dealt with by Mr. Spencer, forms the least important, and probably only an incidental portion of the great vital phenomenon of skin-sensitiveness, which is at once the watchman and the shield of the organism against imminent external dangers." (_Fortnightly Review_, April, 1893, p. 497)

Here Mr. Wallace assumes it to be self-evident that skin-sensitiveness is due to natural selection, and assumes that this must be admitted by me. He supposes it is only the unequal distribution of skin-discriminativeness which I contend is not thus accounted for. But I deny that either the general sensitiveness or the special sensitiveness results from natural selection; and I have years ago justified the first disbelief as I have recently the second. In "The Factors of Organic Evolution" (_Essays_, 454-8), I have given various reasons for inferring that the genesis of the nervous system cannot be due to survival of the fittest; but that it is due to the direct effects of converse between the surface and the environment; and that thus only is to be explained the strange fact that the nervous centres are originally superficial, and migrate inwards during development. These conclusions I have, in the essay Mr. Wallace criticizes, upheld by the evidence which blind boys and skilled compositors furnish; proving, as this does, that increased nervous development is peripherally initiated. Mr. Wallace's belief that skin-sensitiveness arose by natural selection, is unsupported by a single fact. He assumes that it _must_ have been so produced because it is all-important to self-preservation. My belief that it is directly initiated by converse with the environment, is supported by facts; and I have given proof that the assigned cause is now in operation. Am I called upon to abandon my own supported belief and accept Mr. Wallace's unsupported belief? I think not.

Referring to my argument concerning blind cave-animals, Professor Lankester, in _Nature_ of February 23, 1893, writes:--

"Mr. Spencer shows that the saving of ponderable material in the suppression of an eye is but a small economy: he loses sight of the fact, however, that possibly, or even probably, the saving to the organism in the reduction of an eye to a rudimentary state is not to be measured by mere bulk, but by the non-expenditure of special materials and special activities which are concerned in the production of an organ so peculiar and elaborate as is the vertebrate eye."

It seems to me that a supposition is here made to do duty as a fact; and that I might with equal propriety say that "possibly, or even probably," the vertebrate eye is physiologically cheap: its optical part, constituting nearly its whole bulk, consisting of a low order of tissue. There is, indeed, strong reason for considering it physiologically cheap. If any one remembers how relatively enormous are the eyes of a fish just out of the egg--a pair of eyes with a body and head attached; and if he then remembers that every egg contains material for such a pair of eyes; he will see that eye-material constitutes a very considerable part of the fish's roe; and that, since the female fish provides this quantity every year, it cannot be expensive. My argument against Weismann is strengthened rather than weakened by contemplation of these facts.

Professor Lankester asks my attention to a hypothesis of his own, published in the _Encyclopædia Britannica_, concerning the production of blind cave-animals. He thinks it can--

"be fully explained by natural selection acting on congenital fortuitous variations. Many animals are thus born with distorted or defective eyes whose parents have not had their eyes submitted to any peculiar conditions. Supposing a number of some species of Arthropod or Fish to be swept into a cavern or to be carried from less to greater depths in the sea, those individuals with perfect eyes would follow the glimmer of light and eventually escape to the outer air or the shallower depths, leaving behind those with imperfect eyes to breed in the dark place. A natural selection would thus be effected" in successive generations.

First of all, I demur to the words "many animals." Under the abnormal conditions of domestication, congenitally defective eyes may be not very uncommon; but their occurrence under natural conditions is, I fancy, extremely rare. Supposing, however, that in a shoal of young fish, there occur some with eyes seriously defective. What will happen? Vision is all-important to the young fish, both for obtaining food and for escaping from enemies. This is implied by the immense development of eyes just referred to; and the obvious conclusion to be drawn is that the partially blind would disappear. Considering that out of the enormous number of young fish hatched with perfect eyes, not one in a hundred reaches maturity, what chance of surviving would there be for those with imperfect eyes? Inevitably they would be starved or be snapped up. Hence the chances that a matured or partially matured semi-blind fish, or rather two such, male and female, would be swept into a cave and left behind are extremely remote. Still more remote must the chances be in the case of cray-fish. Sheltering themselves as these do under stones, in crevices, and in burrows which they make in the banks, and able quickly to anchor themselves to weeds or sticks by their claws, it seems scarcely supposable that any of them could be carried into a cave by a flood. What, then, is the probability that there will be two nearly blind ones, and that these will be thus carried? Then, after this first extreme improbability, there comes a second, which we may, I think, rather call an impossibility. How would it be possible for creatures subject to so violent a change of habitat to survive? Surely death would quickly follow the subjection to such utterly unlike conditions and modes of life. The existence of these blind cave-animals can be accounted for only by supposing that their remote ancestors began making excursions into the cave, and, finding it profitable, extended them, generation after generation, further in: undergoing the required adaptations little by little.[115]

Between Dr. Romanes and myself the first difference concerns the interpretation of "Panmixia." Clearer conceptions of these matters would be reached if, instead of thinking in abstract terms, the physiological processes concerned were brought into the foreground. Beyond the production of changes in the sizes of parts by the selection of fortuitously-arising variations, I can see but one other cause for the production of them--the competition among the parts for nutriment. This has the effect that active parts are well-supplied and grow, while inactive parts are ill-supplied and dwindle.[116] This competition is the cause of "economy of growth"; this is the cause of decrease from disuse; and this is the only conceivable cause of that decrease which Dr. Romanes contends follows the cessation of selection. The three things are aspects of the same thing. And now, before leaving this question, let me remark on the strange proposition which has to be defended by those who deny the dwindling of organs from disuse. Their proposition amounts to this:--that for a hundred generations an inactive organ may be partially denuded of blood all through life, and yet in the hundredth generation will be produced of just the same size as in the first!

There is one other passage in Dr. Romanes' criticism--that concerning the influence of a previous sire on progeny--which calls for comment. He sets down what he supposes Weismann will say in response to my argument. "First, he may question the fact." Well, after the additional evidence given above, I think he is not likely to do that; unless, indeed, it be that along with readiness to base conclusions on things "it is easy to imagine" there goes reluctance to accept testimony which it is difficult to doubt. Second, he is supposed to reply that "the Germ-plasm of the first sire has in some way or another become partly commingled with that of the immature ova"; and Dr. Romanes goes on to describe how there may be millions of spermatozoa and "thousands of millions" of their contained "ids" around the ovaries, to which these secondary effects are due. But, on the one hand, he does not explain why in such cases each subsequent ovum, as it becomes matured, is not fertilized by the sperm-cells present, or their contained germ-plasm, rendering all subsequent fecundations needless; and, on the other hand, he does not explain why, if this does not happen, the potency of this remaining germ-plasm is nevertheless such as to affect not only the next succeeding offspring, but all subsequent offspring. The irreconcilability of these two implications would, I think, sufficiently dispose of the supposition, even had we not daily multitudinous proofs that the surface of a mammalian ovarium is not a spermatheca. The third reply Dr. Romanes urges, is the inconceivability of the process by which the germ-plasm of a preceding male parent affects the constitution of the female and her subsequent offspring. In response, I have to ask why he piles up a mountain of difficulties based on the assumption that Mr. Darwin's explanation of heredity by "Pangenesis" is the only available explanation preceding that of Weismann? and why he presents these difficulties to me, more especially; deliberately ignoring my own hypothesis of physiological units? It cannot be that he is ignorant of this hypothesis, since the work in which it is variously set forth (_Principles of Biology_, §§ 66-97) is one with which he is well acquainted: witness his _Scientific Evidences of Organic Evolution_; and he has had recent reminders of it in Weismann's _Germ-plasm_, where it is repeatedly referred to. Why, then, does he assume that I abandon my own hypothesis and adopt that of Darwin; thereby entangling myself in difficulties which my own hypothesis avoids? If, as I have argued, the germ-plasm consists of substantially similar units (having only those minute differences expressive of individual and ancestral differences of structure), none of the complicated requirements which Dr. Romanes emphasizes exist; and the alleged inconceivability disappears.

Here I must end: not intending to say more, unless for some very urgent reason; and leaving others to carry on the discussion. I have, indeed, been led to suspend for a short time my proper work, only by consciousness of the transcendent importance of the question at issue. As I have before contended, a right answer to the question whether acquired characters are or are not inherited, underlies right beliefs, not only in Biology and Psychology, but also in Education, Ethics, and Politics.

III.

As a species of literature, controversy is characterised by a terrible fertility. Each proposition becomes the parent of half a dozen; so that a few replies and rejoinders produce an unmanageable population of issues, old and new, which end in being a nuisance to everybody. Remembering this, I shall refrain from dealing with all the points of Professor Weismann's answer. I must limit myself to a part; and that there may be no suspicion of a selection convenient to myself, I will take those contained in his first article.

Before dealing with his special arguments, let me say something about the general mode of argument which Professor Weismann adopts.

The title of his article is "The All-Sufficiency of Natural Selection."[117] Very soon, however, as on p. 322, we come to the admission, which he has himself italicised, "that _it is really very difficult to imagine this process of natural selection in its details_; and to this day it is impossible to demonstrate it in any one point." Elsewhere, as on pp. 327 and 336 _à propos_ of other cases, there are like admissions. But now if the sufficiency of an assigned cause cannot in any case be demonstrated, and if it is "really very difficult to imagine" in what way it has produced its alleged effects, what becomes of the "all-sufficiency" of the cause? How can its all-sufficiency be alleged when its action can neither be demonstrated nor easily imagined? Evidently to fit Professor Weismann's argument the title of the article should have been "The Doubtful Sufficiency of Natural Selection."

Observe, again, how entirely opposite are the ways in which he treats his own interpretation and the antagonist interpretation. He takes the problem presented by certain beautifully adapted structures on the anterior legs of "very many insects," which they use for cleansing their antennæ. These, he argues, cannot have resulted from the inheritance of acquired characters; since any supposed changes produced by function would be changes in the chitinous exo-skeleton, which, being a dead substance, cannot have had its changes transmitted. He then proceeds, very candidly, to point out the extreme difficulties which lie in the way of supposing these structures to have resulted from natural selection: admitting that an opponent might "say that it was absurd" to assume that the successive small variations implied were severally life-saving in their effects. Nevertheless, he holds it unquestionable that natural selection has been the cause. See then the difference. The supposition that the apparatus has been produced by the inheritance of acquired characters is rejected _because_ it presents insuperable difficulties. But the supposition that the apparatus has been produced by natural selection is accepted, _though_ it presents insuperable difficulties. If this mode of reasoning is allowable, no fair comparison between diverse hypotheses can be made.

With these remarks on Professor Weismann's method at large, let me now pass to the particular arguments he uses, taking them _seriatim_.

* * * * *

The first case he deals with is that of the progressive degradation of the human little toe. This he considers a good test case; and he proceeds to discuss an assigned cause--the inherited and accumulated effects of boot-pressure. Without much difficulty he shows that this interpretation is inadequate; since fusion of the phalanges, which constitutes in part the progressive degradation, is found among peoples who go barefoot, and has been found also in Egyptian mummies. Having thus disposed of Mr. Buckman's interpretation, Professor Weismann forthwith concludes that the ascription of this anatomical change to the inheritance of acquired characters is disposed of, and assumes, as the only other possible interpretation, a dwindling "through panmixia": "the hereditary degeneration of the little toe is thus quite simply explained from my standpoint."

It is surprising that Professor Weismann should not have seen that there is an explanation against which his criticism does not tell. If we go back to the genesis of the human type from some lower type of _primates_, we see that while the little toe has ceased to be of any use for climbing purposes, it has not come into any considerable use for walking and running. A glance at the feet of the sub-human _primates_ in general, shows that the inner digits are, as compared with those of men, quite small, have no such relative length and massiveness as the human great toes. Leaving out the question of cause, it is manifest that the great toes have been immensely developed, since there took place the change from arboreal habits to terrestrial habits. A study of the mechanics of walking shows why this has happened. Stability requires that the "line of direction" (the vertical line let fall from the centre of gravity) shall fall within the base, and, in walking, shall be brought at each step within the area of support, or so near it that any tendency to fall may be checked at the next step. A necessary result is that if, at each step, the chief stress of support is thrown on the outer side of the foot, the body must be swayed so that the "line of direction" may fall within the outer side of the foot, or close to it; and when the next step is taken it must be similarly swayed in an opposite way, so that the outer side of the other foot may bear the weight. That is to say, the body must oscillate from side to side, or waddle. The movements of a duck when walking or running show what happens when the points of support are wide apart. Clearly this kind of movement conflicts with efficient locomotion. There is a waste of muscular energy in making these lateral movements, and they are at variance with the forward movement. We may infer, then, that the developing man profited by throwing the stress as much as possible on the inner sides of the feet; and was especially led to do this when going fast, which enabled him to abridge the oscillations: as indeed we now see in a drunken man. Thus there was thrown a continually increasing stress upon the inner digits as they progressively developed from the effects of use; until now that the inner digits, so large compared with the others, bear the greater part of the weight, and being relatively near one another, render needless any marked swayings from side to side. But what has meanwhile happened to the outer digits? Evidently as fast as the great toes have come more and more into play and developed, the little toes have gone more and more out of play and have been dwindling for--how long shall we say?--perhaps a hundred thousand years.

So far, then, am I from feeling that Professor Weismann has here raised a difficulty in the way of the doctrine I hold, that I feel indebted to him for having drawn attention to a very strong evidence in its support. This modification in the form of the foot, which has occurred since arboreal habits have given place to terrestrial habits, shows the effects of use and disuse simultaneously. The inner digits have increased by use while the outer digits have decreased by disuse.

* * * * *

Saying that he will not "pause to refute other apparent proofs of the transmission of acquired characters," Professor Weismann proceeds to deal with the argument which, with various illustrations, I have several times urged--the argument that the natural selection of fortuitously-arising variations cannot account for the adjustment of co-operative parts. Very clearly and very fairly he summarises this argument as used in _The Principles of Biology_ in 1864. Admitting that in this case there are "enormous difficulties" in the way of any other interpretation than the inheritance of acquired characters, Professor Weismann before proceeding to assault this "last bulwark of the Lamarckian principle," premises that the inheritance of acquired characters cannot be a cause of change because inactive as well as active parts degenerate when they cease to be of use: instancing the "skin and skin-armature of crabs and insects." On this I may remark in the first place that an argument derived from degeneracy of passive structures scarcely meets the case of development of active structures; and I may remark in the second place that I have never dreamt of denying the efficiency of natural selection as a cause of degeneracy in passive structures when the degeneracy is such as aids the prosperity of the stirp.

Making this parenthetical reply to his parenthetical criticism I pass to his discussion of this particular argument which he undertakes to dispose of.

His _cheval de bataille_ is furnished him by the social insects--not a fresh one, however, as might be supposed from the way in which he mounts it. From time to time it has carried other riders, who have couched their lances with fatal effects as they supposed. But I hope to show that no one of them has unhorsed an antagonist, and that Professor Weismann fails to do this just as completely as his predecessors. I am, indeed, not sorry that he has afforded me the opportunity of criticising the general discussion concerning the peculiarities of these interesting creatures, which it has often seemed to me sets out with illegitimate assumptions. The supposition always is that the specialities of structures and instincts in the unlike classes of their communities, have arisen during the period in which the communities have existed in something like their present forms. This cannot be. It is doubtless true that association without differentiations of classes may pre-exist for co-operative purposes, as among wolves, and as among various insects which swarm under certain circumstances. Hence we may suppose that there arise in some cases permanent swarms--that survival of the fittest will establish these constant swarms where they are advantageous. But admitting this, we have also to admit a gradual rise of the associated state out of the solitary state. Wasps and bees present us with gradations. If, then, we are to understand how the organized societies have arisen, either out of the solitary state or out of undifferentiated swarms, we must assume that the differences of structure and instinct among the members of them arose little by little, as the social organization arose little by little. Fortunately we are able to trace the greater part of the process in the annually-formed communities of the common wasp; and we shall recognize in it an all-important factor (ignored by Professor Weismann) to which the phenomena, or at any rate the greater part of them, are due.

But before describing the wasp's annual history, let me set down certain observations made when, as a boy, I was given to angling, and, in July or August, sometimes used for bait "wasp-grubs," as they were called. After having had two or three days the combs or "cakes" of these, full of unfed larvæ in all stages of growth, I often saw some of them devouring the edges of their cells to satisfy their appetites; and saw others, probably the most advanced in growth, which were spinning the little covering caps to their cells, in preparation for assuming the pupa state. It is to be inferred that if, after a certain stage of growth has been reached, the food-supply becomes inadequate or is stopped altogether, the larva undergoes its transformation prematurely; and, as we shall presently see, this premature transformation has several natural sequences.

Let us return now to the wasp's family history. In the spring, a queen-wasp or mother-wasp which has survived the winter, begins to make a small nest containing four or more cells in which she lays eggs, and as fast as she builds additional cells, she lays an egg in each. Presently, to these activities, is added the feeding of the larvæ: one result being that the multiplication of larvæ involves a restriction of the food that can be given to each. If we suppose that the mother-wasp rears no more larvæ than she can fully feed, there will result queens or mothers like herself, relatively few in number. But if we suppose that, laying more numerous eggs she produces more larvæ than she can fully feed, the result will be that when these have reached a certain stage of growth, inadequate supply of food will be followed by premature retirement and transformation into pupæ. What will be the characters of the developed insects? The first effect of arrested nutrition will be smaller size. This we find. A second effect will be defective development of parts that are latest formed and least important for the survival of the individual. Hence we may look for arrested development of the reproductive organs--non-essential to individual life. And this expectation is in accord with what we see in animal development at large; for (passing over entirely sexless individuals) we see that though the reproductive organs may be marked out early in the course of development, they are not made fit for action until after the structures for carrying on individual life are nearly complete. The implication is, then, that an inadequately-fed and small larva will become a sterile imago. Having noted this, let us pass to a remarkable concomitant. In the course of development, organs are formed not alone in the order of their original succession, but partly in the order of importance and the share they have to take in adult activities--a change of order called by Haeckel "heterochrony." Hence the fact that we often see the maternal instinct precede the sexual instinct. Every little girl with her doll shows us that the one may become alive while the other remains dormant. In the case of wasps, then, premature arrest of development may result in incompleteness of the sexual traits, along with completeness of the maternal traits. What happens? Leave out the laying of eggs, and the energies of the mother-wasp are spent wholly in building cells and feeding larvæ, and the worker-wasp forthwith begins to spend its life in building cells and feeding larvæ. Thus interpreting the facts, we have no occasion to assume any constitutional difference between the eggs of worker-wasps and the eggs of queens; and that, their eggs are not different we see, first, in the fact that occasionally the worker-wasp is fertile and lays drone-producing eggs, and we see secondly that (if in this respect they are like the bees, of which, however, we have no proof) the larva of a worker-wasp can be changed into the larva of a queen-wasp by special feeding. But be this as it may, we have good evidence that the feeding determines everything. Says Dr. Ormerod, in his _British Social Wasps_:--

"When the swarm is strong and food plentiful ... the well fed larvæ develop into females, full, large, and overflowing with fat. There are all gradations of size, from the large fat female to the smallest worker.... The larger the wasp, the larger and better developed, as the rule, are the female organs, in all their details. In the largest wasps, which are to be the queens of another year, the ovaries differ to all appearances in nothing but their size from those of the larger worker wasps.... Small feeble swarms produce few or no perfect females; but in large strong swarms they are found by the score." (pp. 248-9)

To this evidence add the further evidence that queens and workers pass through certain parallel stages in respect of their maternal activities. At first the queen, besides laying eggs, builds cells and feeds larvæ, but after a time ceases to build cells, and feeds larvæ only, and eventually doing neither one nor the other, only lays eggs, and is supplied with food by the workers. So it is in part with the workers. While the members of each successive brood, when in full vigour, build cells and feed larvæ, by-and-by they cease to build cells, and only feed larvæ: the maternal activities and instincts undergo analogous changes. In this case, then, we are not obliged to assume that only by a process of natural selection can the differences of structure and instinct between queens and workers be produced. The only way in which natural selection here comes into play is in the better survival of the families of those queens which made as many cells, and laid as many eggs, as resulted in the best number of half-fed larvæ, producing workers; since by a rapid multiplication of workers the family is advantaged, and the ultimate production of more queens surviving into the next year insured.

The differentiation of classes does not go far among the wasps, because the cycle of processes is limited to a year, or rather to the few months of the summer. It goes further among the hive-bees, which, by storing food, survive from one year into the next. Unlike the queen-wasp, the queen-bee neither builds cells nor gathers food, but is fed by the workers: egg laying has become her sole business. On the other hand the workers, occupied exclusively in building and nursing, have the reproductive organs more dwarfed than they are in wasps. Still we see that the worker-bee occasionally lays drone-producing eggs, and that, by giving extra nutriment and the required extra space, a worker-larva can be developed into a queen-larva. In respect to the leading traits, therefore, the same interpretation holds. Doubtless there are subsidiary instincts which are apparently not thus interpretable. But before it can be assumed that an interpretation of another kind is necessary, it must be shown that these instincts cannot be traced back to those pre-social types and semi-social types which must have preceded the social types we now see. For unquestionably existing bees must have brought with them from the pre-social state an extensive endowment of instincts, and, acquiring other instincts during the unorganized social state, must have brought these into the present organized social state. It is clear, for instance, that the cell-building instinct in all its elaboration was mainly developed in the pre-social stage; for the transition from species building solitary cells to those building combs is traceable. We are similarly enabled to account for swarming as being an inheritance from remote ancestral types. For just in the same way that, with under-feeding of larvæ, there result individuals with imperfectly developed reproductive systems, so there will result individuals with imperfect sexual instincts; and just as the imperfect reproductive system partially operates upon occasion, so will the imperfect sexual instinct. Whence it will result that on the event which causes a queen to undertake a nuptial flight which is effectual, the workers may take abortive nuptial flights: so causing a swarm.

And here, before going further, let us note an instructive class of facts related to the class of facts above set forth. Summing up, in a chapter on "The Determination of Sex," an induction from many cases, Professor Geddes and Mr. Thompson remark that "such conditions as deficient or abnormal food," and others causing "preponderance of waste over repair ... tend to result in production of males;" while "abundant and rich nutrition" and other conditions which "favour constructive processes ... result in the production of females."[118] Among such evidences of this as immediately concern us, are these:--J. H. Fabre found that in the nests of _Osmia tricornis_, eggs at the bottom, first laid, and accompanied by much food, produced females, while those at the top, last laid, and accompanied by one-half or one-third the quantity of food, produced males,[119] Huber's observations on egg-laying by the honey-bee, show that in the normal course of things, the queen lays eggs of workers for eleven months, and only then lays eggs of drones: that is, when declining nutrition or exhaustion has set in. Further, we have the above-named fact, shown by wasps and bees, that when workers lay eggs these produce drones only.[120] Special evidence, harmonizing with general evidence, thus proves that among the social insects the sex is determined by degree of nutrition while the egg is being formed. See then how congruous this evidence is with the conclusion above drawn; for it is proved that after an egg, predetermined as a female, has been laid, the character of the produced insect as a perfect female or imperfect female is determined by the nutrition of the larva. _That is, one set of differences in structures and instincts is determined by nutrition before the egg is laid, and a further set of differences in structures and instincts is determined by nutrition after the egg is laid._

We come now to the extreme case--that of the ants. Is it not probable that the process of differentiation has been similar? There are sundry reasons for thinking so. With ants as with wasps and bees--the workers occasionally lay eggs; and an ant-community can, like a bee-community, when need be, produce queens out of worker-larvæ: presumably in the same manner by extra feeding. But here we have to add special evidence of great significance. For observe that the very facts concerning ants, which Professor Weismann names as exemplifying the formation of the worker type by selection, serve, as in the case of wasps, to exemplify its formation by arrested nutrition. He says that in several species the egg-tubes in the ovaries show progressive decrease in number; and this, like the different degrees of arrest in the ovaries of the worker-wasps, indicates arrest of larva-feeding at different stages. He gives cases showing that, in different degrees, the eyes of workers are less developed in the number of their facets than those of the perfect insects; and he also refers to the wings of workers as not being developed: remarking, however, that the rudiments of their wings show that the ancestral forms had wings. Are not these traits also results of arrested nutrition? Generally among insects the larvæ are either blind or have but rudimentary eyes; that is to say, visual organs are among the latest organs to arise in the genesis of the perfect organism. Hence early arrest of nutrition will stop formation of these, while various more ancient structures have become tolerably complete. Similarly with wings. Wings are late organs in insect phylogeny, and therefore will be among those most likely to abort where development is prematurely arrested. And both these traits will, for the same reason, naturally go along with arrested development of the reproductive system. Even more significant, however, is some evidence assigned by Mr. Darwin respecting the caste-gradations among the driver ants of West Africa. He says:--

"But the most important fact for us is, that, though the workers can be grouped into castes of different sizes, yet they graduate insensibly into each other, as does the widely-different structure of their jaws."[121]

"Graduate insensibly," he says; implying that there are very numerous intermediate forms. This is exactly what is to be expected if arrest of nutrition be the cause; for unless the ants have definite measures, enabling them to stop feeding at just the same stages, it must happen that the stoppage of feeding will be indefinite; and that, therefore, there will be all gradations between the extreme forms--"insensible gradations," both in size and in jaw-structure.

In contrast with this interpretation, consider now that of Professor Weismann. From whichever of the two possible suppositions he sets out, the result is equally fatal. If he is consistent, he must say that each of these intermediate forms of workers must have its special set of "determinants," causing its special set of modifications of organs; for he cannot assume that while perfect females and the extreme types of workers have their different sets of determinants, the intermediate types of workers have not. Hence we are introduced to the strange conclusion that besides the markedly-distinguished sets of determinants there must be, to produce these intermediate forms, many other sets slightly distinguished from one another--a score or more kinds of germ-plasm in addition to the four chief kinds. Next comes an introduction to the still stranger conclusion, that these numerous kinds of germ-plasm, producing these numerous intermediate forms, are not simply needless but injurious--produce forms not well fitted for either of the functions discharged by the extreme forms: the implication being that natural selection has originated these disadvantageous forms! If to escape from this necessity for suicide, Professor Weismann accepts the inference that the differences among these numerous intermediate forms are caused by arrested feeding of the larvæ at different stages, then he is bound to admit that the differences between the extreme forms, and between these and perfect females, are similarly caused. But if he does this, what becomes of his hypothesis that the several castes are constitutionally distinct, and result from the operation of natural selection? Observe, too, that his theory does not even allow him to make this choice; for we have clear proof that unlikenesses among the forms of the same species cannot be determined this way or that way by differences of nutrition. English greyhounds and Scotch greyhounds do not differ from one another so much as do the Amazon-workers from the inferior workers, or the workers from the queens. But no matter how a pregnant Scotch greyhound is fed, or her pups after they are born, they cannot be changed into English greyhounds: the different germ-plasms assert themselves spite of all treatment. But in these social insects the different structures of queens and workers _are_ determinable by differences of feeling. Therefore the production of their various castes does not result from the natural selection of varying germ-plasm.

Before dealing with Professor Weismann's crucial case--that co-adaptation of parts, which, in the soldier-ants, has, he thinks, arisen without inheritance of acquired characters--let me deal with an ancillary case which he puts forward as explicable by "panmixia alone." This is the "degeneration, in the warlike Amazon-ants, of the instinct to search for food."[122] Let us first ask what have been the probable antecedents of these Amazon-ants; for, as I have above said, it is absurd to speculate about the structures and instincts the species possesses in its existing organized social state without asking what structures and instincts it brought with it from its original solitary state and its unorganized social state. From the outset these ants were predatory. Some variety of them led to swarm--probably at the sexual season--did not again disperse so soon as other varieties. Those which thus kept together derived advantages from making simultaneous attacks on prey, and prospered accordingly. Of descendants the varieties which carried on longest the associated state prospered most; until, at length, the associated state became permanent. All which social progress took place while there existed only perfect males and females. What was the next step? Ants utilize other insects, and, among other ways of doing this, sometimes make their nests where there are useful insects ready to be utilized. Giving an account of certain New Zealand species of _Tetramorium_, Mr. W. W. Smith says they seek out underground places where there are "root-feeding aphides and coccids," which they begin to treat as domestic animals; and further he says that when, after the pairing season, new nests are being formed, there are "a few ants of both sexes ... from two up to eight or ten."[123] Carrying with us this fact as a key, let us ask what habits will be fallen into by the conquering species of ants. They, too, will seek places where there are creatures to be utilized; and, finding it profitable, will invade the habitations not of defenceless creatures only, but of creatures whose powers of defence are inadequate--weaker species of their own order. A very small modification will affiliate their habits on habits of their prototypes. Instead of being supplied with sweet substance excreted by the aphides they are supplied with sweet substance by the ants among which they parasitically settle themselves. How easily the subjugated ants may fall into the habit of feeding them, we shall see on remembering that already they feed not only larvæ but adults--individuals bigger than themselves. And that attentions kindred to these paid to parasitic ants may be established without difficulty, is shown us by the small birds which continue to feed a young cuckoo in their nest when it has outgrown them. This advanced form of parasitism grew up while there were yet only perfect males and females, as happens in the initial stage with these New Zealand ants. What further modifications of habits were probably then acquired? From the practice of settling themselves where there already exist colonies of aphides, which they carry about to suitable places in the nest, like _Tetramorium_, other ants pass to the practice of making excursions to get aphides, and putting them in better feeding places where they become more productive of saccharine matter. By a parallel step these soldier-ants pass from the stage of settling themselves among other ants which feed them, to the stage of fetching the pupæ of such ants to the nest: a transition like that which occurs among slave-making human beings. Thus by processes analogous to those we see going on, these communities of slave-making ants may be formed. And since the transition from an unorganized social state to a social state characterized by castes, must have been gradual, there must have been a long interval during which the perfect males and females of these conquering ants could acquire habits and transmit them to progeny. A small modification accounts for that seemingly-strange habit which Professor Weismann signalizes. For if, as is observed, those ants which keep aphides solicit them to excrete a supply of ant-food by stroking them with the antennæ, they come very near to doing that which Professor Weismann says the soldier-ants do towards a worker--"they come to it and beg for food:" the food being put into their mouths in this last case as almost or quite in the first. And evidently this habit of passively receiving food, continued through many generations of perfect males and females, may result in such disuse of the power of self-feeding that this is eventually lost. The behaviour of young birds, during, and after, their nest-life, gives us the clue. For a week or more after they are full-grown and fly about with their parents, they may be seen begging for food and making no efforts to recognize and pick up food for themselves. If, generation after generation, feeding of them in full measure continued, they would not learn to feed themselves: the perceptions and instincts implied in self-feeding would be later and later developed, until, with entire disuse of them, they would disappear altogether by inheritance. Thus self-feeding may readily have ceased among these soldier-ants before the caste-organization arose among them.

With this interpretation compare the interpretation of Professor Weismann. I have before protested against arguing in abstracts without descending to concretes. Here let us ask what are the particular changes which the alleged explanation by survival of the fittest involves. Suppose we make the very liberal supposition that an ant's central ganglion bears to its body the same ratio as the human brain bears to the human body--say, one-fortieth of its weight. Assuming this, what shall we assume to be the weight of those ganglion-cells and fibres in which are localized the perceptions of food and the suggestion to take it? Shall we say that these amount to one-tenth of the central ganglion? This is a high estimate considering all the impressions which this ganglion has to receive, and all the operations which it has to direct. Still we will say one-tenth. Then it follows that this portion of nervous substance is one-400th of the weight of its body. By what series of variations shall we say that it is reduced from full power to entire incapacity? Shall we say five? This is a small number to assume. Nevertheless we will assume it. What results? That the economy of nerve-substance achieved by each of these five variations will amount to one-2000th of the entire mass. Making these highly favourable assumptions, what follows:--The queen-ant lays eggs that give origin to individuals in each of which there is achieved an economy in nerve-substance of one-2000th of its weight; and the implication of the hypothesis is that such an economy will so advantage this ant-community that in the competition with other ant-communities it will conquer. For here let me recall the truth before insisted upon, that natural selection can operate only on those variations which appreciably benefit the stirp. Bearing in mind this requirement, is any one now prepared to say that survival of the fittest can cause this decline of the self-feeding faculty?[124]

Not limiting himself to the Darwinian interpretation, however, Professor Weismann says that this degradation may be accounted for by "panmixia alone." Here I will not discuss the adequacy of this supposed cause, but will leave it to be dealt with by implication a few pages in advance, where the general hypothesis of panmixia will be reconsidered.

And now, at length, we are prepared for dealing with Professor Weismann's crucial case--with his alleged disproof that co-adaptation of co-operative parts results from inheritance of acquired characters, because in the case of the Amazon-ants, it has arisen where the inheritance of acquired characters is impossible. For after what has been said, it will be manifest that the whole question is begged when it is assumed that this co-adaptation has arisen since there existed among these ants an organized social state. Unquestionably this organized social state pre-supposes a series of modifications through which it has been reached. It follows, then, that there can be no rational interpretation without a preceding inquiry concerning that earlier state in which there were no castes, but only males and females. What kinds of individuals were the ancestral ants--at first solitary, and then semi-social? They must have had marked powers of offence and defence. Of predacious creatures, it is the more powerful which form societies, not the weaker. Instance human races. Nations originate from the relatively warlike tribes, not from the relatively peaceful tribes. Among the several types of individuals forming the existing ant community, to which, then, did the ancestral ants bear the greatest resemblance? They could not have been like the queens, for these, now devoted to egg-laying, are unfitted for conquest. They could not have been like the inferior class of workers, for these, too, are inadequately armed and lack strength. Hence they must have been most like these Amazon-ants or soldier-ants, which now make predatory excursions--which now do, in fact, what their remote ancestors did. What follows? Their co-adapted parts have not been produced by the selection of variations within the ant-community, such as we now see it. They have been inherited from the pre-social and early social types of ants, in which the co-adaptation of parts had been effected by inheritance of acquired characters. It is not that the soldier-ants have gained these traits; it is that the other castes have lost them. Early arrest of development causes absence of them in the inferior workers; and from the queens they have slowly disappeared by inheritance of the effects of disuse. For, in conformity with ordinary facts of development, we may conclude that in a larva which is being so fed as that the development of the reproductive organs is becoming pronounced, there will simultaneously commence arrest in the development of those organs which are not to be used. There are abundant proofs that along with rapid growth of some organs others abort. And if these inferences are true, then Professor Weismann's argument falls to the ground. Nay, it falls to the ground even if conclusions so definite as these be not insisted upon; for before he can get a basis for his argument he must give good reasons for concluding that these traits of the Amazon-ants have _not_ been inherited from remote ancestors.

One more step remains. Let us grant him his basis, and let us pass from the above negative criticism to a positive criticism. As before, I decline to follow the practice of talking in abstracts instead of in concretes, and contend that, difficult as it may be to see how natural selection has in all cases operated, we ought, at any rate, to trace out its operation whenever we can, and see where the hypothesis lands us. According to Professor Weismann's admission, for production of the Amazon-ant by natural selection, "_many parts must have varied simultaneously and in harmony with one another_;"[125] and he names as such, larger jaws, muscles to move them, larger head, and thicker chitin for it, bigger nerves for the muscles, bigger motor centres in the brain, and, for the support of the big head, strengthening of the thorax, limbs, and skeleton generally. As he admits, all these parts must have varied simultaneously in due proportion to one another. What must have been the proximate causes of their variations? They must have been variations in what he calls the "determinants." He says:--

"We have, however, to deal with the transmission of parts which are _variable_ and this necessitates the assumption that just as many independent and variable parts exist in the germ-plasm as are present in the fully formed organism."[126]

Consequently to produce simultaneously these many variations of parts, adjusted in their sizes and shapes, there must have simultaneously arisen a set of corresponding variations in the "determinants" composing the germ-plasm. What made them simultaneously vary in the requisite ways? Professor Weismann will not say that there was somewhere a foregone intention. This would imply supernatural agency. He makes no attempt to assign a physical cause for these simultaneous appropriate variations in the determinants: an adequate physical cause being inconceivable. What, then, remains as the only possible interpretation? Nothing but _a fortuitous concourse of variations_; reminding us of the old "fortuitous concourse of atoms." Nay, indeed, it is the very same thing. For each of the "determinants," made up of "biophors," and these again of protein-molecules, and these again of simpler chemical molecules, must have had its molecular constitution changed in the required way; and the molecular constitutions of all the "determinants," severally modified differently, but in adjustment to one another, must have been thus modified by "a fortuitous concourse of atoms." Now if this is an allowable supposition in respect of the "determinants," and the varying organs arising from them, why is it not an allowable supposition in respect of the organism as a whole? Why not assume "a fortuitous concourse of atoms" in its broad, simple form? Nay, indeed, would not this be much the easier? For observe, this co-adaptation of numerous co-operative parts is not achieved by one set of variations, but is achieved gradually by a series of such sets. That is to say, the "fortuitous concourse of atoms" must have occurred time after time in appropriate ways. We have not one miracle, but a series of miracles!

* * * * *

Of the two remaining points in Professor Weismann's first article which demand notice, one concerns his reply to my argument drawn from the distribution of tactual discriminativeness. In what way does he treat this argument? He meets it by an argument derived from hypothetical evidence--not actual evidence. Taking the case of the tongue-tip, I have carefully inquired whether its extreme power of tactual discrimination can give any life-saving advantage in moving about the food during mastication, in detecting foreign bodies in it, or for purposes of speech; and have, I think, shown that the ability to distinguish between points one twenty-fourth of an inch apart is useless for such purposes. Professor Weismann thinks he disposes of this by observing that among the apes the tongue is used as an organ of touch. But surely a counter-argument equivalent in weight to mine should have given a case in which power to discriminate between points one twenty-fourth of an inch apart instead of one-twentieth of an inch apart (a variation of one-sixth) had a life-saving efficacy; or, at any rate, should have suggested such a case. Nothing of the kind is done or even attempted. But now note that his reply, accepted even as it stands, is suicidal. For what has the trusted process of panmixia been doing ever since the human being began to evolve from the ape? Why during thousands of generations has not the nervous structure giving this extreme discriminativeness dwindled away? Even supposing it had been proved of life-saving efficacy to our simian ancestors, it ought, according to Professor Weismann's own hypothesis, to have disappeared in us. Either there was none of the assumed special capacity in the ape's tongue, in which case his reply fails, or panmixia has not operated, in which case his theory of degeneracy fails.

All this, however, is but preface to the chief answer. The argument drawn from the case of the tongue-tip, with which alone Professor Weismann deals, is but a small part of my argument, the remainder of which he does not attempt to touch--does not even mention. Had I never referred to the tongue-tip at all, the various contrasts in discriminativeness which I have named, between the one extreme of the forefinger-tip and the other extreme of the middle of the back, would have abundantly sufficed to establish my case--would have sufficed to show the inadequacy of natural selection as a key and the adequacy of the inheritance of acquired characters.

It seems to me, then, that judgment must go against him by default. Practically he leaves the matter standing just where it did.[127]

The other remaining point concerns the vexed question of panmixia. Confirming the statement of Dr. Romanes, Professor Weismann says that I have misunderstood him. Already (_Contemporary Review_, May, 1893, p. 758, and Reprint, p. 66) I have quoted passages which appeared to justify my interpretation, arrived at after much seeking.[128] Already, too, in this review (July, 1893, p. 54) I have said why I did not hit upon the interpretation now said to be the true one: I never supposed that any one would assume, without assigned cause, that (apart from the excluded influence of disuse) the _minus_ variations of a disused organ are greater than the _plus_ variations. This was a tacit challenge to produce reasons for the assumption. Professor Weismann does not accept the challenge, but simply says:--"In my opinion all organs are maintained at the height of their development only through uninterrupted selection" (p. 332): in the absence of which they decline. Now it is doubtless true that as a naturalist he may claim for his "opinion" a relatively great weight. Still, in pursuance of the methods of science, it seems to me that something more than an opinion is required as the basis of a far-reaching theory.[129]

Though the counter-opinion of one who is not a naturalist (as Professor Weismann points out) may be of relatively small value, yet I must here again give it, along with a final reason for it. And this reason shall be exhibited, not in a qualitative form, but in a quantitative form. Let us quantify the terms of the hypothesis by weights; and let us take as our test case the rudimentary hind-limbs of the whale. Zoologists are agreed that the whale has been evolved from a mammal which took to aquatic habits, and that its disused hind-limbs have gradually disappeared. When they ceased to be used in swimming, natural selection played a part--probably an important part--in decreasing them; since, being then impediments to movement through the water, they diminished the attainable speed. It may be, too, that for a period after disappearance of the limbs beneath the skin, survival of the fittest had still some effect. But during the latter stages of the process it had no effect; since the rudiments caused no inconvenience and entailed no appreciable cost. Here, therefore, the cause, if Professor Weismann is right, must have been panmixia. Dr. Struthers, Professor of Anatomy at Aberdeen, whose various publications show him to be a high, if not the highest, authority on the anatomy of these great cetaceans, has kindly taken much trouble in furnishing me with the needful data, based upon direct weighing and measuring and estimation of specific gravity. In the Black Whale (_Balænoptera borealis_) there are no rudiments of hind-limbs whatever: rudiments of the pelvic bones only remain. A sample of the Greenland Right Whale, estimated to weigh 44,800 lbs., had femurs weighing together 3½ ozs.; while a sample of the Razor-back Whale (_Balænoptera musculus_), 50 feet long, and estimated to weigh 56,000 lbs., had rudimentary femurs weighing together one ounce; so that these vanishing remnants of hind-limbs weighed but one-896,000th part of the animal. Now in considering the alleged degeneration by panmixia, we have first to ask why these femurs must be supposed to have varied in the direction of decrease rather than in the direction of increase. During its evolution from the original land-mammal, the whale has grown enormously, implying habitual excess of nutrition. Alike in the embryo and in the growing animal, there must have been a chronic plethora. Why, then, should we suppose these rudiments to have become smaller? Why should they not have enlarged by deposit in them of superfluous materials? But let us grant the unwarranted assumption of predominant _minus_ variations. Let us say that the last variation was a reduction of one-half--that in some individuals the joint weight of the femurs was suddenly reduced from two ounces to one ounce--a reduction of one-900,000th of the creature's weight. By inter-crossing with those inheriting the variation, the reduction, or a part of the reduction, was made a trait of the species. Now, in the first place, a necessary implication is that this _minus_ variation was maintained in posterity. So far from having reason to suppose this, we have reason to suppose the contrary. As before quoted, Mr. Darwin says that "unless carefully preserved by man," "any particular variation would generally be lost by crossing, reversion, and the accidental destruction of the varying individuals."[130] And Mr. Galton, in his essay on "Regression towards Mediocrity,"[131] contends that not only do deviations of the whole organism from the mean size tend to thus disappear, but that deviations in its components do so. Hence the chances are against such _minus_ variation being so preserved as to affect the species by panmixia. In the second place, supposing it to be preserved, may we reasonably assume that, by inter-crossing, this decrease, amounting to about a millionth part of the creature's weight, will gradually affect the constitutions of all Razor-back Whales distributed over the Arctic seas and the North Atlantic Ocean, from Greenland to the Equator? Is this a credible conclusion? For three reasons, then, the hypothesis must be rejected.

Thus, the only reasonable interpretation is the inheritance of acquired characters. If the effects of use and disuse, which are known causes of change in each individual, influence succeeding individuals--if functionally-produced modifications of structure are transmissible, as well as modifications of structure otherwise arising--then this reduction of the whale's hind limbs to minute rudiments is accounted for. The cause has been unceasingly operative on all individuals of the species ever since the transformation began.

In one case see all. If this cause has thus operated on the limbs of the whale, it has thus operated in all creatures on all parts having active functions.

* * * * *

At the outset I intimated that I must limit my replies to those arguments of Professor Weismann which are contained in his first article. That those contained in his second might be dealt with no less effectually, did time and space permit, is manifest to me; but about the probability of this the reader must form his own judgment. My replies thus far may be summed up as follows:--

Professor Weismann says he has disproved the conclusion that degeneration of the little toe has resulted from inheritance of acquired characters. But his reasoning fails against an interpretation he overlooks. A profound modification of the hind limbs and their appendages must have taken place during the transition from arboreal habits to terrestrial habits; and dwindling of the little toe is an obvious consequence of disuse, at the same time that enlargement of the great toe is an obvious consequence of increased use.

The entire argument based on the unlike forms and instincts presented by castes of social insects is invalidated by an omission. Until probable conclusions are reached respecting the characters which such insects brought with them into the organized social state, no valid inferences can be drawn respecting characters developed during that state.

A further large error of interpretation is involved in the assumption that the different caste-characters are transmitted to them in the eggs laid by the mother insect. While we have evidence that the unlike structures of the sexes are determined by nutrition of the germ before egg-laying, we have evidence that the unlike structures of classes are caused by unlikenesses of nutrition of the larvæ. That these varieties of forms do not result from varieties of germ-plasms, is demonstrated by the fact that where there are varieties of germ-plasms, as in varieties of the same species of mammal, no deviations in feeding prevent display of their structural results.

For such caste-modifications as those of the Amazon-ants, which are unable to feed themselves, there is a feasible explanation other than Professor Weismann's. The relation of common ants to their domestic animals--aphides and coccids--which yield them food on solicitation, does not differ widely from this relation between these Amazon-ants and their domestic animals--the slave-ants. And the habit of being fed, contracted during the first stages of their parasitic life, when there were perfect males and females, may, during that stage, have become established by inheritance. Meanwhile the opposed interpretation--that this incapacity has resulted from the selection of those ant-communities the queens of which laid eggs that had so varied as to entail this incapacity--implies that a scarcely appreciable economy of nerve-matter advantaged the stirp so greatly as to cause it to spread more than other stirps: an incredible supposition.

As the outcome of these alternative interpretations we saw that the argument respecting the co-adaptation of co-operative parts, which Professor Weismann thinks is furnished to him by the Amazon-ants, disappears. The ancestral ants were conquering ants. These founded the communities; and hence those members of the present communities which are most like them are the Amazon-ants. If so, the co-adaptation of the co-operative parts was effected by inheritance during the solitary and semi-social stages. Even were there no such solution, the opposed solution will be unacceptable. These simultaneous appropriate variations of the co-operative parts in sizes, shapes, and proportions, are supposed to be effected by simultaneous variations in the "determinants" of the germ-plasms; and in the absence of an assigned physical cause, this implies a fortuitous concourse of appropriate variations, which carries us back to a "fortuitous concourse of atoms." This may just as well be extended to the entire organism. The old hypothesis of special creations is more consistent and comprehensible.

To rebut my inference drawn from the distribution of discriminativeness, Professor Weismann uses not an argument but the blank form of an argument. The ability to discriminate one twenty-fourth of an inch by the tongue-tip _may_ have been useful to the ape: no conceivable use being even suggested. And then the great body of my argument derived from the distribution of discriminativeness over the skin, which amply suffices, is wholly ignored.

The tacit challenge I gave to name some facts in support of the hypothesis of panmixia--or even a solitary fact--is passed by. It remains a pure speculation having no basis but Professor Weismann's "opinion." When from the abstract statement of it we pass to a concrete test, in the case of the whale, we find that it necessitates an unproved and improbable assumption respecting _plus_ and _minus_ variations; that it ignores the unceasing tendency to reversion; and that it implies an effect out of all proportion to the cause.

It is curious what entirely opposite conclusions men may draw from the same evidence. Professor Weismann thinks he has shown that the "last bulwark of the Lamarckian principle is untenable." Most readers will hold with me that he is, to use the mildest word, premature in so thinking. Contrariwise my impression is that he has not shown either this bulwark or any other bulwark to be untenable; but rather that while his assault has failed it has furnished opportunity for strengthening sundry of the bulwarks.

IV.

Among those who follow a controversy to its close, not one in a hundred turns back to its beginning to see whether its chief theses have been dealt with. Very often the leading arguments of one disputant, seen by the other to be unanswerable, are quietly ignored, and attention is concentrated on subordinate arguments to which replies, actually or seemingly valid, can be made. The original issue is thus commonly lost sight of.

More than once I have pointed out that, as influencing men's views about Education, Ethics, Sociology, and Politics, the question whether acquired characters are inherited is the most important question before the scientific world. Hence I cannot allow the discussion with Professor Weismann to end in so futile a way as it will do if no summary of results is made. Here, therefore, I propose to recapitulate the whole case in brief. Primarily my purpose is to recall certain leading propositions which, having been passed by unnoticed, remain outstanding. I will turn, in the second place, to such propositions as have been dealt with; hoping to show that the replies given are invalid, and consequently that these propositions also remain outstanding.

But something beyond a summing-up is intended. A few pages at the close will be devoted to setting forth new evidence which has come to light since the controversy commenced--evidence which many will think sufficient in itself to warrant a positive conclusion.

* * * * *

The fact that the tip of the fore finger has thirty times the power of discrimination possessed by the middle of the back, and that various intermediate degrees of discriminative power are possessed by various parts of the skin, was set down as a datum for my first argument. The causes which might be assigned for these remarkable contrasts were carefully examined under all their aspects. I showed in detail that the contrasts could not in any way be accounted for by natural selection. I further showed that no interpretation of them is afforded by the alleged process of panmixia: this has no _locus standi_ in the case. Having proved experimentally, that ability of the fingers to discriminate is increased by practice, and having pointed out that gradations of discriminativeness in different parts correspond with gradations in the activities of the parts as used for tactual exploration, I argued that these contrasts have arisen from the organized and inherited effects of tactual converse with surrounding things, varying in its degrees according to the positions of the parts--in other words, that they are due to the inheritance of acquired characters. As a crowning proof I instanced the case of the tongue-tip, which has twice the discriminativeness of the forefinger-tip: pointing out that consciously, or semi-consciously, or unconsciously, the tongue-tip is perpetually exploring the inner surfaces of the teeth.

Singling out this last case, Professor Weismann made, or rather adopted from Dr. Romanes, what professed to be a reply but was nothing more than the blank form of a reply. It was said that though this extreme discriminativeness of the tongue-tip is of no use to mankind, it may have been of use to certain ancestral _primates_. No evidence of any such use was given; no imaginable use was assigned. It was simply suggested that there perhaps was a use.

In my rejoinder, after indicating the illusory nature of this proceeding (which is much like offering a cheque on a bank where no assets have been deposited to meet it), I pointed out that had the evidence furnished by the tongue tip never been mentioned, the evidence otherwise furnished amply sufficed. I then drew attention to the fact that this evidence had been passed over, and tacitly inquired why.

No reply.[132]

* * * * *

In his essay on "The All-Sufficiency of Natural Selection," Professor Weismann set out, not by answering one of the arguments I had used, but by importing into the discussion an argument used by another writer, which it was easy to meet. It had been contended that the smallness and deformity of the little toe are consequent upon the effects of boot-pressure, inherited from generation to generation. To this Professor Weismann made the sufficient reply that the fusion of the phalanges and otherwise degraded structure of the little toe, exist among peoples who go barefoot.

In my "Rejoinder" I said that though the inheritance of acquired characters does not explain this degradation in the way alleged, it explains it in a way which Professor Weismann overlooks. The cause is one which has been operating ever since the earliest anthropoid creatures began to decrease their life in trees and increase their life on the earth's surface. The mechanics of walking and running, in so far as they concern the question at issue, were analyzed; and it was shown that effort is economized and efficiency increased in proportion as the stress is thrown more and more on the inner digits of the foot and less and less on the outer digits. So that thus the foot furnishes us simultaneously with an instance of increase from use and of decrease from disuse; a further disproof being yielded of the allegation that co-operative parts vary together, since we have here co-operative parts of which one grows while the other dwindles.

I ended by pointing out that, so far from strengthening his own case, Professor Weismann had, by bringing into the controversy this changed structure of the foot, given occasion for strengthening the opposite case.

No reply.

* * * * *

We come now to Professor Weismann's endeavour to disprove my second thesis--that it is impossible to explain by natural selection alone the co-adaptation of co-operative parts. It is thirty years since this was set forth in _The Principles of Biology_. In § 166 I instanced the enormous horns of the extinct Irish elk, and contended that in this, and in kindred cases, where for the efficient use of some one enlarged part many other parts have to be simultaneously enlarged, it is out of the question to suppose that they can have all spontaneously varied in the required proportions. In "The Factors of Organic Evolution," by way of enforcing this argument, which had, so far as I know, never been met, I dwelt upon the aberrant structure of the giraffe. And then, in the essay which initiated this controversy, I brought forward yet a third case--that of an animal which, previously accustomed only to walking, acquires the power of leaping.

In the first of his articles in the _Contemporary Review_ (September, 1893), Professor Weismann made no direct reply, but he made an indirect reply. He did not attempt to show how there could have taken place in the stag the "harmonious variation of the different parts that co-operate to produce one physiological result" (p. 311); but he contended that such harmonious variation _must_ have taken place, because the like has taken place in "the neuters of state-forming insects"--"animal forms which do not reproduce themselves, but are always propagated anew by parents which are unlike them" (p. 313), and which therefore cannot have transmitted acquired characters. Singling out those soldier-neuters which exist among certain kinds of ants, he described (p. 318) the many co-ordinated parts required to make their fighting organs efficient. He then argued that the required simultaneous changes can "only have arisen by a selection of the parent-ants dependent on the fact that those parents which produced the best workers had always the best prospect of the persistence of their colony. No other explanation is conceivable; _and it is just because no other explanation is conceivable, that it is necessary for us to accept the principle of natural selection_" (pp. 318-9).

[This passage initiated a collateral controversy, which, as continually happens, has greatly obscured the primary controversy. It became a question whether these forms of neuter insects have arisen as Professor Weismann assumes, or whether they have arisen from arrested development consequent upon innutrition. To avoid entanglements I must for the present pass over this collateral controversy, intending to resume it presently, when the original issues have been dealt with.]

No one will suspect me of thinking that the inconceivability of the negation is not a valid criterion, since, in "The Universal Postulate," published in the _Westminster Review_ in 1852 and afterwards in _The Principles of Psychology_, I contended that it is the ultimate test of truth. But then in every case there has to be determined the question--Is the negation inconceivable; and in assuming that it is so in the case named, lies the fallacy of the above-quoted passage. The three separate ways in which I dealt with this position of Professor Weismann are as follows:--

If we admit the assumption that the form of the soldier-ant has been developed since the establishment of the organized ant-community in which it exists, Professor Weismann's assertion that no other process than that which he alleges is conceivable, is true. But I pointed out that this assumption is inadmissible; and that no valid conclusion respecting the genesis of the soldier-ant can be drawn without postulating either the ascertained, or the probable, structure of those pre-social, or semi-social, ants from which the organized social ants have descended. I went on to contend that the pre-social type must have been a conquering type, and that therefore in all probability the soldier-ants represent most nearly the structures of those ancestral ants which existed when the society had perfect males and females and could transmit acquired characters, while the other members of the existing communities are degraded forms of the type.

No reply.

A further argument I used was that where there exist different castes among the neuter-ants, as those seen in the soldiers and workers of the Driver ants of West Africa, "they graduate insensibly into each other" alike in their sizes and in their structures; and that Professor Weismann's hypothesis implies a special set of "determinants" for each intermediate form. Or if he should say that the intermediate forms result from mixtures of the determinants of the two extreme forms, there still remains the further difficulty that natural selection has maintained, for innumerable generations, these intermediate forms which are injurious deviations from the useful extreme forms.

No reply.

One further reason--fatal it seems to me--was urged in bar of his interpretation. No physical cause has been, or can be, assigned, why in the germ-plasm of any particular queen-ant, the "determinants" initiating these various co-operative organs, all simultaneously vary in fitting ways and degrees, and still less why there occur such co-ordinated variations generation after generation, until by their accumulated results these efficient co-operative structures have been evolved. I pointed out that in the absence of any assigned or assignable physical cause, it is necessary to assume a fortuitous concurrence of favourable variations, which means "a fortuitous concourse of atoms;" and that it would be just as rational, and much more consistent, to assume that the structure of the entire organism thus resulted.

No reply.

* * * * *

It is reasonable to suspect that Professor Weismann recognized these difficulties as insuperable, for, in his Romanes Lecture on "The Effect of External Influences upon Development," instead of his previous indirect reply, he makes a direct reply. Reverting to the stag and its enlarging horns, he alleges a process by which, as he thinks, we may understand how, by variation and selection, all the bones and muscles of the neck, of the thorax, and of the fore-legs, are step by step adjusted in their sizes to the increasing sizes of the horns. He ascribes this harmonization to the internal struggle for nutriment, and that survival of the fittest which takes place among the parts of an organism: a process which he calls "_intra-individual_-selection, or more briefly--_intra-selection_" (p. 12).

"Wilhelm Roux has given an explanation of the cause of these wonderfully fine adaptations by applying the principle of selection to the parts of the organism. Just as there is a struggle for survival among the individuals of a species, and the fittest are victorious, so also do even the smallest living particles contend with one another, and those that succeed best in securing food and place grow and multiply rapidly, and so displace those that are less suitably equipped" (p. 12).[133]

That I do not explain as he does the co-adaptation of co-operative parts, Professor Weismann ascribes to my having overlooked this "principle of intra-selection"--an unlucky supposition, as we see. But I do not think that when recognizing it a generation ago, I should have seen its relevancy to the question at issue, had that issue then been raised, and I certainly do not see it now. Full reproduction of Professor Weismann's explanation is impracticable, for it occupies several pages, but here are the essential sentences from it:--

"The great significance of intra-selection appears to me not to depend on its producing structures that are directly transmissible,--it cannot do that,--but rather consists in its causing a development of the germ-structure, acquired by the selection of individuals, which will be suitable to varying conditions.... We may therefore say that intra-selection effects the adaptation of the individual to its chance developmental conditions,--the suiting of the hereditary primary constituents to fresh circumstances" (p. 16).... "But as the primary variations in the phyletic metamorphosis occurred little by little, the secondary adaptations would probably as a rule be able to keep pace with them. Time would thus be gained till, in the course of generations, by constant selection of those germs the primary constituents of which are best suited to one another, the greatest possible degree of harmony may be reached, and consequently a definitive metamorphosis of the species involving all the parts of the individual may occur" (p. 19).

The connecting sentences, along with those which precede and succeed, would not, if quoted, give to the reader clearer conceptions than these by themselves give. But when disentangled from Professor Weismann's involved statements, the essential issues are, I think, clear enough. In the case of the stag, that daily working together of the numerous nerves, muscles, and bones concerned, by which they are adjusted to the carrying and using of somewhat heavier horns, produces on them effects which, as I hold, are inheritable, but which, as Professor Weismann holds, are not inheritable. If they are not inheritable, what must happen? A fawn of the next generation is born with no such adjustment of nerves, muscles and bones as had been produced by greater exercise in the parent, and with no tendency to such adjustment. Consequently if, in successive generations, the horns go on enlarging, all these nerves, muscles, and bones, remaining of the original sizes, become utterly inadequate. The result is loss of life: the process of adaptation fails. "No," says Professor Weismann, "we must conclude that the germ-plasm has varied in the needful manner." How so? The process of "intra-individual selection," as he calls it, can have had no effect, since the cells of the soma cannot influence the reproductive cells. In what way, then, has the germ-plasm gained the characters required for producing simultaneously all these modified co-operative parts. Well, Professor Weismann tells us merely that we must suppose that the germ-plasm acquires a certain sensitiveness such as gives it a proclivity to development in the requisite ways. How is such proclivity obtainable? Only by having a multitude of its "determinants" simultaneously changed in fit modes. Emphasizing the fact that even a small failure in any one of the co-operative parts may be fatal, as the sprain of an over-taxed muscle shows us, I alleged that the chances are infinity to one against the needful variations taking place at the same time. Divested of its elaboration, its abstract words and technical phrases, the outcome of Professor Weismann's explanation is that he accepts this, and asserts that the infinitely improbable thing takes place!

Either his argument is a disguised admission of the inheritableness of acquired characters (the effects of "intra-selection") or else it is, as before, the assumption of a fortuitous concourse of favourable variations in the determinants--"a fortuitous concourse of atoms."

* * * * *

Leaving here this main issue, I return now to that collateral issue named on a preceding page as being postponed--whether the neuters among social insects result from specially modified germ-plasms or whether they result from the treatment received during their larval stages.

For the substantiation of his doctrine Professor Weismann is obliged to adopt the first of these alternatives; and in his Romanes Lecture he found it needful to deal with the evidence I brought in support of the second alternative. He says that "poor feeding is not the _causa efficiens_ of sterility among bees, but is merely the stimulus which _not only results in the formation of rudimentary ovaries, but at the same time calls forth all the other distinctive characters of the workers_" (pp. 29-30); and he says this although he has in preceding lines admitted that it is "true of all animals that they reproduce only feebly or not at all when badly and insufficiently nourished:" a known cause being thus displaced by a supposed cause. But Professor Weismann proceeds to justify his interpretation by experimentally-obtained evidence.

He "reared large numbers of the eggs of a female blow-fly"; the larvæ of some he fed abundantly, but the larvæ of others sparingly; and eventually he obtained, from the one set flies of full size, and from the other small flies. Nevertheless the small flies were fertile, as well as the others. Here, then, was proof that innutrition had not produced infertility; and he contends that therefore among the neuter social insects, infertility has not resulted from innutrition. The argument seems strong, and to many will appear conclusive; but there are two differences which entirely vitiate the comparison Professor Weismann institutes.

One of them has been pointed out by Mr. Cunningham. In the case of the blow-fly the food supplied to the larvæ though different in quantity was the same in quality; in the case of the social insects the food supplied, whether or not different in quantity, differs in quality. Among bees, wasps, ants, &c., the larvæ of the reproductive forms are fed upon a more nitrogenous food than are the larvæ of the workers; whereas the two sets of larvæ of the blow-fly, as fed by Professor Weismann, were alike supplied with highly nitrogenous food. Hence there did not exist the same cause for non-development of the reproductive organs. Here, then, is one vitiation of the supposed parallel. There is a second.

While the development of an embryo follows in a rude way the phyletic metamorphoses passed through by its ancestry, the order of development of organs is often gradually modified by the needs of particular species: the structures being developed in such order as conduces to self-sustentation and the welfare of offspring. Among other results there arise differences in the relative dates of maturity of the reproductive system and of the other systems. It is clear, _à priori_, that it must be fatal to a species if offspring are habitually produced before the conditions requisite for their survival are fulfilled. And hence, if the life is a complex one, and the care taken of offspring is great, reproduction must be much longer delayed than where the life is simple and the care of offspring absent or easy. The contrast between men and oxen sufficiently illustrates this truth. Now the subordination of the order of development of parts to the needs of the species, is conspicuously shown in the contrast between these two kinds of insects which Professor Weismann compares as though their requirements were similar. What happens with the blow fly? If it is able to suck up some nutriment, to fly tolerably, and to scent out dead flesh, various of its minor organs may be more or less imperfect without appreciable detriment to the species: the eggs can be laid in a fit place, and that is all that is wanted. Hence it profits the species to have the reproductive system developed comparatively early--in advance, even, of various less essential parts. Quite otherwise is it with social insects, which take such remarkable care of their young; or rather to make the case parallel--quite otherwise is it with those types from which the social insects have descended, bringing into the social state their inherited instincts and constitutions. Consider the doings of the mason-wasp, or mason-bee, or those of the carpenter-bee. What, in these cases, must the female do that she may rear members of the next generation? There is a fit place for building or burrowing to be chosen; there is the collecting together of grains of sand and cementing them into a strong and water-proof cell, or there is the burrowing into wood and there building several cells; there is the collecting of food to place along with the eggs deposited in these cells, solitary or associated, including that intelligent choice of small caterpillars which, discovered and carried home, are carefully packed away and hypnotized by a sting, so that they may live until the growing larva has need of them. For all these proceedings there have to be provided the fit external organs--cutting instruments, &c., and the fit internal organs--complicated nerve-centres in which are located these various remarkable instincts, and ganglia by which these delicate operations have to be guided. And these special structures have, some if not all of them, to be made perfect and brought into efficient action before egg-laying takes place. Ask what would happen if the reproductive system were active in advance of these ancillary appliances. The eggs would have to be laid without protection or food, and the species would forthwith disappear. And if that full development of the reproductive organs which is marked by their activity, is not needful until these ancillary organs have come into play, the implication, in conformity with the general law above indicated, is that the perfect development of the reproductive organs will take place later than that of these ancillary organs, and that if innutrition checks the general development, the reproductive organs will be those which chiefly suffer. Hence, in the social types which have descended from these solitary types, this order of evolution of parts will be inherited, and will entail the results I have inferred.

If only deductively reached, this conclusion would, I think, be fully justified. But now observe that it is more than deductively reached. It is established by observation. Professor Riley, Ph.D., late Government Entomologist of the United States, in his annual address as President of the Biological Society of Washington,[134] on January 29, 1894, said:--

"Among the more curious facts connected with these Termites, because of their exceptional nature, is the late development of the internal sexual organs in the reproductive forms." (p. 34.)

Though what has been shown of the Termites has not been shown of the other social insects, which belong to a different order, yet, considering the analogies between their social states and between their constitutional requirements, it is a fair inference that what holds in the one case holds partially, if not fully, in the other. Should it be said that the larval forms do not pass into the pupa state in the one case as they do in the other, the answer is that this does not affect the principle. The larva carries into the pupa state a fixed quantity of tissue-forming material for the production of the imago. If the material is sufficient, then a complete imago is formed. If it is not sufficient, then, while the earlier formed organs are not affected by the deficiency, the deficiency is felt when the latest formed organs come to be developed, and they are consequently imperfect.

Even if left without reply, Professor Weismann's interpretation commits him to some insuperable difficulties, which I must now point out. Unquestionably he has "the courage of his opinions;" and it is shown throughout this collateral discussion as elsewhere. He is compelled by accumulated evidence to admit "that there is only _one_ kind of egg from which queens and workers as well as males arise."[135] But if the production of one or other form from the same germ does not result from speciality of feeding, what does it result from? Here is his reply:--

"We must rather suppose that the primary constituents of two distinct reproductive systems--_e. g._ those of the queen and worker--are contained in the germ-plasm of the egg."[136]

"The courage of his opinions," which Professor Weismann shows in this assumption, is, however, quite insufficient. For since he himself has just admitted that there is only one kind of egg for queens, workers, and males, he must at any rate assume three sets of "determinants." (I find that on a subsequent page he does so.) But this is not enough, for there are, in many cases, two if not more kinds of workers, which implies that four sets of determinants must co-exist in the same egg. Even now we have not got to the extent of the assumption required. In the address above referred to on "Social Insects from Psychical and Evolutional Points of View," Professor Riley gives us (p. 33) the--

_Forms in a Termes Colony under Normal Conditions._

1. Youngest larvæ. / \ / \ / \ 2. Larvæ [of those] unfit 3. Larvæ [that will be] fit for reproduction. for reproduction. / \ / \ / \ / \ 4. Larvæ of 5. Larvæ of 8. Nymphs of 9. Nymphs of 2nd workers. soldiers. 1st form. form. | | | 6. Workers. 7. Soldiers. 10. Winged forms. | 11. True royal pairs.

Hence as, in this family tree, the royal pair includes male and female, it results that there are _five_ different adult forms (Grassi says there are two others) arising from like eggs or larvæ; and Professor Weismann's hypothesis becomes proportionately complicated. Let us observe what the complications are.

It often happens in controversy--metaphysical controversy more than any other--that propositions are accepted without their terms having been mentally represented. In public proceedings documents are often "taken as read," sometimes with mischievous results; and in discussions propositions are often taken as thought when they have not been thought and cannot be thought. It sufficiently taxes imagination to assume, as Professor Weismann does, that two sets of "ids" or of "determinants" in the same egg are, throughout all the cell-divisions which end in the formation of the _morula_, kept separate, so that they may subsequently energize independently; or that if they are not thus kept separate, they have the power of segregating in the required ways. But what are we to say when three, four, and even five sets of "ids" or bundles of "determinants" are present? How is dichotomous division to keep these sets distinct; or if they are not kept distinct, what shall we say to the chaos which must arise after many fissions, when each set in conflict with the others strives to produce its particular structure? And how are the conquering determinants to find they ways out of the _mêlée_ to the places where they are to fulfil their organizing functions? Even were they all intelligent beings and each had a map by which to guide his movements, the problem would be sufficiently puzzling. Can we assume it to be solved by unconscious units?

Thus even had Professor Weismann shown that the special structures of the different individuals in an insect-community are not due to differences in the nurtures they receive, which he has failed to do, he would still be met by this difficulty in the way of his own view, in addition to the three other insuperable difficulties grouped together in a preceding section.

* * * * *

The collateral issue, which has occupied the largest space in the controversy, has, as commonly happens, begotten a second generation of collateral issues. Some of these are embodied in the form of questions put to me, which I must here answer, lest it should be supposed that they are unanswerable and my view therefore untenable.

In the notes he appends to his Romanes Lecture, Professor Weismann writes:--

"One of the questions put to Spencer by Ball is quite sufficient to show the utter weakness of the position of Lamarckism:--if their characteristics did not arise among the workers themselves, but were transmitted from the pre-social time, how does it happen that the queens and drones of every generation can give anew to the workers the characteristics which they themselves have long ago lost?" (p. 68).

It is curious to see put forward in so triumphant a manner, by a professed naturalist, a question so easily disposed of. I answer it by putting another. How does it happen that among those moths of which the female has but rudimentary wings, she continues to endow the males of her species with wings? How does it happen, for example, that among the _Geometridæ_, the peculiar structures and habits of which show that they have all descended from a common ancestor, some species have winged females and some wingless females; and that though they have lost the wings the ancestral females had, these wingless females convey to the males the normal developments of wings? Or, still better, how is it that in the _Psychidæ_ there are apterous worm-like females, which lay eggs that bring forth winged males of the ordinary imago form? If for males we read workers, the case is parallel to the cases of those social insects, the queens of which bequeath characteristics they have themselves lost. The ordinary facts of embryonic evolution yield us analogies. What is the most common trait in the development of the sexes? When the sexual organs of either become pronounced, the incipient ancillary organs belonging to the opposite sex cease to develop and remain rudiments, while the organs special to the sex, essential and nonessential, become fully developed. What, then, must happen with the queen-ant, which, through countless generations, has ceased to use certain structures and has lost them from disuse? If one of the eggs which she lays, capable, as Professor Weismann admits, of becoming queen, male, or worker of one or other kind, does not at a certain stage begin actively to develop its reproductive system, then those organs of the ancestral or pre-social type which the queen has lost begin to develop, and a worker results.

Another difficulty in the way of my view, supposed to be fatal, is that presented by the Honey-ants--aberrant members of certain ant-colonies which develop so enormously the pouch into which the food is drawn, that the abdomen becomes little else than a great bladder out of which the head, thorax, and legs protrude. This, it is thought, cannot be accounted for otherwise than as a consequence of specially endowed eggs, which it has become profitable to the community for the queen to produce. But the explanation fits in quite easily with the view I have set forth. No one will deny that the taking in of food is the deepest of vital requirements, and the correlative instinct a dominant one; nor will any one deny that the instinct of feeding young is less deeply seated--comes later in order of time. So, too, every one will admit that the worker-bee or worker-ant before regurgitating food into the mouth of a larva must first of all take it in. Hence, alike in order of time and necessity, it is to be assumed that development of the nervous structures which guide self-nutrition, precedes development of the nervous structures which guide the feeding of larvæ. What, then, will in some cases happen, supposing there is an arrested development consequent on innutrition? It will in some cases happen that while the nervous centres prompting and regulating deglutition are fully formed, the formation of those prompting and regulating the regurgitation of the food into the mouths of larvæ are arrested. What will be the consequence? The life of the worker is mainly passed in taking in food and putting it out again. If the putting out is stopped its life will be mainly passed in taking in food. The receptacle will go on enlarging and it will eventually assume the monstrous form that we see.[137]

Here, however, to exclude misinterpretations, let me explain. I by no means deny that variation and selection have produced, in these insect-communities, certain effects such as Mr. Darwin suggested. Doubtless ant-queens vary; doubtless there are variations in their eggs; doubtless differences of structure in the resulting progeny sometimes prove advantageous to the stirp, and originate slight modifications of the species. But such changes, legitimately to be assumed, are changes in single parts--in single organs or portions of organs. Admission of this does not involve admission that there can take place numerous correlated variations in different and often remote parts, which must take place simultaneously or else be useless. Assumption of this is what Professor Weismann's argument requires, and assumption of this we have seen to be absurd.

Before leaving the general problem presented by the social insects, let me remark that the various complexities of action not explained by inheritance from pre-social or semi-social types, are probably due to accumulated and transmitted knowledge. I recently read an account of the education of a butterfly, carried to the extent that it became quite friendly with its protector and would come to be fed. If a non-social and relatively unintelligent insect is capable of thus far consciously adjusting its actions, then it seems a reasonable supposition that in a community of social insects there has arisen a mass of experience and usage into which each new individual is initiated; just as happens among ourselves. We have only to consider the chaos which would result were we suddenly bereft of language, and if the young were left to grow up without precept and example, to see that very probably the polity of an insect community is made possible by the addition of intelligence to instinct, and the transmission of information through sign-language.

* * * * *

There remains now the question of _panmixia_, which stands exactly where it did when I published the "Rejoinder to Professor Weismann."

After showing that the interpretation I put upon his view was justified by certain passages quoted; and after pointing out that one of his adherents had set forth the view which I combated--if not as his view yet as supplementary to it; I went on to criticize the view as set forth afresh by Professor Weismann himself. I showed that as thus set forth the actuality of the supposed cause of decrease in disused organs, implies that _minus_ variations habitually exceed _plus_ variations--in degree or in number, or in both. Unless it can be proved that such an excess ordinarily occurs, the hypothesis of _panmixia_ has no place; and I asked, where is the proof that it occurs.

No reply.

Not content with this abstract form of the question I put it also in a concrete form, and granted for the nonce Professor Weismann's assumption: taking the case of the rudimentary hind limbs of the whale. I said that though, during those early stages of decrease in which the disused limbs were external, natural selection probably had a share in decreasing them, since they were then impediments to locomotion, yet when they became internal, and especially when they had dwindled to nothing but remnants of the femurs, it is impossible to suppose that natural selection played any part: no whale could have survived and initiated a more prosperous stirp in virtue of the economy achieved by such a decrease. The operation of natural selection being out of the question, I inquired whether such a decrease, say of one-half when the femurs weighed a few ounces, occurring in one individual, could be supposed in the ordinary course of reproduction to affect the whole of the whale species inhabiting the Arctic Seas and the North Atlantic Ocean; and so on with successive diminutions until the rudiments had reached their present minuteness. I asked whether such an interpretation could be rationally entertained.

No reply.

Now in the absence of replies to these two questions it seems to me that the verdict must go against Professor Weismann by default. If he has to surrender the hypothesis of _panmixia_, what results? All that evidence collected by Mr. Darwin and others, regarded by them as proof of the inheritance of acquired characters, which was cavalierly set aside on the strength of this alleged process of panmixia, is reinstated. And this reinstated evidence, joined with much evidence since furnished, suffices to establish the repudiated interpretation.

In the printed report of his Romanes Lecture, after fifty pages of complicated speculations which we are expected to accept as proofs, Professor Weismann ends by saying, in reference to the case of the neuter insects:--

"This case is of additional interest, as it may serve to convince those naturalists who are still inclined to maintain that acquired characters are inherited, and to support the Lamarckian principle of development, that their view cannot be the right one. It has not proved tenable in a single instance" (p. 54).

Most readers of the foregoing pages will think that since Professor Weismann has left one after another of my chief theses without reply, this is rather a strong assertion; and they will still further raise their eyebrows on remembering that, as I have shown, where he has given answers his answers are invalid.

* * * * *

And now we come to the additions which I indicated at the outset as having to be made--certain evidences which have come to light since this controversy commenced.

When, by a remembered observation made in boyhood, joined with the familiar fact that worker-larvæ can be changed into the larvæ of queens by feeding, I was led to suggest that probably all the variations of form in the social insects are consequent on differences of nurture, I was unaware that observations and experiments were being made which have justified this suggestion. Professor Grassi has recently published accounts of the food-habits of two European species of Termites, shewing that the various forms are due to feeding. He is known to be a most careful observer, and some of the most curious of his facts are confirmed by the collection of white ants exhibited by Dr. David Sharp, F.R.S., at the _soirée_ of the Royal Society in May last. He has favoured me with the following account of Grassi's results, which I publish with his assent:--

"There is great variety as to the constituents of the community and economy of the species in White Ants. One of the simplest conditions known is that studied by Grassi in the case of the European species Calotermes flavicollis. In this species there is no worker caste; the adult forms are only of two kinds, viz., soldiers, and the males and females; the sexes are externally almost indistinguishable, and there are males and females of soldiers as well as of the winged forms, though the sexual organs do not undergo their full development in any soldier whether male or female.

"The soldier is not however a mere instance of simple arrested development. It is true that there is in it arrested development of the sexual organs, but this is accompanied by change of form of other parts--changes so extreme that one would hardly suppose the soldier to have any connection with either the young or the adult of the winged forms.

"Now according to Grassi the whole of the individuals when born are undifferentiated forms (except as to sex), and each one is capable of going on the natural course of development and thus becoming a winged insect, or can be deviated from this course and made into a soldier; this is accomplished by the White Ants by special courses of feeding.

"The evidence given by Grassi is not conclusive as to the young being all born alike; and it may be that there are some individuals born that could not be deviated from the natural course and made into soldiers. But there is one case which seems to show positively that the deviation Grassi believes to occur is real, and not due to the selection by the ants of an individual that though appearing to our eyes undifferentiated is not really so. This is that an individual can be made into a soldier after it has visibly undergone one half or more of the development into a winged form. The Termites can in fact operate on an individual that has already acquired the rudiments of wings and whose head is totally destitute of any appearance of the shape of the armature peculiar to the soldier, and can turn it into a soldier; the rudiments of the wings being in such a case nearly entirely re-absorbed."

Grassi has been for many years engaged in investigating these phenomena, and there is no reason for rejecting his statement. We can scarcely avoid accepting it, and if so, Professor Weismann's hypothesis is conclusively disposed of. Were there different sets of "determinants" for the soldier-form and for the winged sexual form, those "determinants" which had gone a long way towards producing the winged sexual form, would inevitably go on to complete that form, and could not have their proclivity changed by feeding.

[Yet more evidence to the like effect has since become known. At the meeting of the Entomological Society, on March 14, 1894 (reported in _Nature_, March 29):--

"Dr. D. Sharp, F.R.S., exhibited a collection of white ants (_Termites_), formed by Mr. G. D. Haviland in Singapore, which comprised about twelve species, of most of which the various forms were obtained. He said that Prof. Grassi had recently made observations on the European species, and had brought to light some important particulars; and also that in the discussion that had recently been carried on between Mr. Herbert Spencer and Prof. Weismann, the former had stated that in his opinion the different forms of social insects were produced by nutrition. Prof. Grassi's observations showed this view to be correct, and the specimens now exhibited confirmed one of the most important points in his observations. Dr. Sharp also stated that Mr. Haviland found in one nest eleven neoteinic queens--that is to say, individuals having the appearance of the queen in some respects, while in others they are still immature."

Another similarly conclusive verification I published in _Nature_ for December 6, 1894, under the title "The Origin of Classes among the 'Parasol' Ants." The letter ran as follows:--

"Mr. J. H. Hart is Superintendent of the Royal Botanic Gardens in Trinidad. He has sent me a copy of his report presented to the Legislative Council in March, 1893, and has drawn my attention to certain facts contained in it concerning the 'Parasol' ants--the leaf-cutting ants which feed on the fungi developed in masses of the cut leaves carried to their nests. Both Mr. Bates and Mr. Belt described these ants, but described, it seems, different, though nearly allied, species, the habits of which are partially unlike. As they are garden-pests, Mr. Hart was led to examine into the development and social arrangements of these ants; establishing, to that end, artificial nests, after the manner adopted by Sir John Lubbock. Several of the facts set down have an important bearing on a question now under discussion. The following extracts, in which they are named, I abridge by omitting passages not relevant to the issue:--

"'The history of my nests is as follows: Nos. 1 and 2 were both taken (August 9) on the same day, while destroying nests in the Gardens, and were portions of separate nests but of the same species. No. 3 was procured on September 5, and is evidently a different although an allied species to Nos. 1 and 2.

"'Finding neither of my nests had a queen, I procured one from another nest about to be destroyed, and placed it with No. 1 nest. It was received by the workers, and at once attended by a numerous retinue in royal style. On August 30 I removed the queen from No. 1 and placed it with No. 2, when it was again received in a most loyal manner....

"'Ants taken from Nos. 1 and 2 and placed with No. 3 were immediately destroyed by the latter, and even the soldiers of No. 3, as well as workers or nurses, were destroyed when placed with Nos. 1 and 2.

"'In nest No. 2, from which I removed the queen on August 30, there are now in the pupa stage several queens and several males. The forms of ant in nests Nos. 1 and 2 are as follows: (_a_) queen, (_b_) male (both winged, but the queen loses its wings after marital flight), (_c_) large workers, (_d_) small workers, and (_e_) nurses. In nest No. 3 I have not yet seen the queen or male, but it possesses--(_a_) soldier, (_b_) larger workers, (_c_) smaller workers, and (_d_) nurses; but these are different in form to those of nests No. 1 and No. 2. Probably we might add a third form of worker, as there are several sizes in the nest....

"'It is curious that in No. 1 nest, from which the queen was removed on August 30, new queens and males are now being developed, while in No. 2 nest, where the queen is at present, nothing but workers have been brought out, and if a queen larva or pupa is placed there it is at once destroyed, while worker larvæ or pupæ are amicably received. In No. 3 all the eggs, larvæ, and pupæ collected with the nest have been hatched, and no eggs have since made their appearance to date. There is no queen with this nest.... On November 14 I attempted to prove by experiment how small a number of "parasol" ants it required to form a new colony. I placed two dozen of ants (one dozen workers and one dozen nurses) in two separate nests, No. 4 and No. 5. With No. 4 I placed a few larvæ with a few rose petals for them to manipulate. With No. 5 I gave a small piece of nest covered with mycelium. On the 16th these nests were destroyed by small foraging ants, known as the "sugar" or "meat" ant, and I had to remove them and replace with a new colony. My notes on these are not sufficiently lengthy to be of much importance. But I noted four eggs laid on the 16th, or two days after being placed in their new quarters; no queen being present. The experiment is being continued. I may mention that in No. 4 nest, in which no fungus was present, the larvæ of all sizes appeared to change into the pupæ stage at once for want of food [a fact corresponding with the fact I have named as observed by myself sixty years ago in the case of wasp larvæ]. The circumstance tends to show that the development of the insect is influenced entirely by the feeding it gets in the larva stage.

"'In nest No. 2 before the introduction of a queen there were no eggs or larvæ. The first worker was hatched on October 27, or fifty-seven days afterwards, and a continual succession has since been maintained, but as yet (November 19) no males or queens have made their appearance.'

"In a letter accompanying the report, Mr. Hart says:--

"'Since these were published, my notes go to prove that ants can practically manufacture at will, male, female, soldier, worker, or nurse. Some of the workers are capable of laying eggs, and from these can be produced all the various forms as well as from a queen's egg.

"'There does not, however, appear to be any difference in the character of the food; as I cannot find that the larger larvæ are fed with anything different to that given to the smaller.'

"These results were obtained before the recent discussion of the question commenced, and joined with the other evidence entirely dispose of those arguments which Prof. Weismann bases on facts furnished by the social insects."]

The other piece of additional evidence I have referred to, is furnished by two papers contributed to _The Journal of Anatomy and Physiology_ for October 1893 and April 1894, by R. Havelock Charles, M. D., &c. &c., Professor of Anatomy in the Medical College, Lahore. These papers set forth the differences between the leg-bones of Europeans and those of the Punjaub people--differences caused by their respective habits of sitting in chairs and squatting on the ground. He enumerates more than twenty such differences, chiefly in the structures of the knee-joint and ankle-joint. From the _résumé_ of his second paper I quote the following passages, which sufficiently show the data and the inferences:--

"7. The habits as to sitting postures of Europeans differ from those of their prehistoric ancestors, the Cave-dwellers, &c., who probably squatted on the ground.

"8. The sitting postures of Orientals are the same now as ever. They have retained the habits of their ancestors. The Europeans have not done so.

"9. Want of use would induce changes in form and size, and so, gradually, small differences would be integrated till there would be total disappearance of the markings on the European skeleton, as no advantage would accrue to him from the possession of facets on his bones fitting them for postures not practised by him.

"10. The facets seen on the bones of the Panjabi infant or foetus have been transmitted to it by the accumulation of peculiarities gained by habit in the evolution of its racial type--in which an acquisition having become a permanent possession, 'profitable to the individual under its conditions of life,' is transmitted as a useful inheritance.

"11. These markings are due to the influence of certain positions, which are brought about by the use of groups of muscles, and they are the definite results produced by actions of these muscles.

"12. The effects of the use of the muscles mentioned in No. 11 are transmitted to the offspring, for the markings are present in the _foetus-in-utero_, in the child at birth, and in the infant.

"13. The markings are instances of the transmission of acquired characters, which heritage in the individual, function subsequently develops."

No other conclusion appears to me possible. _Panmixia_, even were it not invalidated by its unwarranted assumption as above shown, would be out of court: the case is not a case of either increase or decrease of size but of numerous changes of form. Simultaneous variation of co-operative parts cannot be alleged, since these co-operative parts have not changed in one way but in various ways and degrees. And even were it permissible to suppose that the required different variations had taken place simultaneously, natural selection cannot be supposed to have operated. The assumption would imply that in the struggle for existence, individuals of the European races who were less capable than others of crouching and squatting, gained by those minute changes of structure which incapacitated them, such advantages that their stirps prevailed over other stirps--an absurd supposition.

And now I must once more point out that a grave responsibility rests on biologists in respect of the general question; since wrong answers lead, among other effects, to wrong beliefs about social affairs and to disastrous social actions. In me this conviction has unceasingly strengthened. Though _The Origin of Species_ proved to me that the transmission of acquired characters cannot be the sole factor in organic evolution, as I had assumed in _Social Statics_ and in _The Principles of Biology_, published in pre-Darwinian days, yet I have never wavered in the belief that it is a factor and an all-important factor. And I have felt more and more that since all the higher sciences are dependent on the science of life, and must have their conclusions vitiated if a fundamental datum given to them by the teachers of this science is erroneous, it behoves these teachers not to let an erroneous datum pass current: they are called on to settle this vexed question one way or other. The times give proof. The work of Mr. Benjamin Kidd on _Social Evolution_, which has been so much lauded, takes Weismannism as one of its data; and if Weismannism be untrue, the conclusions Mr. Kidd draws must be in large measure erroneous and may prove mischievous.

POSTSCRIPT.--Since the foregoing pages have been put in type there has appeared in _Natural Science_ for September, an abstract of certain parts of a pamphlet by Professor Oscar Hertwig, setting forth facts directly bearing on Professor Weismann's doctrine respecting the distinction between reproductive cells and somatic cells. In _The Principles of Biology_, § 77, I contended that reproductive cells differ from other cells composing the organism, only in being unspecialized. And in support of the hypothesis that tissue-cells in general have a reproductive potentiality, I instanced the cases of the _Begonia phyllomaniaca_ and _Malaxis paludosa_. In the thirty years which have since elapsed, many facts of like significance have been brought to light, and various of these are given by Professor Hertwig. Here are some of them:--

"Galls are produced under the stimulus of the insect almost anywhere on the surface of a plant. Yet in most cases these galls, in a sense grown at random on the surface of a plant, when placed in damp earth will give rise to a young plant. In the hydroid _Tubularia mesembryanthemum_, when the polyp heads are cut off, new heads arise. But if both head and root be cut off, and the upper end be inserted in the mud, then from the original upper end not head-polyps but root filaments will arise, while from the original lower end not root filaments but head-polyps will grow.... Driesch, by separating the first two and the first four segmentation spheres of an _Echinus_ ovum, obtained two or four normal plutei, respectively one half and a quarter of the normal size.... So, also, in the case of _Amphioxus_, Wilson obtained a normal, but proportionately diminished embryo with complete nervous system from a separated sphere of a two- or four- or eight celled stage.... Chabry obtained normal embryos in cases where some of the segmentation-spheres had been artificially destroyed."

These evidences, furnished by independent observers, unite in showing, firstly, that all the multiplying cells of the developing embryo are alike; and, secondly, that the soma-cells of the adult severally retain, in a latent form, all the powers of the original embryo-cell. If these facts do not disprove absolutely Professor Weismann's hypothesis, we may wonderingly ask what facts would disprove it?

Since Hertwig holds that all the cells forming an organism of any species primarily consist of the same components, I at first thought that his hypothesis was identical with my own hypothesis of "physiological units," or, as I would now call them, constitutional units. It seems otherwise, however; for he thinks that each cell contains "only those material particles which are bearers of cell-properties," and that organs "are the functions of cell-complexes." To this it may be replied that the ability to form the appropriate cell-complexes, itself depends upon the constitutional units contained in the cells.

APPENDIX C.

THE INHERITANCE OF FUNCTIONALLY-WROUGHT MODIFICATIONS: A SUMMARY.

The assertion that changes of structure caused by changes of function are transmitted to descendants is continually met by the question--Where is the evidence? When some facts are assigned in proof, they are pooh-poohed as insufficient. If after a time the question is raised afresh and other facts are named, there is a like supercilious treatment of them. Successively rejected in this way, the evidences do not accumulate in the minds of opponents; and hence produce little or no effect. When they are brought together, however, it turns out that they are numerous and weighty. We will group them into negative and positive.

* * * * *

Negative evidence is furnished by those cases in which traits otherwise inexplicable are explained if the structural effects of use and disuse are transmitted. In the foregoing chapters and appendices three have been given.

(1) Co-adaptation of co-operative parts comes first. This has been exemplified by the case of enlarged horns in a stag, by the case of an animal led into the habit of leaping, and in the case of the giraffe (cited in "The Factors of Organic Evolution"); and it has been shown that the implied co-adaptations of parts cannot possibly have been effected by natural selection.

(2) The possession of unlike powers of discrimination by different parts of the human skin, was named as a problem to be solved on the hypothesis of natural selection or the hypothesis of panmixia; and it was shown that neither of these can by any twisting yield a solution. But the facts harmonize with the hypothesis that the effects of use are inherited.

(3) Then come the cases of those rudimentary organs which, like the hind limbs of the whale, have nearly disappeared. Dwindling by natural selection is here out of the question; and dwindling by panmixia, even were its assumptions valid, would be incredible. But as a sequence of disuse the change is clearly explained.

Failure to solve any _one_ of these three problems would, I think, alone prove the Neo-Darwinian doctrines untenable; and the fact that we have _three_ unsolved problems seems to me fatal.

* * * * *

From this negative evidence, turn now to the positive evidence. This falls into several groups.

There are first the facts collected by Mr. Darwin, implying functionally-altered structures in domestic animals. The hypothesis of panmixia is, as we have seen, out of court; and therefore Mr. Darwin's groups of evidences are reinstated. There is the changed ratio of wing-bones and leg-bones in the duck; there are the drooping ears of cats in China, of horses in Russia, of sheep in Italy, of guinea-pigs in Germany, of goats and cattle in India, of rabbits, pigs, and dogs in all long-civilized countries. Though artificial selection has come into play where drooping has become a curious trait (as in rabbits), and has probably caused the greater size of ears which has in some cases gone along with diminished muscular power over them; yet it could not have been the initiator, and has not been operative on animals bred for profit. Again there are the changes produced by climate; as instance, among plants, the several varieties of maize established in Germany and transformed in the course of a few generations.

Facts of another class are yielded by the blind inhabitants of caverns. One who studies the memoir by Mr. Packard on _The Cave Fauna of North America_, &c., will be astonished at the variety of types in which degeneration or loss of the eyes has become a concomitant of life passed in darkness. A great increase in the force of this evidence will be recognized on learning that absence or extreme imperfection of visual organs is found also in creatures living in perpetual night at the bottoms of deep oceans. Endeavours to account for these facts otherwise than by the effects of disuse we have seen to be futile.

Kindred evidence is yielded by decrease of the jaws in those races which have had diminished use of them--mankind and certain domestic animals. Relative smallness in the jaws of civilized men, manifest enough on comparison, has been proved by direct measurement. In pet dogs--pugs, household spaniels--we find associated the same cause with the same effect. Though there has been artificial selection, yet this did not operate until the diminution had become manifest. Moreover there has been diminution of the other structures concerned in biting: there are smaller muscles, feeble zygomata, and diminished areas for insertion of muscles--traits which cannot have resulted from selection, since they are invisible in the living animal.

In abnormal vision produced by abnormal use of the eyes we have evidence of another kind. That the Germans, among whom congenital short sight is notoriously prevalent, have been made shortsighted by inheritance of modifications due to continual reading of print requiring close attention, is by some disputed. It is strange, however, that if there exists no causal connexion between them, neither trait occurs without the other elsewhere. But for the belief that there is a causal connexion we have the verifying testimony of oculists. From Dr. Lindsay Johnson I have cited cases within his professional experience of functionally-produced myopia transmitted to children; and he asserts that other oculists have had like experiences.

Development of the musical faculty in the successive members of families from which the great composers have come, as well as in the civilized races at large, is not to be explained by natural selection. Even when it is great, the musical faculty has not a life-saving efficiency as compared with the average of faculties; for the most highly gifted have commonly passed less prosperous lives and left fewer offspring than have those possessed of ordinary abilities. Still less can it be said that the musical faculty in mankind at large has been developed by survival of the fittest. No one will assert that men in general have been enabled to survive and propagate in proportion as their musical appreciation was great.

The transmission of nervous peculiarities functionally produced is alleged by the highest authorities--Dr. Savage, president of the Neurological Society, and Dr. Hughlings Jackson. The evidence they assign confirms, and is confirmed by, that which the development of the musical faculty above named supplies.

Here, then, we have sundry groups of facts directly supporting the belief that functionally-wrought modifications descend from parents to offspring.

* * * * *

Now let us consider the position of those Darwinians who dissent from Darwin, and who make light of all this evidence. We might naturally suppose that their own hypothesis is unassailable. Yet, strange to say, they admit that there is no direct proof that any species has been established by natural selection. The proof is inferential only.

The certainty of an axiom does not give certainty to the deductions drawn from it. That natural selection is, and always has been, operative is incontestable. Obviously I should be the last person to deny that survival of the fittest is a necessity: its negation is inconceivable. The Neo-Darwinians, however, judging from their attitude, apparently assume that firmness of the basis implies firmness of the superstructure. But however high may be the probability of some of the conclusions drawn, none of them can have more than probability; while some of them remain, and are likely to remain, very questionable. Observe the difficulties.

(1) The general argument proceeds upon the analogy between natural selection and artificial selection. Yet all know that the first cannot do what the last does. Natural selection can do nothing more than preserve those of which the _aggregate_ characters are most favourable to life. It cannot pick out those possessed of one particular favourable character, unless this is of extreme importance.

(2) In many cases a structure is of no service until it has reached a certain development; and it remains to account for that increase of it by natural selection which must be supposed to take place before it reaches the stage of usefulness.

(3) Advantageous variations, not preserved in nature as they are by the breeder, are liable to be swamped by crossing or to disappear by atavism.

Now whatever replies are made, their component propositions cannot be necessary truths. So that the conclusion in each case, however reasonable, cannot claim certainty: the fabric can have no stability like that of its foundation.

When to uncertainties in the arguments supporting the hypothesis we add its inability to explain facts of cardinal significance, as proved above, there is I think ground for asserting that natural selection is less clearly shown to be a factor in the origination of species than is the inheritance of functionally-wrought changes.

* * * * *

If, finally, it is said that the mode in which functionally-wrought changes, especially in small parts, so affect the reproductive elements as to repeat themselves in offspring, cannot be imagined--if it be held inconceivable that those minute changes in the organs of vision which cause myopia can be transmitted through the appropriately-modified sperm-cells or germ-cells; then the reply is that the opposed hypothesis presents a corresponding inconceivability. Grant that the habit of a pointer was produced by selection of those in which an appropriate variation in the nervous system had occurred; it is impossible to imagine how a slightly-different arrangement of a few nerve-cells and fibres could be conveyed by a spermatozoon. So too it is impossible to imagine how in a spermatozoon there can be conveyed the 480,000 independent variables required for the construction of a single peacock's feather, each having a proclivity towards its proper place. Clearly the ultimate process by which inheritance is effected in either case passes comprehension; and in this respect neither hypothesis has an advantage over the other.

APPENDIX D.

ON ALLEGED "SPONTANEOUS GENERATION," AND ON THE HYPOTHESIS OF PHYSIOLOGICAL UNITS.

[_The following letter, originally written for publication in the_ North American Review, _but declined by the Editor in pursuance of a general rule, and eventually otherwise published in the United States, I have thought well to append to this first volume of the_ Principles of Biology. _I do this because the questions which it discusses are dealt with in this volume; and because the further explanations it furnishes seem needful to prevent misapprehensions._]

_The Editor of the North American Review._

SIR,

It is in most cases unwise to notice adverse criticisms. Either they do not admit of answers or the answers may be left to the penetration of readers. When, however, a critic's allegations touch the fundamental propositions of a book, and especially when they appear in a periodical having the position of the _North American Review_, the case is altered. For these reasons the article on "Philosophical Biology," published in your last number, demands from me an attention which ordinary criticisms do not.

It is the more needful for me to notice it, because its two leading objections have the one an actual fairness and the other an apparent fairness; and in the absence of explanations from me, they will be considered as substantiated even by many, or perhaps most, of those who have read the work itself--much more by those who have not read it. That to prevent the spread of misapprehensions I ought to say something, is further shown by the fact that the same two objections have already been made in England--the one by Dr. Child, of Oxford, in his _Essays on Physiological Subjects_, and the other by a writer in the _Westminster Review_ for July, 1865.

* * * * *

In the note to which your reviewer refers, I have, as he says, tacitly repudiated the belief in "spontaneous generation;" and that I have done this in such a way as to leave open the door for the interpretation given by him is true. Indeed the fact that Dr. Child, whose criticism is a sympathetic one, puts the same construction on this note, proves that your reviewer has but drawn what seems to be a necessary inference. Nevertheless, the inference is one which I did not intend to be drawn.

In explanation, let me at the outset remark that I am placed at a disadvantage in having had to omit that part of the System of Philosophy which deals with Inorganic Evolution. In the original programme will be found a parenthetic reference to this omitted part, which should, as there stated, precede the _Principles of Biology_. Two volumes are missing. The closing chapter of the second, were it written, would deal with the evolution of organic matter--the step preceding the evolution of living forms. Habitually carrying with me in thought the contents of this unwritten chapter, I have, in some cases, expressed myself as though the reader had it before him; and have thus rendered some of my statements liable to misconstructions. Apart from this, however, the explanation of the apparent inconsistency is very simple, if not very obvious. In the first place, I do not believe in the "spontaneous generation" commonly alleged, and referred to in the note; and so little have I associated in thought this alleged "spontaneous generation" which I disbelieve, with the generation by evolution which I do believe, that the repudiation of the one never occurred to me as liable to be taken for repudiation of the other. That creatures having _quite specific structures_ are evolved in the course of a few hours, without antecedents calculated to determine their specific forms, is to me incredible. Not only the established truths of Biology, but the established truths of science in general, negative the supposition that organisms having structures definite enough to identify them as belonging to known genera and species, can be produced in the absence of germs derived from antecedent organisms of the same genera and species. If there can suddenly be imposed on simple protoplasm the organization which constitutes it a _Paramoecium_, I see no reason why animals of greater complexity, or indeed of any complexity, may not be constituted after the same manner. In brief, I do not accept these alleged facts as exemplifying Evolution, because they imply something immensely beyond that which Evolution, as I understand it, can achieve. In the second place, my disbelief extends not only to the alleged cases of "spontaneous generation," but to every case akin to them. The very conception of spontaneity is wholly incongruous with the conception of Evolution. For this reason I regard as objectionable Mr. Darwin's phrase "spontaneous variation" (as indeed he does himself); and I have sought to show that there are always assignable causes of variation. No form of Evolution, inorganic or organic, can be spontaneous; but in every instance the antecedent forces must be adequate in their quantities, kinds, and distributions, to work the observed effects. Neither the alleged cases of "spontaneous generation," nor any imaginable cases in the least allied to them, fulfil this requirement.

If, accepting these alleged cases of "spontaneous generation," I had assumed, as your reviewer seems to do, that the evolution of organic life commenced in an analogous way; then, indeed, I should have left myself open to a fatal criticism. This supposed "spontaneous generation" habitually occurs in menstrua that contain either organic matter, or matter originally derived from organisms; and such organic matter, proceeding in all known cases from organisms of a higher kind, implies the pre-existence of such higher organisms. By what kind of logic, then, is it inferrible that organic life was initiated after a manner like that in which _Infusoria_ are said to be now spontaneously generated? Where, before life commenced, were the superior organisms from which these lowest organisms obtained their organic matter? Without doubting that there are those who, as the reviewer says, "can penetrate deeper than Mr. Spencer has done into the idea of universal evolution," and who, as he contends, prove this by accepting the doctrine of "spontaneous generation"; I nevertheless think that I can penetrate deep enough to see that a tenable hypothesis respecting the origin of organic life must be reached by some other clue than that furnished by experiments on decoction of hay and extract of beef.

From what I do not believe, let me now pass to what I do believe. Granting that the formation of organic matter, and the evolution of life in its lowest forms, may go on under existing cosmical conditions; but believing it more likely that the formation of such matter and such forms, took place at a time when the heat of the Earth's surface was falling through those ranges of temperature at which the higher organic compounds are unstable; I conceive that the moulding of such organic matter into the simplest types, must have commenced with portions of protoplasm more minute, more indefinite, and more inconstant in their characters, than the lowest Rhizopods--less distinguishable from a mere fragment of albumen than even the _Protogenes_ of Professor Haeckel. The evolution of specific shapes must, like all other organic evolution, have resulted from the actions and reactions between such incipient types and their environments, and the continued survival of those which happened to have specialities best fitted to the specialities of their environments. To reach by this process the comparatively well-specialized forms of ordinary _Infusoria_, must, I conceive, have taken an enormous period of time.

To prevent, as far as may be, future misapprehension, let me elaborate this conception so as to meet the particular objections raised. The reviewer takes for granted that a "first organism" must be assumed by me, as it is by himself. But the conception of a "first organism," in anything like the current sense of the words, is wholly at variance with conception of evolution; and scarcely less at variance with the facts revealed by the microscope. The lowest living things are not properly speaking organisms at all; for they have no distinctions of parts--no traces of organization. It is almost a misuse of language to call them "forms" of life: not only are their outlines, when distinguishable, too unspecific for description, but they change from moment to moment and are never twice alike, either in two individuals or in the same individual. Even the word "type" is applicable in but a loose way; for there is little constancy in their generic characters: according as the surrounding conditions determine, they undergo transformations now of one kind and now of another. And the vagueness, the inconstancy, the want of appreciable structure, displayed by the simplest of living things as we now see them, are characters (or absences of characters) which, on the hypothesis of Evolution, must have been still more decided when, as at first, no "forms," no "types," no "specific shapes," had been moulded. That "absolute commencement of organic life on the globe," which the reviewer says I "cannot evade the admission of," I distinctly deny. The affirmation of universal evolution is in itself the negation of an "absolute commencement" of anything. Construed in terms of evolution, every kind of being is conceived as a product of modifications wrought by insensible gradations on a pre-existing kind of being; and this holds as fully of the supposed "commencement of organic life" as of all subsequent developments of organic life. It is no more needful to suppose an "absolute commencement of organic life" or a "first organism," than it is needful to suppose an absolute commencement of social life and a first social organism. The assumption of such a necessity in this last case, made by early speculators with their theories of "social contracts" and the like, is disproved by the facts; and the facts, so far as they are ascertained, disprove the assumption of such a necessity in the first case. That organic matter was not produced all at once, but was reached through steps, we are well warranted in believing by the experiences of chemists. Organic matters are produced in the laboratory by what we may literally call _artificial evolution_. Chemists find themselves unable to form these complex combinations directly from their elements; but they succeed in forming them indirectly, by successive modifications of simpler combinations. In some binary compound, one element of which is present in several equivalents, a change is made by substituting for one of these equivalents an equivalent of some other element; so producing a ternary compound. Then another of the equivalents is replaced, and so on. For instance, beginning with ammonia, N H_{3}, a higher form is obtained by replacing one of the atoms of hydrogen by an atom of methyl, so producing methyl-amine, N (C H_{3} H_{2}); and then, under the further action of methyl, ending in a further substitution, there is reached the still more compound substance dimethyl-amine, N (C H_{3}) (C H_{3}) H. And in this manner highly complex substances are eventually built up. Another characteristic of their method is no less significant. Two complex compounds are employed to generate, by their action upon one another, a compound of still greater complexity: different heterogeneous molecules of one stage, become parents of a molecule a stage higher in heterogeneity. Thus, having built up acetic acid out of its elements, and having by the process of substitution described above, changed the acetic acid into propionic acid, and propionic into butyric, of which the formula is

{C(CH_{3})(CH_{3})H} {CO(HO) };

this complex compound, by operating on another complex compound, such as the dimethyl-amine named above, generates one of still greater complexity, butyrate of dimethyl-amine

{C(CH)(CH_{3})H} N(CH_{3})(CH_{3})H. {CO(HO) }

See, then, the remarkable parallelism. The progress towards higher types of organic molecules is effected by modifications upon modifications; as throughout Evolution in general. Each of these modifications is a change of the molecule into equilibrium with its environment--an adaptation, as it were, to new surrounding conditions to which it is subjected; as throughout Evolution in general. Larger, or more integrated, aggregates (for compound molecules are such) are successively generated; as throughout Evolution in general. More complex or heterogeneous aggregates are so made to arise, one out of another; as throughout Evolution in general. A geometrically-increasing multitude of these larger and more complex aggregates so produced, at the same time results; as throughout Evolution in general. And it is by the action of the successively higher forms on one another, joined with the action of environing conditions, that the highest forms are reached; as throughout Evolution in general.

When we thus see the identity of method at the two extremes--when we see that the general laws of evolution, as they are exemplified in known organisms, have been unconsciously conformed to by chemists in the artificial evolution of organic matter; we can scarcely doubt that these laws were conformed to in the natural evolution of organic matter, and afterwards in the evolution of the simplest organic forms. In the early world, as in the modern laboratory, inferior types of organic substances, by their mutual actions under fit conditions, evolved the superior types of organic substances, ending in organizable protoplasm. And it can hardly be doubted that the shaping of organizable protoplasm, which is a substance modifiable in multitudinous ways with extreme facility, went on after the same manner. As I learn from one of our first chemists, Prof. Frankland, _protein_ is capable of existing under probably at least a thousand isomeric forms; and, as we shall presently see, it is capable of forming, with itself and other elements, substances yet more intricate in composition, that are practically infinite in their varieties of kind. Exposed to those innumerable modifications of conditions which the Earth's surface afforded, here in amount of light, there in amount of heat, and elsewhere in the mineral quality of its aqueous medium, this extremely changeable substance must have undergone now one, now another, of its countless metamorphoses. And to the mutual influences of its metamorphic forms under favouring conditions, we may ascribe the production of the still more composite, still more sensitive, still more variously-changeable portions of organic matter, which, in masses more minute and simpler than existing _Protozoa_, displayed actions verging little by little into those called vital--actions which protein itself exhibits in a certain degree, and which the lowest known living things exhibit only in a greater degree. Thus, setting out with inductions from the experiences of organic chemists at the one extreme, and with inductions from the observations of biologists at the other extreme, we are enabled deductively to bridge the interval--are enabled to conceive how organic compounds were evolved, and how, by a continuance of the process, the nascent life displayed in these became gradually more pronounced. And this it is which has to be explained, and which the alleged cases of "spontaneous generation" would not, were they substantiated, help us in the least to explain.

It is thus manifest, I think, that I have not fallen into the alleged inconsistency. Nevertheless, I admit that your reviewer was justified in inferring this inconsistency; and I take blame to myself for not having seen that the statement, as I have left it, is open to misconstruction.

* * * * *

I pass now to the second allegation--that in ascribing to certain specific molecules, which I have called "physiological units," the aptitude to build themselves into the structure of the organism to which they are peculiar, I have abandoned my own principle, and have assumed something beyond the re-distribution of Matter and Motion. As put by the reviewer, his case appears to be well made out; and that he is not altogether unwarranted in so putting it, may be admitted. Nevertheless, there does not in reality exist the supposed incongruity.

Before attempting to make clear the adequacy of the conception which I am said to have tacitly abandoned as insufficient, let me remove that excess of improbability the reviewer gives to it, by the extremely-restricted meaning with which he uses the word mechanical. In discussing a proposition of mine he says:--

"He then cites certain remarks of Mr. Paget on the permanent effects wrought in the blood by the poison of scarlatina and small-pox, as justifying the belief that such a 'power' exists, and attributes the repair of a wasted tissue to 'forces analogous to those by which a crystal reproduces its lost apex.' (Neither of which phenomena, however, is explicable by mechanical causes.)"

Were it not for the deliberation with which this last statement is made, I should take it for a slip of the pen. As it is, however, I have no course left but to suppose the reviewer unaware of the fact that molecular actions of all kinds are now not only conceived as mechanical actions, but that calculations based on this conception of them, bring out the results that correspond with observation. There is no kind of re-arrangement among molecules (crystallization being one) which the modern physicist does not think of. and correctly reason upon, in terms of forces and motions like those of sensible masses. Polarity is regarded as a resultant of such forces and motions; and when, as happens in many cases, light changes the molecular structure of a crystal, and alters its polarity, it does this by impressing, in conformity with mechanical laws, new motions on the constituent molecules. That the reviewer should present the mechanical conception under so extremely limited a form, is the more surprising to me because, at the outset of the very work he reviews, I have, in various passages, based inferences on those immense extensions of it which he ignores; indicating, for example, the interpretation it yields of the inorganic chemical changes effected by heat, and the organic chemical changes effected by light (_Principles of Biology_, § 13).

Premising, then, that the ordinary idea of mechanical action must be greatly expanded, let us enter upon the question at issue--the sufficiency of the hypothesis that the structure of each organism is determined by the polarities of the special molecules, or physiological units, peculiar to it as a species, which necessitate tendencies towards special arrangements. My proposition and the reviewer's criticism upon it, will be most conveniently presented if I quote in full a passage of his from which I have already extracted some expressions. He says:--

"It will be noticed, however, that Mr. Spencer attributes the possession of these 'tendencies,' or 'proclivities,' to natural inheritance from ancestral organisms; and it may be argued that he thus saves the mechanist theory and his own consistency at the same time, inasmuch as he derives even the 'tendencies' themselves ultimately from the environment. To this we reply, that Mr. Spencer, who advocates the nebular hypothesis, cannot evade the admission of an absolute commencement of organic life on the globe, and that the 'formative tendencies,' without which he cannot explain the evolution of a single individual, could not have been inherited by the first organism. Besides, by his virtual denial of spontaneous generation, he denies that the first organism was evolved out of the inorganic world, and thus shuts himself off from the argument (otherwise plausible) that its 'tendencies' were ultimately derived from the environment."

This assertion is already in great measure disposed of by what has been said above. Holding that, though not "spontaneously generated," those minute portions of protoplasm which first displayed in the feeblest degree that changeability taken to imply life, were evolved, I am _not_ debarred from the argument that the "tendencies" of the physiological units are derived from the inherited effects of environing actions. If the conception of a "first organism" were a necessary one, the reviewer's objection would be valid. If there were an "absolute commencement" of life, a definite line parting organic matter from the simplest living forms, I should be placed in the predicament he describes. But as the doctrine of Evolution itself tacitly negatives any such distinct separation; and as the negation is the more confirmed by the facts the more we know of them; I do not feel that I am entangled in the alleged difficulty. My reply might end here; but as the hypothesis in question is one not easily conceived, and very apt to be misunderstood, I will attempt a further elucidation of it.

Much evidence now conspires to show that molecules of the substances we call elementary are in reality compound; and that, by the combination of these with one another, and re-combinations of the products, there are formed systems of systems of molecules, unimaginable in their complexity. Step by step as the aggregate molecules so resulting, grow larger and increase in heterogeneity, they become more unstable, more readily transformable by small forces, more capable of assuming various characters. Those composing organic matter transcend all others in size and intricacy of structure; and in them these resulting traits reach their extreme. As implied by its name _protein_, the essential substance of which organisms are built, is remarkable alike for the variety of its metamorphoses and the facility with which it undergoes them: it changes from one to another of its thousand isomeric forms on the slightest change of conditions. Now there are facts warranting the belief that though these multitudinous isomeric forms of protein will not unite directly with one another, yet they admit of being linked together by other elements with which they combine. And it is very significant that there are habitually present two other elements, sulphur and phosphorus, which have quite special powers of holding together many equivalents--the one being pentatomic and the other hexatomic. So that it is a legitimate supposition (justified by analogies) that an atom of sulphur may be a bond of union among half-a-dozen different isomeric forms of protein; and similarly with phosphorus. A moment's thought will show that, setting out with the thousand isomeric forms of protein, this makes possible a number of these combinations almost passing the power of figures to express. Molecules so produced, perhaps exceeding in size and complexity those of protein as those of protein exceed those of inorganic matter, may, I conceive, be the special units belonging to special kinds of organisms. By their constitution they must have a plasticity, or sensitiveness to modifying forces, far beyond that of protein; and bearing in mind not only that their varieties are practically infinite in number, but that closely allied forms of them, chemically indifferent to one another as they must be, may coexist in the same aggregate, we shall see that they are fitted for entering into unlimited varieties of organic structures.

The existence of such physiological units, peculiar to each species of organism, is not unaccounted for. They are evolved simultaneously with the evolution of the organisms they compose--they differentiate as fast as these organisms differentiate; and are made multitudinous in kind by the same actions which make the organism they compose multitudinous, in kind. This conception is clearly representable in terms of the mechanical hypothesis. Every physicist will endorse the proposition that in each aggregate there tends to establish itself an equilibrium between the forces exercised by all the units upon each and by each upon all. Even in masses of substance so rigid as iron and glass, there goes on a molecular re-arrangement, slow or rapid according as circumstances facilitate, which ends only when there is a complete balance between the actions of the parts on the whole and the actions of the whole on the parts: the implications being that every change in the form or size of the whole, necessitates some redistribution of the parts. And though in cases like these, there occurs only a polar re-arrangement of the molecules, without changes in the molecules themselves; yet where, as often happens, there is a passage from the colloid to the crystalloid state, a change of constitution occurs in the molecules themselves. These truths are not limited to inorganic matter: they unquestionably hold of organic matter. As certainly as molecules of alum have a form of equilibrium, the octahedron, into which they fall when the temperature of their solvent allows them to aggregate, so certainly must organic molecules of each kind, no matter how complex, have a form of equilibrium in which, when they aggregate, their complex forces are balanced--a form far less rigid and definite, for the reason that they have far less definite polarities, are far more unstable, and have their tendencies more easily modified by environing conditions. Equally certain is it that the special molecules having a special organic structure as their form of equilibrium, must be reacted upon by the total forces of this organic structure; and that, if environing actions lead to any change in this organic structure, these special molecules, or physiological units, subject to a changed distribution of the total forces acting upon them will undergo modification--modification which their extreme plasticity will render easy. By this action and reaction I conceive the physiological units peculiar to each kind of organism, to have been moulded along with the organism itself. Setting out with the stage in which protein in minute aggregates, took on those simplest differentiations which fitted it for differently-conditioned parts of its medium, there must have unceasingly gone on perpetual re-adjustments of balance between aggregates and their units--actions and reactions of the two, in which the units tended ever to establish the typical form produced by actions and reactions in all antecedent generations, while the aggregate, if changed in form by change of surrounding conditions, tended ever to impress on the units a corresponding change of polarity, causing them in the next generation to reproduce the changed form--their new form of equilibrium.

This is the conception which I have sought to convey, though it seems unsuccessfully, in the _Principles of Biology_; and which I have there used to interpret the many involved and mysterious phenomena of Genesis, Heredity, and Variation. In one respect only am I conscious of having so inadequately explained myself, as to give occasion for a misinterpretation--the one made by the _Westminster_ reviewer above referred to. By him, as by your own critic, it is alleged that in the idea of "inherent tendencies" I have introduced, under a disguise, the conception of "the archæus, vital principle, _nisus formativus_, and so on." This allegation is in part answered by the foregoing explanation. That which I have here to add, and did not adequately explain in the _Principles of Biology_, is that the proclivity of units of each order towards the specific arrangement seen in the organism they form, is not to be understood as resulting from their own structures and actions only; but as the product of these and the environing forces to which they are exposed. Organic evolution takes place only on condition that the masses of protoplasm formed of the physiological units, and of the assimilable materials out of which others like themselves are to be multiplied, are subject to heat of a given degree--are subject, that is, to the unceasing impacts of undulations of a certain strength and period; and, within limits, the rapidity with which the physiological units pass from their indefinite arrangement to the definite arrangement they presently assume, is proportionate to the strengths of the ethereal undulations falling upon them. In its complete form, then, the conception is that these specific molecules, having the immense complexity above described, and having correspondently complex polarities which cannot be mutually balanced by any simple form of aggregation, have, for the form of aggregation in which all their forces are equilibrated, the structure of the adult organism to which they belong; and that they are compelled to fall into this structure by the co-operation of the environing forces acting on them, and the forces they exercise on one another--the environing forces being the source of the _power_ which effects the re-arrangement, and the polarities of the molecules determining the _direction_ in which that power is turned. Into this conception there enters no trace of the hypothesis of an "archæus or vital principle;" and the principles of molecular physics fully justify it.

It is, however, objected that "the living body in its development presents a long succession of _differing_ forms; a continued series of changes for the whole length of which, according to Mr. Spencer's hypothesis, the physiological units must have an 'inherent tendency.' Could we more truly say of anything, 'it is unrepresentable in thought?'" I reply that if there is taken into account an element here overlooked, the process will not be found "unrepresentable in thought." This is the element of size or mass. To satisfy or balance the polarities of each order of physiological units, not only a certain structure of organism, but a certain size of organism is needed; for the complexities of that adult structure in which the physiological units are equilibrated, cannot be represented within the small bulk of the embryo. In many minute organisms, where the whole mass of physiological units required for the structure is present, the very thing _does_ take place which it is above implied _ought_ to take place. The mass builds itself directly into the complete form. This is so with _Acari_, and among the nematoid _Entozoa_. But among higher animals such direct transformations cannot happen. The mass of physiological units required to produce the size as well as the structure that approximately equilibrates them, is not all present, but has to be formed by successive additions--additions which in viviparous animals are made by absorbing, and transforming into these special molecules, the organizable materials directly supplied by the parent, and which in oviparous animals are made by doing the like with the organizable materials in the "food-yelk," deposited by the parent in the same envelope with the germ. Hence it results that, under such conditions, the physiological units which first aggregate into the rudiment of the future organism, do not form a structure like that of the adult organism, which, when of such small dimensions, does not equilibrate them. They distribute themselves so as partly to satisfy the chief among their complex polarities. The vaguely-differentiated mass thus produced cannot, however, be in equilibrium. Each increment of physiological units formed and integrated by it, changes the distribution of forces; and this has a double effect. It tends to modify the differentiations already made, bringing them a step nearer to the equilibrating structure; and the physiological units next integrated, being brought under the aggregate of polar forces exercised by the whole mass, which now approaches a step nearer to that ultimate distribution of polar forces which exists in the adult organism, are coerced more directly into the typical structure. Thus there is necessitated a series of compromises. Each successive form assumed is unstable and transitional: approach to the typical structure going on hand in hand with approach to the typical bulk.

Possibly I have not succeeded by this explanation, any more than by the original explanation, in making this process "representable in thought." It is manifestly untrue, however, that I have, as alleged, re-introduced under a disguise the conception of a "vital principle." That I interpret embryonic development in terms of Matter and Motion, cannot, I think, be questioned. Whether the interpretation is adequate, must be a matter of opinion; but it is clearly a matter of fact, that I have not fallen into the inconsistency asserted by your reviewer. At the same time I willingly admit that, in the absence of certain statements which I have now supplied, he was not unwarranted in representing my conception in the way that he has done.

----

NOTES

[1] Gross misrepresentations of this statement, which have been from time to time made, oblige me, much against my will, to add here an explanation of it. The last of these perversions, uttered in a lecture delivered at Belfast by the Rev. Professor Watts, D.D., is reported in the _Belfast Witness_ of December 18, 1874; just while a third impression of this work is being printed from the plates. The report commences as follows:--"Dr. Watts, after showing that on his own confession Spencer was indebted for his facts to Huxley and Hooker, who," &c., &c.

Wishing in this, as in other cases, to acknowledge indebtedness when conscious of it, I introduced the words referred to, in recognition of the fact that I had repeatedly questioned the distinguished specialists named, on matters beyond my knowledge, which were not dealt with in the books at my command. Forgetting the habits of antagonists, and especially theological antagonists, it never occurred to me that my expression of thanks to my friends for "information where my own was deficient," would be turned into the sweeping statement that I was indebted to them for my facts.

Had Professor Watts looked at the preface to the second volume (the two having been published separately, as the prefaces imply), he would have seen a second expression of my indebtedness "for their valuable criticisms, and for the trouble they have taken in _checking_ the numerous statements of fact on which the arguments proceed"--no further indebtedness being named. A moment's comparison of the two volumes in respect of their accumulations of facts, would have shown him what kind of warrant there was for his interpretation.

Doubtless the Rev. Professor was prompted to make this assertion by the desire to discredit the work he was attacking; and having so good an end in view, thought it needless to be particular about the means. In the art of dealing with the language of opponents, Dr. Watts might give lessons to Monsignor Capel and Archbishop Manning.

_December 28th, 1874._

[2] In this passage as originally written (in 1862) they were described as incondensible; since, though reduced to the density of liquids, they had not been liquefied.

[3] Here and hereafter the word "atom" signifies a unit of something classed as an element, because thus far undecomposed by us. The word must not be supposed to mean that which its derivation implies. In all probability it is not a simple unit but a compound one.

[4] The name hydro-carbons was here used when these pages were written, thirty-four years ago. It was the name then current. In this case, as in multitudinous other cases, the substitution of newer words and phrases for older ones, is somewhat misleading. Putting the thoughts of 1862 in the language of 1897 gives an illusive impression of recency.

[5] It will perhaps seem strange to class oxygen as a crystalloid. But inasmuch as the crystalloids are distinguished from the colloids by their atomic simplicity, and inasmuch as sundry gases are reducible to a crystalline state, we are justified in so classing it.

[6] The remark made by a critic to the effect that in a mammal higher temperature diminishes the rate of molecular change in the tissues, leads me to add that the exhalation I have alleged is prevented if the heat rises above the range of variation normal to the organism; since, then, unusually rapid pulsations with consequent inefficient propulsion of the blood, cause a diminished rate of circulation. To produce the effect referred to in the text, heat must be associated with dryness; for otherwise evaporation is not aided. General evidence supporting the statement I have made is furnished by the fact that the hot and dry air of the eastern deserts is extremely invigorating; by the fact that all the energetic and conquering races of men have come from the hot and dry regions marked on the maps as rainless; and by the fact that travellers in Africa comment on the contrast between the inhabitants of the hot and dry regions (relatively elevated) and those of the hot and moist regions: active and inert respectively.

[7] The increase of respiration found to result from the presence of light, is probably an _indirect_ effect. It is most likely due to the reception of more vivid impressions through the eyes, and to the consequent nervous stimulation. Bright light is associated in our experience with many of our greatest outdoor pleasures, and its presence partially arouses the consciousness of them, with the concomitant raised vital functions.

[8] To exclude confusion it may be well here to say that the word "atom" is, as before explained, used as the name for a unit of a substance at present undecomposed; while the word "molecule" is used as the name for a unit of a substance known to be compound.

[9] On now returning to the subject after many years, I meet with some evidence recently assigned, in a paper read before the Royal Society by Mr. J. W. Pickering, D.Sc. (detailing results harmonizing with those obtained by Prof. Grimaux), showing clearly how important an agent in vital actions is this production of isomeric changes by slight changes of conditions. Certain artificially produced substances, simulating proteids in other of their characters and reactions, were found to simulate them in coagulability by trifling disturbances. "In the presence of a _trace of neutral salt_ they coagulate on heating at temperatures very similar to proteid solutions." And it is shown that by one of these factitious organic colloids a like effect is produced in coagulating the blood, to that "produced by the intravenous injection of a nucleoproteid."

[10] After this long interval during which other subjects have occupied me, I now find that the current view is similar to the view above set forth, in so far that a small molecular disturbance is supposed suddenly to initiate a great one, producing a change compared to an explosion. But while, of two proposed interpretations, one is that the fuse is nitrogenous and the charge a carbo-hydrate, the other is that both are nitrogenous. The relative probabilities of these alternative views will be considered in a subsequent chapter.

[11] When writing this passage I omitted to observe the verification yielded of the conclusion contained in § 15 concerning the part played in the vital processes by the nitrogenous compounds. For these vegeto-alkalies, minute quantities of which produce such great effects in exalting the functions (_e. g._, a sixteenth of a grain of strychnia is a dose), are all nitrogenous bodies, and, by implication, relatively unstable bodies. The small amounts of molecular change which take place in these small quantities of the vegeto-alkalies when diffused through the system, initiate larger amounts of molecular change in the nitrogenous elements of the tissues.

But the evidence furnished a generation ago by these vegeto-alkalies has been greatly reinforced by far more striking evidence furnished by other nitrogenous compounds--the various explosives. These, at the same time that they produce by their sudden decompositions violent effects outside the organism, also produce violent effects inside it: a hundredth of a grain of nitro-glycerine being a sufficient dose. Investigations made by Dr. J. B. Bradbury, and described by him in the Bradshaw Lecture on "Some New Vaso-Dilators" (see _The Lancet_, Nov. 16, 1895), details the effects of kindred bodies--methyl-nitrate, glycol-dinitrate, erythrol-tetranitrate. The first two, in common with nitro-glycerine, are stable only when cool and in the dark--sunlight or warmth decomposes them, and they explode by rapid heating or percussion. The fact which concerns us here is that the least stable--glycol-dinitrate--has the most powerful and rapid physiological effect, which is proportionately transient. In one minute the blood-pressure is reduced by one-fourth and in four minutes by nearly two-thirds: an effect which is dissipated in a quarter of an hour. So that this excessively unstable compound, decomposing in the body in a very short time, produces within that short time a vast amount of molecular change: acting, as it seems, not through the nervous system, but directly on the blood-vessels.

[12] This interpretation is said to be disproved by the fact that the carbo-hydrate contained in muscle amounts to only about 1.5 of the total solids. I do not see how this statement is to be reconciled with the statement cited three pages back from Professor Michael Foster, that the deposits of glycogen contained in the liver and in the muscles may be compared to the deposits in a central bank and branch banks.

[13] Before leaving the topic let me remark that the doctrine of metabolism is at present in its inchoate stage, and that the prevailing conclusions should be held tentatively. As showing this need an anomalous fact may be named. It was long held that gelatine is of small value as food, and though it is now recognized as valuable because serving the same purposes as fats and carbo-hydrates, it is still held to be valueless for structural purposes (save for some inactive tissue); and this estimate agrees with the fact that it is a relatively stable nitrogenous compound, and therefore unfit for those functions performed by unstable nitrogenous compounds in the muscular and other tissues. But if this is true, it seems a necessary implication that such substances as hair, wool, feathers, and all dermal growths chemically akin to gelatine, and even more stable, ought to be equally innutritive or more innutritive. In that case, however, what are we to say of the larva of the clothes-moth, which subsists exclusively on one or other of these substances, and out of it forms all those unstable nitrogenous compounds needful for carrying on its life and developing its tissues? Or again, how are we to understand the nutrition of the book-worm, which, in the time-stained leaves through which it burrows, finds no proteid save that contained in the dried-up size, which is a form of gelatine; or, once more, in what form is the requisite amount of nitrogenous substance obtained by the coleopterous larva which eats holes in wood a century old?

[14] This chapter and the following two chapters originally appeared in