CHAPTER V.

WEISMANNISM UP TO DATE (1893).

HITHERTO we have been considering Professor Weismann’s system as it stood prior to the publication of his most recent works on _Amphimixis_ and _The Germ-plasm_, in 1891 and 1893 respectively. These later and highly elaborate essays present considerable modifications of the system, as it stood when the foregoing criticism was written. But, for reasons already stated in the Preface, it appears to me desirable to leave that criticism as it was originally constructed, and to supply this further chapter for the purpose of dealing with the large alterations of, and important additions to, the theory of germ-plasm, which the maturer thought of its gifted author has led him to announce.

A few general remarks may be most conveniently made at the outset.

In the first place, these recent publications present the advantage over their predecessors of being systematic treatises, instead of more or less independent papers. On this account they present a logical sequence of thought, which renders the task of examination much less difficult than it was in the case of the first volume of the _Essays_.

In the second place, as a result of his more matured reflection, Professor Weismann has himself perceived a considerable number of the difficulties and objections which I have set forth in the preceding chapters. And not only has he thus anticipated many of my criticisms; but, as a result of doing so, he has changed not a few of the most important parts of his previous system, with the result of greatly improving it.

But, in the third place, notwithstanding that his remarkable power of speculative thinking is everywhere united with adequate knowledge in the sundry branches of biological science with which it deals, I confess to a serious doubt whether it has not been permitted to enjoy an undue amount of liberty. If only they can be laced together by a thread of logical connexion, hypotheses are added to hypotheses in such profusion as we are acquainted with in the works of metaphysicians, but which has rarely been approached in those of naturalists. The whole mechanism of heredity has been now planned out in such minuteness of detail and assurance of accuracy, that in reading the account one is reminded of that which is given by Dante of the topography of Inferno. For not only is the “sphere” of germ-plasm now composed of nine circles (molecules, biophores, determinants, ids, idants, idio-plasm, somatic-idioplasm, morpho-plasm, apical-plasm), but in most of these regions our guide is able to show us such strange and interesting phenomena, that we return to the fields of science with a sense of having been indeed in some other world. Or, to change the metaphor, if it be the case that “a true scientific judgement consists in giving a free rein to speculation with one hand, while holding ready the break of verification with the other,” I think it must be admitted that, in as far as he has erred, Professor Weismann has done so by driving a chariot which is unprovided with any break at all.

Hence, fourthly, it is needless to follow, even in epitome, the innumerable windings of these never-ending speculations. For, on the one hand, it would be impossible to do so without adding an unduly extended chapter to our already tediously prolonged consideration of Weismann’s views; while, on the other hand, we should have to deal merely with matters of comparative detail. The additions which have been made to his theory by his most recent publications are chiefly concerned with the matter just alluded to—viz., a minute elaboration of the hypothetical mechanism of heredity, in accordance with the general theory of germ-plasm. Without question this elaboration is everywhere thoughtful, and often highly ingenious; but until the general theory in question shall have been satisfactorily grounded, it seems premature to supply so immense a design of purely deductive construction. Beautiful though it may be in its imposing elevation, this drawing of “the architecture of germ-plasm” must be regarded as a work of artistic imagination rather than as one of scientific generalization. From the latter point of view it is at most a temple _in posse_, and even if it is ever to be realized _in esse_, we cannot allow the actual building to begin until we are much more sure than anybody is at present entitled to be touching the foundations on which it is proposed to rear so great an edifice.

Again, and fifthly, even if Weismann should ever be able to satisfy us upon this matter, or fully to demonstrate his basal proposition touching the perpetual continuity of germ-plasm, there would still be a far cry between accepting this sufficiently simple proposition and supposing that there is any adequate reason for entertaining so complex a scheme of the structure of germ-plasm. No doubt Weismann himself would be quite ready to admit, that from his basal proposition of the continuity of germ-plasm it is logically possible to construct many other designs of the architecture of germ-plasm, besides the one which he has so beautifully drawn. And although most of such alternative designs would doubtless embody some one or other of the features which are presented by his own, no one could say which features common to any two of the designs represent the facts. For in the case of all alike there would be a necessary absence of verification: the architects would all and equally have to acknowledge that their imposing pictures of “the palace of truth” were but imaginary. Such, in my opinion, has been the case with all theories of the ultimate mechanism of heredity hitherto published; but the difference between them and Weismann’s theory in this respect is, that while most of the others have not gone into speculative details further than was necessary as a means of substantiating their basal postulates, Weismann’s, as now developed in _The Germ-plasm_, is mainly concerned with such speculative details as an end, or object, _per se_.

But, it may be replied, by thus constructing an ideal mechanism of heredity Weismann is greatly strengthening his fundamental postulate of the continuity of germ-plasm, because he shows how all the main facts of heredity, and allied phenomena, admit of being explained if once the postulate be accepted. If this were urged, however, I should have two remarks to offer. The first is that Weismann, in constructing his ideal mechanism, has gone very much further in the way of elaboration than can possibly be required for this purpose. So much further, indeed, that his purpose has evidently been the constructing of his ideal mechanism, as I have just said, for its own sake, and not for the sake of substantiating its basal proposition by showing how well the latter can be made to work in explaining the phenomena of heredity, &c. Moreover—and this is my second remark—however well the basal proposition may be made to work in this respect, we must not be deceived into supposing that such a fact is equivalent to a substantiation of the proposition. This proposition—the continuity of germ-plasm—is the inverse of that which constitutes the basis of the theory of pangenesis. For while the latter assumes that in the last resort it is always somatic tissues which produce the substance of heredity, the former simply inverts the terms of this assumption, and holds that it is always the substance of heredity which produces the somatic tissues. Now, in all cases where one theory consists in thus simply inverting the terms of another, it will be found that the facts which they both seek to explain lend themselves equally to explanation by either, up to some certain and usually distant point, where a crucial test becomes possible. Take, as an example, the geocentric and heliocentric theories of the solar system. Here the question was whether the earth moved round the sun, or _vice versa_; and so many of the facts of observation lent themselves equally well to either interpretation, that it was very many centuries before the crucial tests were forthcoming. So, in the present instance, the question is as to whether the carriers of heredity move from body-cells to germ-cells, or _vice versa_; and it is because the theory which sustains the latter view has merely to invert the terms of the one which takes the former, that so many of the facts of observation lend themselves equally well to both—as we have seen in chapter III (pp. 56-59).

Lastly, yet another reason for not considering in any detail Professor Weismann’s intricate speculations on the ultimate mechanism of heredity is, that by so doing I should have found it impossible to avoid obscuring the main issues. For even Professor Weismann himself, by the extreme care which he has taken in fully presenting his scheme of this ultimate mechanism, has not found it practicable to keep distinctly before our view the relative insignificance of such details, as compared with the fundamental importance of his original postulates. Hence, I have deemed it best in the present chapter to restrict our attention to the changes which he has recently made in these the foundations of his entire system.

For these reasons, then, I will mention only those main features in the “architecture of germ-plasm” which it is necessary to understand for the purposes of the following criticism touching the general theory of germ-plasm in the most recent phase of its evolution.

* * * * *

To begin with, Weismann has now seen the desirability of ceasing to designate the ultimate “carriers of heredity” by the term “molecules.” Indeed, in these later volumes he has fully anticipated my remarks touching the use of this term in his previous “Essays[33].” The result of his more mature reflection may be presented in epitome thus.

A number of “molecules,” in the proper or chemical sense of the word, go to form a “biophore,” which is the ultimate unit of living substance.

A number of “ biophores” go to form a “determinant,” which is a special element in the germ-plasm, capable of directing the ontogeny of such and such a group of cells as is independently variable from the germ onwards.

A number of “determinants” go to form an “id,” which is the same hypothetical body as Weismann has hitherto designated by the term “ancestral germ-plasm.” That is to say, it is a group of determinants indissolubly united in phylogeny, and therefore transmitted by heredity as one complex whole. Ids are, perhaps, microscopically visible; and, if so, they probably correspond to the small granules (microsomata), which are familiar to the histologist in the structure of chromosomes.

A number of “ids” go to form an “idant,” which is a chromosome, or chromatin fibre[34].

In my opinion the most important advance which Weismann has made in his theory by means of this scheme has reference to the third of these divisions—the determinant. It is a matter of observation that every cell of a multicellular organism does not vary independently: it appears to be always the case that in the phenomena of variation a smaller or a larger _group_ of cells is concerned. Now there must be something that determines the similar and simultaneous variation of such a whole group of cells; and, in all cases where such a variation is congenital, it is certain that this something must be contained in the substance of heredity. So far, I think, we must all agree, whether or not we regard this substance as “germ-plasm.” In other words, whether we regard the carriers of heredity as proceeding centrifugally (germ-plasm) or centripetally (gemmules), it seems to me that we ought to accept Weismann’s doctrine of determinants. Indeed, pathologists have already furnished a foreshadowing of such a doctrine in regard to the phenomena presented by certain diseases, such as cancer; but it is an important step to have extended the idea from pathology to biology in general—and, at the same time, to have given it a more definite shape than it has hitherto presented. In Weismann’s hands it serves to render more conceivable—if not also more intelligible—that process of marshalling cell-formations, which, be our theories what they may, is assuredly the most distinctive and remarkable fact of ontogenetic organization.

Again, as regards the id, I do not see how any one can attentively read Professor Weismann’s discussion without acknowledging that, if we once accept his doctrine of determinants, his sequent doctrine of ids becomes a logical necessity.

On the other hand, however, I do not see that such is the case with respect to idants; and still less do I see any reason for identifying the latter with chromosomes—even assuming that chromosomes are the visible repositories of the carriers of heredity[35].

Referring the reader to Weismann’s own exposition for a full account of these and many other additions to his general theory of germ-plasm, I will at once proceed to consider the alterations or emendations of that theory which have been published in his last two volumes, and which, as we shall find, have in large measure anticipated some of the most important points in the foregoing criticism. Therefore in the following criticism I will consider _seriatim_ what he has now said touching all these points, and conclude by offering some general remarks on the resulting position of his general system of theories up to the present date.

Pursuing the same method of criticism as that adopted in the preceding chapters, we will first consider the further modifications of Weismann’s theory of heredity, and next those of his theory of organic evolution.

_Weismann’s theory of Heredity_ (1893).

First of all, Weismann has now profoundly modified his theory of polar bodies. For, owing to certain more recent researches of Professor O. Hertwig, he very candidly allows:—“My previous interpretation of the first polar body as the removal of ovogenetic nucleo-plasm from the egg must fall to the ground: about this there is no possible doubt[36].”

He now regards both polar bodies as concerned in the same function of removing superfluous germ-plasm. Therefore one-half of his previous theory is abandoned: “the ovogenetic idio-plasm” is now supposed to be simply absorbed in the course of ontogeny, as I had suggested in one of the preceding chapters (pp. 42-46). The consequence is that he has now nothing to oppose to the view which is likewise there suggested (pp. 43-44)—viz., that his whole theory of polar bodies is rendered needless and improbable by the fact that the very mode in which ova are produced renders ample provision for the removal of any amount of superfluous germ-plasm which the theory of germ-plasm may require.

It is needless to say, after what has already been said in the pages just referred to, that in my opinion Professor Weismann has improved his main system of theories by dropping this part of his subordinate and, for the most part, separate theory of polar bodies. I only wish he could have seen his way to dropping the whole.

* * * * *

Again, he has now fully considered the phenomena of repair, regeneration, reproduction from somatic tissues, budding, and graft-hybridization.

Touching the four former he takes the view which I have supposed that he would (p. 53). As regards the latter, he fully accepts the fact of an occasional transmission of characters from one species or variety of plant to another by mere grafting[37]. But, although the explanation which he gives of this fact may pass muster so far as the only case which he deals with in detail is concerned, I do not see how it can do so to many others. For the case which he considers is that of _Cystisus adami_, where a bud of one species of Laburnum having been inserted in the wood of another produced a shoot which presented intermediate characters; and these have ever since been propagated by cuttings. Weismann’s interpretation of the facts here is, “that they were due to an abnormal kind of amphimixis, so that the idants of both species were combined in the apical cell of the first shoot[38].” Now, although this explanation may well apply to a case of graft-hybridization by means of buds, it obviously cannot do so to any case where hybridization is produced by the grafting of woody tissues. For here there is no “apical cell” in the question; and therefore the difficulties which I have adduced on page 82 remain. Possibly Weismann may dispute the fact of hybridization in any of these cases; but, as he has not expressly done so, I will not go into the question of evidence[39].

* * * * *

One important addition to this side of Weismann’s system has been made in order to meet the class of difficulties which are presented by the apparent inheritance of certain climatic variations, as already mentioned on pp. 67-8. For example, his own butterflies seemed to render definite proof of somatogenetic variations caused by changed conditions of life being transmitted to progeny. Therefore, it will be remembered, Weismann candidly admitted, “even now I cannot explain the facts otherwise than by supposing a passive acquisition of characters produced by the direct influence of climate”—i.e., an exactly _representative_ copying in progeny of characters acquired by parents. I have already quoted these words in order to show their logical inadmissibility as used by Weismann. He cannot be allowed thus to entertain the Lamarckian factors and at the same time to maintain his theory of germ-plasm, which excludes them as physiologically impossible. Doubtless he was himself aware of this, for he immediately added that “new experiments will be necessary to afford the _true_ explanation[40].”

The explanation, however, which he now gives is not based on any new experiments, but on a new suggestion to the effect that all such seemingly conclusive instances of the inheritance of acquired characters are, in truth, illusory. This suggestion is that “Many climatic variations may be due wholly or in part to the simultaneous variation of corresponding determinants in some parts of the soma, and in the germ-plasm of the reproductive cells.[41]” For example, if, as Weismann now supposes, determinants of the same kinds occur in the somatic tissues as well as in the germ-cells, when a particular spot occurs on a butterfly’s wing, it has been due to a particular kind of determinant which in the course of ontogeny was transmitted from the germ-cell for the express purpose of controlling the size and colour of the spot. But a residue of precisely similar determinants was reserved in the germ-cell (germ-plasm), for the purpose of determining a precisely similar spot in the next generation. Hence, if a rise of temperature, or any other external change, is capable of so acting on the determinant in the soma as to cause it to impart an abnormal colour to the spot when formed, a similar change is likely to be simultaneously effected in the corresponding determinants which are lying dormant in the germ-plasm. Therefore, when the latter become active in the ontogeny of the next generation, they will produce spots presenting the same variations as those of the preceding generation. Obviously, however, there would not be here any transmission of acquired characters. The change would be “specialized,” but not “representative.”

No doubt we have here a sufficiently ingenious method of circumventing an awkward class of facts. But I should like to make two observations with regard to it.

In the first place, the suggestion is highly speculative, and has been advanced solely for the sake of saving the theory of germ-plasm. There are no facts adduced in its favour, and it could scarcely be entertained as in the least degree probable by any one who has not already accepted the theory in question. Hence, unless we are to embark on a course of circular reasoning, we must refuse to accept the explanation of hereditary climatic variation now offered, until it shall have been fully corroborated by the experimental enquiry to which Weismann says he is now submitting it.

My second observation is, that the suggestion is not new; but appears to have been derived from Professor Weismann’s recent study of Mr. Galton’s _Theory of Heredity_. At all events, the suggestion is there presented with sufficient lucidity, thus:—

It is said that the structure of an animal changes when he is placed under changed conditions; that his offspring inherit some of his change; and that they vary still further on their own account, in the same direction, and so on through successive generations, until a notable change in the congenital characteristics of the race has been effected. Hence, it is concluded that a change in the personal structure has reacted on the sexual elements. For my part, I object to so general a conclusion, for the following reasons. It is universally admitted that the primary agents in the processes of growth, nutrition, and reproduction are the same, and that a true theory of heredity must so regard them. In other words, they are all due to the development of some germinal matter, variously located. Consequently, when similar germinal matter is everywhere affected by the same conditions, we should expect that it would be everywhere affected in the same way. The particular kind of germ whence the hair sprang, that was induced to throw out a new variety in the cells nearest to the surface of the body under certain changed conditions of climate and food, might be expected to throw out a similar variety in the sexual elements at the same time. The changes in the germs would everywhere be collateral, although the moments when any of the changed germs happened to receive their development might be different[42].

This allusion to Mr. Galton’s _Theory of Heredity_ leads me to consider what Professor Weismann has said with regard to it in this latest publication, where, for the first time, he has dealt with it. In my opinion he has done but scant justice to the views of his predecessor, and therefore I will occupy some considerable space in seeking to justify this opinion.

As already stated, from the time that Mr. Galton published his theory I have felt that in its main contention it presents a probably true solution of the main problem of heredity—viz., to account for the contrast between congenital and acquired characters in respect of transmissibility. And this solution, as likewise already stated, was substantially identical with that which Professor Weismann published in the next decade. Indeed, the only important difference between these two theories of heredity is, that while Weismann’s excludes on deductive grounds the physiological possibility of the inheritance of acquired characters, Galton’s more judiciously leaves to be determined, by subsequent enquiry of the inductive kind, the question whether acquired characters are ever transmitted in faint degrees, or whether they are never transmitted at all. In addition to this important difference, however, there are certain others which seem to me of very little consequence, inasmuch as they have reference to speculations on the ultimate mechanism of heredity, or the intimate morphology and physiology of the carriers of heredity—speculations which it would be absurd to suppose can be other than purely conjectural. Therefore in my previous criticism I did not allude to these subordinate points of difference, but stated merely, in general terms, that Galton’s view of the ultimate mechanism in question was such as to leave room for the possibility of the occasional transmission of acquired characters. And in this respect, it still seems to me, his theory has an advantage over that of Weismann. No doubt the latter is a much more elaborate and highly finished piece of work; but beauty of ideal construction is no guarantee of scientific truth—as we shall presently find exemplified in a striking manner with regard to Weismann’s theory of evolution. And if his theory of heredity, in its final shape, is a much more precise, detailed, and logically coherent structure than any which has ever been framed in this department of biological thought, there is all the more reason to scan critically the fundamental postulate on which it rests. Hence I cannot help feeling that it will be time enough to consider minor differences between the two theories when the physiological possibility of the occasional transmission of acquired characters, as entertained by Galton’s theory, shall have been ruled out as demonstrably opposed to fact.

Seeing, however, that Professor Weismann thinks otherwise, and appears to attach as much importance to differences concerning deductive _minutiae_ as he does to those concerning fundamental principles, I will here contrast the two theories somewhat more in detail than heretofore, and with special reference to what he has now himself said touching their relationship.

It will be remembered that the primary or fundamental difference just alluded to is, that while the theory of germ-plasm postulates an _absolute_ continuity, the theory of stirp postulates but a _partial_ continuity, of the substance of heredity. Hence, according to Weismann’s view, we must go back to the unicellular organisms for the origin of this substance in the multicellular; and we must regard use-inheritance as physiologically impossible. On the other hand, according to Galton’s view, there is no necessity for us to do either of these things. The origin of stirp is to be found in the somatic tissues of the multicellular organisms themselves. Nevertheless, this theory differs greatly from pangenesis, in that the former supposes the origin of hereditary substance to be mainly given in the _phylogeny_ of any group of multicellular organisms, while the latter supposes it to be given mainly in each _ontogeny_, Galton’s theory is, that in each ontogeny only a small part of the stirp derived from parents is consumed in making the new organism—the larger part being handed over in trust for passing on to the next generation, in the same way as Weismann supposes to be the case with germ-plasm. Darwin’s theory, on the other hand, does not entertain any such notion of “continuity” in the substance of heredity from germ-cell to germ-cell of parent and offspring; it supposes that in each successive generation the germ-cells are _wholly_ supplied with their germinal material from somatic-cells of each individual organism. Or, adopting our previous terminology, the three theories may be ranked thus.

The particulate elements of heredity all proceed centripetally from somatic-cells to germ-cells (gemmules): the inheritance of acquired characters is therefore habitual.

These particulate elements proceed for the most part, though not exclusively, from germ-cells to somatic-cells (stirp): the inheritance of acquired characters is therefore but occasional.

The elements in question proceed exclusively in the centrifugal direction last mentioned (germ-plasm): the inheritance of acquired characters is therefore impossible[43].

Such being the fundamental points of difference between these three theories of heredity, we have now to consider more particularly those which obtain between Galton’s and Weismann’s.

The general doctrine of gemmules (i. e. somatic-cell-germs) is accepted by Galton; but instead of supposing, as Darwin supposed, that these minute bodies freely circulate through all the body tissues, so that some of them are absorbed from all the somatic-cells by the germ-cells, and there constitute the entire mass of hereditary material out of which the offspring will afterwards be formed, Galton supposes that gemmules circulate with comparative difficulty, and that only comparatively few of them gain access to the germ-cells in each generation. Hence, characters acquired in the individual lifetime are much less heritable than those which are called congenital. For congenital characters are due to the “continuity” of stirp through numberless generations in the phylogeny of the organism; hence such characters are represented by a vastly greater number of equivalent hereditary elements. Weismann, on the other hand, rejects the doctrine of gemmules _in toto_.

Again, according to Galton’s view, “individual [congenital] variation depends upon two factors; the one is the variability of the germ[44] and of its progeny; the other is that of all kinds of external circumstances, in determining which out of many competing germs, of nearly equal suitability, shall be the one that becomes developed. The variability of germs under changed conditions, and that of their progeny, may be small, but it is indubitable; absolute uniformity being scarcely conceivable in the condition and growth, and, therefore, in the reproduction of any organism. The law of heredity goes no further than to say, that like _tends_ to produce like; the tendency may be very strong, but it cannot be absolute[45].”

Here, of course, there is a wide difference between stirp and germ-plasm. For while Galton does not entertain amphimixis among the “factors” of congenital variation, Weismann, as we are now well aware, has hitherto regarded it as the sole cause of such variation. Nevertheless, as we shall presently find, Weismann has now greatly modified his views upon this point, and does entertain, in _The Germ-plasm_, both the “factors” mentioned by Galton. Hence, the difference between the two theories in question with regard to this matter is not nearly so wide as it was prior to the publication of Weismann’s last work.

The next most important point of difference between the theories of stirp and germ-plasm has reference to the mechanism of ontogeny. According to Galton, this is simply a struggle between all the carriers of heredity composing the stirp of a fertilized ovum. It is not, however, a struggle for existence, but what may be called a struggle for development. In the fertilized ovum all the carriers of heredity are, to begin with, in a “latent” condition; but of this enormous multitude of “germs” or “gemmules,” only a very small proportional number are destined to become “patent”—i. e., developed into the tissue-cells composing the new organism. The vast majority of the gemmules, or those which fail to be thus developed, go to constitute the stirp of the new organism when this has been formed by the development of the comparatively few successful gemmules. Thus much understood, the following quotation will be fully intelligible.

My argument is this: Of the two groups of germs, the one consisting of those that succeed in becoming developed and in forming the bodily structure, and the other consisting of those that remain continually latent, the latent vastly preponderates in number. We should expect the latent germs to exercise a corresponding predominance in matters of heredity, unless it can be shown that, on the whole, the germ that is developed into a cell becomes thereby more fertile than if it had remained latent. But the evidence points the other way. It appears both that the period of fertility is shorter, and the fecundity even during that period is less in the germ that becomes developed into a cell, than they are in the germ that remains latent. Much less then would the entire bodily structure, which consists of a relatively small number of these comparatively sterile units, successfully compete in matters of heredity with the total effect of the much more numerous and more prolific units which are in a latent form[46].

Thus, Galton’s theory of the mechanism of geny is a theory of struggle; and this constitutes a point of difference on which Weismann lays much stress in his latest work. For, as we know, Weismann regards the mechanism of ontogeny as characterized by a peaceful succession of “stages,” which are “pre-determined from the germ onwards”; and in his latest work this idea of orderly sequence has been further elaborated in his doctrine of “determinants.” In short, to adopt their own metaphors, while Galton tells us that the mechanism of ontogeny is like that of a political election, where rival candidates compete to “represent” the nation (stirp) in Parliament (individual organism); Weismann likens it to the mechanism of a well-drilled army, where ultimate carriers of heredity (privates) are banded together in companies, regiments, battalions, &c., under the command of corresponding officers (determinants).

Lastly, there is yet one further point of difference between stirp and germ-plasm, which is thus stated by Weismann:—

Galton’s idea is only conceivable on the presupposition of the occurrence of sexual reproduction, while the theory of the continuity of the germ-plasm is entirely independent of any assumption as to whether each primary constituent is present in the germ _singly_ or in numbers. According to my idea, the active and the reserve germ-plasm contain precisely similar primary constituents, gemmules, or determinants; and on this the resemblance of a child to its parent depends. The theory of the continuity of the germ-plasm, as I understand it, is not based on the fact that each “gemmule” necessary for the construction of the soma is present many times only, so that a residue remains from which the germ-cells of the next generation may be formed: it is founded on the view of the existence of a special adaptation, which is inevitable in the case of multicellular organisms, and which consists in the germ-plasm of the fertilized egg-cell becoming doubled primarily, one of the resulting portions being reserved for the formation of germ-cells[47].

These being the main points of difference between the theories of stirp and of germ-plasm to which Professor Weismann has alluded, I will now proceed to consider them separately, in reverse order to that in which they have been here stated.

The point of difference last mentioned need not detain us long, because it seems to me one of very little importance. “Whether each primary constituent is present in the germ singly or in numbers” cannot greatly signify, so long as both theories agree that, sooner or later, they must be present plurally. Galton supposes them to be thus present from the first (i. e. in the unfertilized ovum), while Weismann supposes them to be so only as a result of their self-multiplication at a somewhat later stage (i. e. in the segmenting ovum, and onwards throughout the procreative life of the individual). Doubtless Weismann does not suppose that they ever become so numerous as Galton imagines; but the whole question is so highly speculative that I do not see how any useful purpose can be served by debating it. Nor do I see why Weismann should conclude that “Galton’s idea is only conceivable on the presupposition of the occurrence of sexual reproduction.” It is true that Galton has discussed exclusively the case of sexual reproduction; but I cannot perceive that any of his ideas are inapplicable to a-sexual.

Touching the question whether the phenomena of ontogeny had best be ascribed to a competition among a vast number of “germs,” or to a strictly ordered evolution of a comparatively small number of “determinants,” a considerable array of arguments might be adduced in support of either view. Thus, Galton might well maintain that his interpretation of the observable facts is most in accordance with the general analogies supplied by organic nature as a whole. The ancient aphorism of Heraclitus, “Struggle is the father, king, and lord of all things,” has been in large measure justified by Darwin and his followers, at any rate within the range of biology. Not only have we the “struggle for existence” where “the origin of species” is concerned; but Roux has well argued, in his remarkable work on _Der Kampf der Theile im Organismus_, that the principle of “struggle” is concerned to an equally important extent as between all the constituent parts of the same individual. But if this is so—if every tissue-cell of the organism owes its maintenance to success in a general contest for nutriment, &c.,—do we not find at least a probability that it owes its origin as a visible cell to a similar success in a similarly general contest among the invisible elements from which tissue-cells are developed? Nay, does it not seem well nigh incredible that when this selection-principle is seen to be the governing cause of evolution everywhere else, it should cease to play any part at all just at the place where we are unable to see what is going on? As we are agreed that this “father of all things” is of prime importance in phylogeny—to say nothing of physiology, psychology, and sociology,—must we not deem it absurd to suppose that it is supplanted in ontogeny by the opposite principle of absolute peace?

On the other hand, Weismann adduces many forcible considerations _per contra_; so that, in the result, I deem it best to dispose of the question with two general remarks. The first is, that the rival views are not necessarily incompatible. Each may present one aspect of the truth. Weismann’s doctrine of determinants may be—and, to the best of my judgement, must be—sound; but this does not hinder that Galton’s doctrine of struggling “germs” may be so likewise. For, as we have already seen, these germs present the same compound character which belong to determinants; in fact I do not suppose that Galton would object to identifying them with determinants. On the other hand, I do not see why Weismann should object to supposing that similar determinants compete among themselves for ontogenetic development. Indeed, he has already argued, in his suggestive theory of “germ-tracts,” that it is usually only one among a number of similar determinants which does succeed in achieving such development—or, as he expresses it, which “becomes active.” But what is it that causes this activity? Surely it must be some superiority on the part of the active determinant over its passive companions. And, if so, it is the selection-principle that is here at work. In fact, he has himself laid no small stress on what he calls “the struggle of the determinants of the two parents in ontogeny,” and has even supplied a long section on “the Struggle of the Ids in Ontogeny.” Therefore I do not see why he should so emphatically dissent from Galton’s view upon this matter as he does in his work on _The Germ-plasm_[48].

My second remark is a brief one—viz., that the whole question is of so very speculative a character, that I cannot see the smallest use in debating it.

The only remaining point of difference between strip and germ-plasm is the one referring to stability. Needless to say, Galton is at one with Weismann in recognizing a high degree of stability on the part of the substance of heredity; but the agreement extends only so far as is necessitated by the facts of atavism, &c. Indeed, he does not even mention—although he perhaps implies—what Weismann has called amphimixis as among the factors of individual congenital variation. Weismann, on the other hand, has hitherto regarded amphimixis as the sole cause of all such variations. But, as we shall presently find, in his recent work on _The Germ-plasm_ he has now greatly modified his views upon this subject, and, in fully recognizing the “factors” of variability to which Galton alludes, has correspondingly lessened the difference between germ-plasm and stirp. But this is a point which can be better dealt with when we come to consider the important modifications which in this respect the theory of germ-plasm has undergone.

* * * * *

The only other matter which has to be mentioned in connexion with Weismann’s theory of heredity is, that in _The Germ-plasm_ he has for the first time given us his views upon the influence of a previous sire on the progeny of a subsequent one by the same dam. The phenomena in question, which I have already detailed in pp. 77-9, 110, he designates by the term “telegony.” The analogous phenomena in plants he calls, following Focke, “xenia.”

With regard to telegony, he adopts, almost precisely, the position which I surmised that he would. That is to say, he first disputes the alleged facts, and then argues that, even if they be facts, they admit of being explained on the theory of germ-plasm by supposing that some of the germ-plasm from the first sire penetrates the unripe ova which are afterwards fertilized by the second[49]. The only difference between his views and my own upon this matter is, therefore, as follows.

Supposing that the phenomena alleged ever occur in fact, I have said that the only way of explaining them would seem to be, “that the life of ‘germ-plasm’ is not conterminous with that of the spermatozoa which convey it, and hence that, if the carriers of heredity, after the disintegration of their containing spermatozoa, should ever penetrate an unripe ovum, the germ-plasm thus introduced might remain dormant in the ovum until the latter becomes mature, and is then fertilized by another sire. In this way it is conceivable that the hitherto dormant germ-plasm of the previous sire might exercise some influence on the ontogeny of the embryo[50].”

Now, this is substantially the position which Weismann takes up: only instead of supposing that it is the “carriers of heredity” of the first sire which gain access to the unripe ovum “after the disintegration of their containing spermatozoa,” he supposes that it is one of the spermatozoa which does so before its disintegration has commenced. Of course there is here no difference in principle, but only a question touching the mode in which the access is presumably effected. But, as regards this question, I retain my original opinion. For, while I can see no theoretical difficulty in supposing that “the carriers of heredity,” when set free by the disintegration of their containing spermatozoa, may reach the unripe ova while still embedded in the depths of the ovary, I do see a difficulty, amounting almost to a physiological impossibility, in supposing that a whole spermatozoon can perform such a feat. From all that we know about the powers and functions of spermatozoa in the vertebrata, it appears simply absurd to imagine that these bodies are able to penetrate the dense coating of an ovary, and then delve their way through the stroma. There is, indeed, a remarkable investigation which was published a year or two ago by Mr. Whitman[51] which appears to prove that in certain leeches the male injects his seminal fluid into any part of the body of the female, and that the spermatozoa then reach the ova by wandering about her general tissues until some of them happen to hit upon her ovary. But in this case the spermatozoa are specially adapted to perform such acts of penetration—being spear-like bodies provided with a sharp point. Hence, if Weismann should quote this instance, it would not tend to support his view, seeing that the spermatozoa of mammals do not exhibit any such specializations of structure; and therefore, before any one of them can effect fertilization, must wait for the ovum to mature, reach the surface of the ovary, and rupture its follicle.

But, as already observed, it does not signify, so far as we are here concerned with the matter, in what precise manner the telegonous influence may be supposed to be exercised—provided that it may be so _directly_, and not necessarily through first having to influence the whole material organism. Therefore I quite agree with Weismann that the facts—supposing them to be facts—are quite as explicable by the theory of germ-plasm as by that of pangenesis[52].

Again, with respect to xenia, Weismann writes:—

As such eminent botanists as Focke, and more recently De Vries, have expressed much doubt with regard to these observations—or rather interpretations—we must wait until these cases have been critically re-investigated before attempting to account for them theoretically. The chief difficulty we should meet with in any such explanation would be due to the fact that we are here concerned with the influence of the _germ-plasm_ of the sperm-cell on a tissue of another plant which only constitutes _a part_ of this plant. It would thus be necessary to assume that all the determinants of this germ-plasm are not active, and that only those take effect which determine the nature of the fruit.

Now, it does not appear that De Vries has looked into the matter on his own account, as he merely refers to what Focke has said. And this amounts merely to showing the dubious character of some half-dozen cases which Focke gives as those which alone have fallen within his cognizance. Why he does not mention any of the numerous cases which are quoted by Darwin, I do not understand. Nor can I understand why he does not consider what seem to be the particularly conclusive facts given on p. 80,—i. e., where xenia appears to constitute “a needful preliminary to fertilization.” But the whole matter is one for botanists to deal with, and if any doubt attaches to it, at least the grounds of such doubt should be fully stated. Still more, in my opinion, should the matter be freed from any such doubt. The question—if there be a question—is one of great interest from a merely physiological point of view, while in relation to the fundamental problems of heredity its importance is immense. Surely, then, any competent botanist who disputes the facts ought to test them by way of experiment.

But, be this as it may, I must call prominent attention to the following very remarkable words wherewith Weismann concludes the passage above quoted. For he there says, that even supposing there were no doubt as to the facts or their interpretation, “the chief difficulty” which they would oppose to the theory of germ-plasm would be, “that we are here concerned with the influence of the _germ-plasm_ of the sperm-cell on a tissue of another plant which only constitutes _a part_ of this plant.” In other words, Weismann now freely entertains the possibility of a direct action of germ-plasm on the somatic tissues, even though these belong to another individual! Thus he now concedes the only point for the establishment of which I adduced the phenomena of xenia, in Chapter III: the whole of one side of that “reciprocal action between the sphere of germinal-substance and the sphere of body-substance,” which I contended for on pp. 76-85, is now conceded; and although it is the less important side, its surrender goes far to weaken the doctrine of a perpetual isolation of germinal-substance to a “sphere” of its own. If we suppose that the germinal substance of one organism may thus directly act upon the somatic tissues of another, and that changed conditions of life are able to produce simultaneously an acquired character in the soma and a precisely identical character as congenital in the germ (pp. 129-30), we are plainly inviting ourselves to abandon the complex explanation of living material in “two kinds,” where one is capable in all sorts of ways of communicating with the other, while the possibility of any reciprocal action is excluded. For the simpler hypothesis of living material as all of one kind encounters no such antinomies. So long as one kind of this material was supposed to be as distinct from the other as a parasite is distinct from its host, there was not so much to choose between the theory of germ-plasm and that of gemmules in this respect of simplicity. But the more that the former theory has had to be adjusted to facts, the greater has its complexity become, until now its own author is obliged to make so many additional assumptions for the purpose of mantaining it, that we begin to wonder how long it can continue to support the weight of its accumulating difficulties.

* * * * *

So much for the main modifications which have this year been made in Weismann’s postulate of the perpetual continuity of germ-plasm. We must next consider the changes which he has effected in his companion postulate of the absolute stability of germ-plasm.

_Weismann’s Theory of Evolution (1893)._

Of far more importance than any of the alterations which Professor Weismann has recently made in his theory of heredity, are those whereby he has modified his sequent theory of evolution. For while, as we have just seen, his work on _The Germ-plasm_ leaves the former theory substantially unaltered,—although largely added to in matters of detail,—it so profoundly modifies the latter that careful readers will find no small difficulty in ascertaining how much of it has been allowed to remain. I will consider only the main modifications, and these I will take separately.

* * * * *

It will be remembered that one distinctive feature in Weismann’s theory of evolution has hitherto been, that the unicellular organisms differ from the multicellular in the following important particulars.

1. There being no division in unicellular organisms between germ-cells and somatic-cells, there is no possibility in them of the occurrence of amphimixis.

2. Consequently, there is no possibility in them of congenital variations, in the sense that these occur in multicellular organisms.

3. Hence the only causes of individual variation and of the origin of species in the unicellular organisms are the Lamarckian factors, just as in the multicellular the only cause of these things is natural selection.

4. Hence, also, the unicellular organisms are potentially immortal, while the multicellular have acquired mortality for certain adaptive reasons.

But now, with the exception of No. 4, all these positions have been abandoned. For, chiefly on account of the beautiful researches of Maupas, Weismann has come to perceive that no real distinction can be drawn between an act of sexual union in the multicellular organisms, and an act of conjugation in the unicellular. Amphimixis, therefore, is now held by him to occur equally in both these divisions of organic nature, with the consequence that the Protozoa and Protophyta owe their individual variations, and therefore the origin of their innumerable species, as exclusively to the action of natural selection as is the case with the Metazoa and Metaphyta. In fact, the term “amphimixis” has been coined in express relation to these very points.

It will be seen, however, that this important change of view merely postpones the question as to the origin of amphimixis, if the object of this process be that which Weismann supposes—viz., the providing of material in the way of congenital variations on which natural selection can act. Therefore he is obliged to assume that there now are, or once have been, organisms of a less organized character than even the lowest of the unicellular forms—organisms, that is to say, which possess no nucleus, but are wholly composed of undifferentiated bioplasm. These most primitive organisms it must have been that were not subject to any process of natural selection, but, in virtue of an exclusive action of the Lamarckian factors upon their protoplasmic substance, gave rise to individual variations which subsequently gave rise to a unicellular progeny—when the process of natural selection was immediately inaugurated, and thereafter entirely superseded the Lamarckian factors. Or, to state the matter in Weismann’s own words:—

My earlier views on unicellular organisms as the source of individual differences, in the sense that each change called forth in them by external influences, or by use and disuse, was supposed to be hereditary, must therefore be dismissed to some stage less distant from the origin of life. I now believe that such reactions under external influences can only obtain in the lowest organisms which are without any distinction between nucleus and cell-body. All variations which have arisen in them, by the operation of any causes whatever, must be inherited, and their hereditary individual variability is due to the direct influence of the external world.... If I am correct in my view of the meaning of conjugation as a method of amphimixis, we must believe that all unicellular organisms possess it, and that it will be found in numerous low organisms, in which it has not yet been observed[53].

It is not very clear, at first sight, how Professor Weismann, after having thus abandoned the propositions 1, 2, and 3, as above stated, manages to retain his former view as given in No. 4. Nevertheless he does so, by representing that a unicellular organism, even though it present such a considerable degree of organization as we meet with in the higher Protozoa, still resembles a germ-cell of a multicellular organism, in that it consists of all the essential constituents of a germ-cell, including germ-plasm in its nucleus. And inasmuch as a germ-cell is potentially immortal, so it must be with a unicellular organism; in the one case, as in the other, the design of the structure is that its contained germ-plasm shall fuse with the germ-plasm contained in the nucleus of another individual cell, when the life of both will be preserved. For my own part, however, I cannot see that in either case the _cell_, as distinguished from its contained _germ-plasm_, is thus shown to be potentially immortal. On the contrary, it appears to me a mere accident of the case that in a unicellular organism the immortal substance (germ-plasm) is contained in a single cell, which is at the same time a _free_ cell, and, as such, is denominated an “organism.” We might just as well call a germ-cell an “organism,” whether as an ovum it happens to be embedded in a mass of somatic-cells, or as a locomotive spermatozoon it happens to be free. In fact Weismann himself appears to recognize this. But, if so, it is surely a distinction without a difference to say that unicellular organisms are immortal, while multicellular are mortal. For in neither case is the organism immortal, while in both cases it is the germ-plasm (i.e., the substance of heredity) that is so. Where the cell containing the germ-plasm happens to be a free cell, it is called an “organism”; but whether it be a germ-cell or a protozoan, it alike ceases to be a cell when it has given origin to a multitude of other cells, whether these happen to be other germ-cells (_plus_ somatic-cells) or other protozoan cells. In short, _quâ_ cell, all cells are mortal: it is only the substance of heredity which some cells contain that can be said, in any sense of the term, to be immortal. For the immortality in question does not belong to unicellular organisms as such, but to the germ-plasm which they contain. And from this it follows that, as the immortality of germ-plasm is one and the same thing as the continuity of germ-plasm, by alleging an immortality as belonging to the unicellular organisms, Weismann is merely restating his fundamental postulate. Hence, also, he is but denying, in a somewhat round-about way, the occurrence of spontaneous generation.

I conclude, therefore, that his sole remaining distinction between the unicellular and the multicellular organisms is but illusory, or unreal. And, with regard to the great change which he has thus effected in his system by expressly abolishing all the other distinctions, I have only to say that in my opinion he has thereby greatly improved his system. For he has thus relieved it of all the formidable difficulties which he had needlessly created for himself, and which I have already enumerated in the foregoing pages (88-89). In his ever-shifting drama of evolution the unicellular organisms have left the stage _en masse_, and, so far as they are concerned, we are all as we were before the curtain rose.

* * * * *

But of even more importance than this fundamental change of view with regard to the unicellular organisms, is a further and no less fundamental change with regard to the multicellular. That such is the case will immediately become apparent by a simple statement of the fact, that Weismann has now expressly surrendered his postulate of the absolute stability of germ-plasm!

We have already seen that, even in the first volume of his _Essays_, there were some passages which gave an uncertain sound with regard to this matter. But as they seemed attributable to mere carelessness on the part of their author, after quoting a sample of them, I showed it was necessary to ignore such inconsistent utterances—necessary, that is, for the purpose of examining the theory of germ-plasm as even so much as a logically coherent system of ideas[54]. For we have seen that if any doubt were to be entertained touching the _absolute_ stability of germ-plasm “since the first origin of sexual propagation,” a corresponding measure of doubt would be cast on Weismann’s theory of congenital variation as _solely_ due to amphimixis, with the result that his whole theory of evolution would be similarly rendered dubious. Since then, however, he has gone very much further in this direction. First, in reply to Professor Vines he says (1890):—

I am at present inclined to believe that Professor Vines is correct in questioning whether sexual reproduction is the only factor which maintains Metazoa and Metaphyta in a state of variability. I could have pointed out in the English edition of my “Essays” that my views on this point had altered since their publication; my friend Professor de Bary, too early lost to science, had already called my attention to those parthenogenetic Fungi which Professor Vines justly cites against my views; but I desired, on grounds already mentioned, to undertake no alteration in the essays[55].

Next, in his essay on _Amphimixis_ (1892), there are several passages to somewhat the same effect; while, lastly, in his _Germ-plasm_ (1893), the fundamental postulate in question is, as I have said, expressly surrendered. For example, we have in the following words the final conclusions of his recent arguments. Speaking of amphimixis, he says:—

_It is not the primary cause of hereditary variation._ By its means those specific variations which already exist in a species may continually be blended in a fresh manner, but it is incapable of giving rise to new variations, even though it often appears to do so.... _The cause of hereditary variation must lie deeper than this. It must be due to the direct effects of external influences on the biophores and determinants._[56]

These quotations are enough to show that Weismann has now abandoned his original theory of congenital variations being exclusively due to amphimixis, and adopts in its stead the precisely opposite view—viz., that the origin of all such variations must be ascribed to the direct influence of causes acting on germ-plasm from without. Up to the present year the very essence of the whole Weismannian theory of evolution has been that, owing to the stability of germ-plasm since the first origin of sexual propagation, “the origin of hereditary individual variations cannot indeed be found in the higher organisms, the Metazoa and Metaphyta; but is to be sought for in the lowest—the unicellular organisms,” because “the formation of new species, which among the lower Protozoa could be achieved without amphigony, could only be attained by means of this process in the Metazoa and Metaphyta. It was only in this way that hereditary individual differences could arise and persist[57].”

But about the beginning of the present year we have this fundamental doctrine directly contradicted in such words as:—

_The origin of a variation_ is equally independent of selection and amphimixis, and is due to the constant occurrence of slight inequalities of nutrition in the germ-plasm[58].

This complete reversal of his previous doctrine brings Weismann into line with Darwin, who long ago gave very good reasons for the following conclusion:—

Those authors who, like Pallas, attribute all variability to the crossing either of distinct races, or to distinct individuals belonging to the same race but somewhat different from each other, are in error; as are those authors who attribute all variability to the mere act of sexual union [_amphimixis_][59].

And again:—

These several considerations alone render it probable that variability of every kind is directly or indirectly caused by changed conditions of life. Or, to put it under another point of view, if it were possible to expose all the individuals of a species during many generations to absolutely uniform conditions of life, there would be no variability[60].

Hence, Darwin was disposed to find the main, if not the only, causes of congenital variations in circumstances depending for their efficacy on the _instability_ of what Weismann calls germ-plasm. And the noteworthy fact is, that Weismann has now adopted this view, to the destruction of his originally fundamental postulate touching the _stability_ of germ-plasm since the first origin of sexual propagation.

* * * * *

By such a right-about-face man[oe]uvre, Weismann has placed his critics in a somewhat difficult position. For, in the first place, it is only towards the close of _The Germ-plasm_ that the man[oe]uvre is executed, and then only in a few sentences such as I have just quoted—italicized, it is true, but otherwise so slightly emphasized that, as Professor Hartog has observed, no one of his reviewers has noticed it[61]. In the second place, he nowhere expressly recognizes the effects upon his theory of evolution, which necessarily follow from the change. And, lastly, the manner in which he endeavours to underpin that theory after having thus removed its logical foundation in his former postulate of the absolute stability of germ-plasm, is so peculiar that it is hard to epitomize his reasoning with due regard to brevity.

Speaking for myself, I can only say that my first impulse, after reading the sentences above quoted, was to cancel the whole of Chapter IV, as well as all those parts of Chapters I and III where the Weismannian theory of evolution is alluded to; and then to start anew with a bare statement that this theory had now been wholly discarded by its author. But after due consideration it seemed desirable to leave the criticism as it was originally written, not only on account of the reasons already stated in the Preface, but still more because I found it would be impracticable to start a new criticism of the greatly modified theory of evolution without introducing many and lengthy parts of the old one, for the purpose of showing how the most recent theory had been arrived at. Hence, seeing that my previous criticism was far from having been rendered obsolete by the large changes which had taken place in Weismann’s system of theories, I concluded that it was best to retain what I had written, and add the present paragraphs for the purpose of dealing exclusively with the changes in question.

In now proceeding to do this, I think it is needless to occupy space by giving the reasons which have caused Weismann thus to abandon his doctrine of the universal stability of germ-plasm since the first origin of sexual propagation, and to substitute the precisely opposite doctrine of its universal instability. It is enough to say that these reasons all arise by way of logical necessity from the further working out in _The Germ-plasm_ of his theory of heredity—or, more correctly, from the additions which he has there made to his previous views on the mechanism of heredity. Thus he has reversed his former doctrine touching the absolute stability of germ-plasm, not so much on account of any of the general considerations or particular facts which I have adduced against it in Chapter IV, as because it would not tally with the recent additions which he has made to other parts of his system. Any one who cares to follow this matter will find the reasons in question fully and lucidly stated in Chapter XIV of _The Germ-plasm_[62].

It is of more importance to consider the means whereby Weismann seeks to save his theory of evolution after he has thus removed its foundation in his former postulate of the absolute stability of germ-plasm. As far as I can understand, he seeks to do so as follows.

In the first place, it must be noted that after his changes of view with regard to polar bodies, unicellular organisms, and the significance of sexual reproduction, nothing remains of his original theory of evolution save what he can manage to retain of his original theory of variation as due to amphimixis. But, as we have just seen, he has surrendered this latter theory also. Therefore, at first sight it appears that no part of the former can possibly remain. Beginning at the apex, he has removed, stone by stone, his doctrine of descent, and, on arriving at its fundamental postulate—the absolute stability of germ-plasm—simply turns it upside down. Surely, therefore, it may be thought, there is here as complete a destruction as well could be of all this side of Weismann’s system. Such, however, he endeavours to show is not the case. He regards it as still possible to retain so much of his theory of descent as is presented by what he can save of his theory of variation, thus:—

Although he now represents that the _instability_ of germ-plasm is such that in _no_ case can amphimixis have had anything to do with the _origin_ of congenital variations, he continues to regard the _stability_ of germ-plasm sufficiently great to necessitate, in _all_ cases, the occurrence of amphimixis in order to promote the _development_ of congenital variations. In other words, notwithstanding that he now thinks all congenital variations must be begun by external conditions acting directly on an unstable germ-plasm, he also thinks that the _amount_ of variation thus produced is likely to be exceedingly minute, and must therefore be increased by subsequent amphimixis in order to fall within the range of natural selection. So that, although powerless to initiate congenital variation, amphimixis must still play an indispensable part in the process of evolution, as in all cases a necessary condition to the occurrence of natural selection. External conditions first cause slight changes in the determinants of a species; but these are so slight that they have to be augmented by amphimixis before they constitute material on which natural selection can act, and hence before they can become of any significance either in ontogeny or phylogeny.

Such, I take it, is what Professor Weismann would now have us to understand; for otherwise I should have expected from him as frank a surrender of his theory of evolution (or the remnant thereof in his theory of variation) as he has made of its fundamental postulate. But, if such is his meaning, I may mention the reasons which appear to me to render it nugatory.

In the first place, it is evident that in thus minimizing the possible range of congenital variation due to the action of external conditions on a non-absolutely stable substance of heredity, Weismann is making a wholly gratuitous assumption, for the sole purpose of saving what remains of his theory of evolution—i. e., the doctrine of the immense importance of amphimixis.

We have already seen in the foregoing chapter that his original assumption of the _absolute_ stability of germ-plasm was a gratuitous one, made for the purpose of supplying a foundation for constructing his theory of evolution. But still more gratuitous is the assumption which he has now substituted, for the purpose of saving as much of this theory as is left—the assumption, namely, that germ-plasm, although universally unstable, nevertheless everywhere presents only a certain low degree of instability, which serves to accommodate his modified theory of heredity on the one hand, and all that is possible of his previous theory of evolution on the other. His original assumption, untenable though it was, furnished at least a logical basis for the necessary conclusion that amphimixis was the only possible cause of congenital variations. But there is not so much as any logical sequence in the now substituted assumption, that (A) all congenital variations are ultimately due to the _universal instability_ of germ-plasm, and (B) that nevertheless they are all more proximately due to such _a high degree of stability_ of germ-plasm as necessitates amphimixis as the only means whereby variations can be made “perceptible.” These statements are as independent of one another as any two statements can well be; and, therefore, if the second of them is to be substantiated, it can only be so by some totally distinct line of reasoning. The first statement does not even tend to suggest the second; in fact it tends to suggest the precise contrary. For, obviously, there is nothing in the logic of the matter to show why, if all congenital variations depend for their origin on the instability of germ-plasm, such instability must nevertheless be always so slight that the variations due to it must afterwards depend on amphimixis for their development to the point where they become “perceptible.” As above indicated, it is surely little short of absurd thus to assume that a universally unstable germ-plasm universally presents only that particular degree of instability which will serve to accommodate Professor Weismann’s newer theory of heredity, and at the same time to save thus much of his previous theory of evolution.

But now, in the second place, not only is this assumption wholly gratuitous, but there are many considerations which render it in the highest degree improbable, while there are not wanting facts which appear to demonstrate that it is false. For, unquestionably, most of the considerations which have already been advanced in the preceding chapter against the assumption of an absolute stability of germ-plasm, are here equally available against the assumption of an imperceptibly small amount of instability[63]. Similarly, all the facts there given with regard to the a-sexual origin of species—and even genera—of parthenogenetic organisms, bud-variation[64], &c., amply demonstrate that congenital variations due to the instability of germ-plasm alone, or apart from amphimixis, are sometimes enormous. Hence, we cannot accept the gratuitous suggestion that in all other cases they are too insignificant to count for anything till they have been augmented by amphimixis, even although we may be prepared to agree that amphimixis is probably one important factor in the production of congenital variations. What degree of importance it presents in this connexion, however, we have not at present any means of determining; all we can conclude with certainty is, that in some cases it is demonstrably very much less than Weismann supposes, while it is extremely improbable that it is ever in any case the sole and necessary antecedent to the operation of natural selection.

This extreme improbability is shown, not only by what I have already said in the previous chapter, and need not here repeat; but likewise by the “several considerations” which Darwin has adduced with regard to this very point, and which, as he says, “alone render it probable that variability of every kind is directly or indirectly caused by changed conditions of life,” with the consequence that “those authors who attribute all variability to the mere act of sexual union are in error.” I have already quoted these words further back in the present chapter, in order to show that by now attributing the _origin_ of all congenital variations to the direct action of external conditions, Weismann has brought himself into line with Darwin so far as this fundamental point of doctrine is concerned. But I here re-quote the words in order to show that by further attributing the _development_ of congenital variations “to the mere act of sexual union,” Weismann is again falling out of line with Darwin. So to speak, he first performs a right-about-face movement as regards his original position towards the “stability of germ-plasm,” and immediately afterwards makes a half-turn back again. Now, it is this half-turn to which I object as unwarranted in logic and opposed to fact.

In a previous chapter (pp. 66-7) I presented to him the dilemma, that germ-plasm must be either absolutely stable or else but highly stable, and that in the former case his theory of amphimixis as the sole cause of congenital variations would be valid, while in the latter case the theory would collapse. But it did not then occur to me that Weismann might seek a narrow seat between the horns of this dilemma, by representing that germ-plasm is universally unstable up to a certain very low degree of instability—viz., exactly that degree which is required for starting a congenital variation by means of external causes, without its being possible for the variation to become perceptible unless afterwards increased by means of amphimixis. And now that this extremely sophistical position has been adopted, I cannot see any imaginable reason for adopting it other than a last endeavour to save as much as possible of his former theory of evolution. There can be nothing in the nature of things thus to limit, within the narrowest possible range, the instability of a universally unstable germ-plasm—distributed, as this most complex of known substances is, throughout all species of plants and animals, and exposed to inconceivably varied conditions of life in all quarters of the globe. And these considerations are surely of themselves enough to dispose of the assumption as absurd, without again rehearsing the facts of congenital variation which definitely prove it to be false.

_Conclusion._

For reasons stated at the commencement of this chapter, I have restricted its subject-matter almost exclusively to a consideration of the more fundamental changes which Professor Weismann has wrought in his general system of theories by the publication of his most recent works. In other words, I have purposely avoided considering those immensely elaborate additions to his theory of heredity which constitute by far the largest portion of his essays on _Amphimixis_ and _The Germ-plasm_, and which have for their object an ideal construction of “the architecture of germ-plasm.”

The fundamental changes to which allusion has just been made are as follows.

Professor Weismann has to a large extent abandoned his theory of polar bodies, and in my opinion would have done well had he taken a further step and surrendered the theory _in toto_.

Similarly, he has withdrawn his previous distinctions between the unicellular and multicellular organisms. The Protozoa and Protophyta are now included by him in the same category as the Metazoa and Metaphyta, as regards all matters of individual variation, reproduction, subjection to the law of natural selection, and so forth. The only difference which he continues to allege is the somewhat metaphysical one touching mortality and immortality. But I have given what appears to me sufficiently good reasons for ignoring this distinction; and therefore, as it seems to me, every one of Weismann’s previous doctrines respecting unicellular organisms have vanished—very much to the benefit of his system as a whole.

By far the greatest change, however, which he has made in this general system is that which he has effected by surrendering the postulate of the absolute stability of germ-plasm. The rift in his lute which has been noticed with regard to this matter has now been widened to an extent which _does_ prevent any further harping on the theme of evolution. It is true that Weismann endeavours to retain as far as possible the general character of his former postulate of the universal stability of germ-plasm, with the consequent “significance of sexual reproduction” as the sole cause of congenital variation. For although he now reverses both these doctrines by saying that germ-plasm is universally unstable, and that sexual reproduction is in no case the sole cause of congenital variation, he seeks at the same time to minimize the logical consequences of such reversal by making an ingenious assumption, the possibility of which I had not foreseen when writing the previous chapters. The assumption is, that although germ-plasm is universally unstable, the degree of its instability is everywhere restricted within the narrowest possible limits; so that sexual propagation is still necessary for the purpose of _developing_ congenital variations to the point where they can fall within the range of natural selection, notwithstanding that they must all have been _originated_ by external causes acting directly on a germ-plasm universally unstable within the narrow limits assumed. But clearly this assumption is arbitrary to the last degree, and, no less clearly, it is made by Weismann for the sole purpose of saving as much as he can of his previous theory of variation. His more recent speculations touching the mechanism of heredity are incompatible with his former view of amphimixis as the _sole_ cause of congenital variations, and therefore he makes this arbitrary assumption for the purpose of representing that amphimixis may nevertheless still be regarded as a _necessary con-cause_. I need not here repeat what has so recently been said touching the sophistry of this assumption in theory, or the demonstrable falsity of it in fact. It is enough to remark, in conclusion, that the game is not worth the candle. It was originally well worth Weismann’s while to sustain his fundamental postulate of the _absolute_ stability of germ-plasm, because he was able to rear upon it his whole theory of evolution. But the only part of this theory which he has now left standing, or which he can now save by his newer postulate of a germ-plasm both stable and unstable at the same time, is his doctrine of variation. So to speak, it is his desire to reserve as much as is speculatively possible from the general ruin of his theory of descent, that causes him to go so far to attempt so little. For I cannot suppose that he himself will expect any of his readers to entertain so arbitrary, fanciful, and demonstrably false an assumption as the one in question. Surely it would have been better to have surrendered _in toto_ this “Weismannian theory of variation,” rather than to have attempted its rescue by means so plainly nugatory. It might still have been held that amphimixis plays a large and important part as one of the causes of variation, and therefore also as one of the factors of organic evolution. After having reversed his postulate of amphimixis being the sole cause of variability, and therefore having agreed with Darwin that “those writers are in error who attribute all variability to the mere act of sexual union,” he might well have questioned Darwin’s further statement as to its being “probable that variability of every kind is directly or indirectly caused by changed conditions of life.” But by now assuming that variations due to any causes other than amphimixis must be “imperceptible” until they have been augmented by amphimixis, Weismann is shutting out, with a futile hypothesis, the important question as to whether, or how far, amphimixis really is a cause of variation. Observe, the case is not as it might have been were there no reasons assignable for the occurrence of sexual propagation, other than that of assisting in the production of congenital variations. The theory of “rejuvenescence,” for example, is _prima facie_ a more probable one than that which ascribes to sexual propagation the function of causing variability[65]; while Galton’s hypothesis, which supposes the object of this form of propagation to be that of conserving the “germs” (= “determinants”) of the phyla, has a good deal to say for itself[66]. Of course such alternative hypotheses touching “the significance of sexual reproduction” are not necessarily exclusive of one another: the process may subserve two or more adaptive purposes[67]. But he would be a bold man who, in the present state of our knowledge, could accept unreservedly the particular view of this process which Darwin so emphatically rejected; and I think he must be a biased man who could entertain for an instant the modification of this view which Weismann has now substituted.

Thus, the Weismannian theory of evolution has entirely fallen to pieces with the removal of its fundamental postulate—the absolute stability of germ-plasm. It only remains to mention once more the effects of this removal upon the other side of his system—viz., the companion postulate of the uninterrupted continuity of germ-plasm, with its superstructure in his theory of heredity.

Briefly, these effects are as follows:—

1. Germ-plasm ceases to be continuous in the sense of having borne a perpetual record of congenital variations from the first origin of sexual propagation.

2. On the contrary, as all such variations have been originated by the direct action of external conditions, the continuity of germ-plasm in this sense has been interrupted at the commencement of every inherited change during the phylogeny of all plants and animals, unicellular as well as multicellular.

3. But germ-plasm remains continuous in the restricted, though still highly important sense, of being the sole repository of hereditary characters of each successive generation, so that acquired characters can never have been transmitted to progeny “representatively,” even although they have frequently caused those “specialized” changes in the structure of germ-plasm which, as we have seen, must certainly have been of considerable importance in the history of organic evolution.

4. By surrendering his doctrine of the _absolute_ stability of germ-plasm on the one hand, and of its _perpetual_[68] continuity on the other, Weismann has greatly improved his theory of heredity. For, whatever may be thought of his recent additions to this theory in the way of elaborate speculation touching the ultimate mechanism of heredity, it is a great gain to have freed his fundamental postulate of the continuity of germ-plasm from the two further postulates which have just been mentioned, and the sole purpose of which was to provide a basis for his untenable theory of evolution.

5. In my opinion it only remains for him to withdraw the last remnant of his theory of evolution by cancelling his modified and even less tenable views on amphimixis, in order to give us a theory of heredity which is at once logically intact and biologically probable.

6. The theory of germ-plasm would then resemble that of stirp in all points of fundamental importance, save that while the latter leaves the question open as to whether acquired characters are ever inherited in any degree, the former would dogmatically close it, chiefly on the grounds which I have considered in Appendix II. It seems to me that in the present state of our knowledge it is more prudent to follow Galton in suspending our judgement with regard to this question, until time shall have been allowed for answering it by the inductive methods of observation and experiment.

7. Hence, in conclusion, we have for the present only to repeat what Weismann himself has said in one of the wisest of his utterances,—“The question as to the inheritance of acquired characters remains, whether the theory of germ-plasm be accepted or rejected.”

It is now close upon twenty years that I accepted the substance of this theory under the name of stirp; and since that time the question as to the inheritance of acquired characters remains exactly where it was. No new facts, and no new considerations of much importance, have been forthcoming to assist us in answering it. Therefore, as already stated in the Preface, I intend to deal with this question hereafter as a question _per se_, or one which is not specially associated with the labours of Professor Weismann.

APPENDIX I:

ON GERM-PLASM.

AS already stated in the text (p. 71), Weismann’s general reasoning in support of his own theory of germ-plasm, as against Darwin’s theory of gemmules in any form, admits of being reduced to arguments in favour of three propositions—viz., first, that there is no evidence of the transmission of somatogenetic characters; secondly, that the theory of pangenesis, which seeks to explain their supposed transmission, is “inconceivable”; and, thirdly, that its logical antithesis—the theory of germ-plasm—is so much less beset with difficulties, that by comparison it is simple, self-coherent, and offers a real, as distinguished from a “formal,” explanation of the facts of heredity.

The first of these propositions will be discussed at considerable length in my next volume. The second and third propositions, however, may be dealt with here.

The following paragraph, which I shall quote sentence by sentence, sets forth the grounds on which Weismann bases the second proposition, namely, that any theory belonging to the order of pangenesis—i. e., which supposes the carriers of heredity ever to travel centripetally—is, from its very nature, inconceivable.

At first sight this hypothesis seems to be quite reasonable. It is not only conceivable that particles might proceed from the somatic to the reproductive cells, but the very nutrition of the latter at the expense of the former is a demonstration that such a passage actually takes place. But a closer examination reveals immense difficulties. In the first place, the molecules of the body devoured are never simply added to those of the feeding individual without undergoing any change, but, as far as we know, they are really assimilated, that is, converted into the molecules of the latter. We cannot therefore gain much by assuming that a number of molecules can pass from the growing somatic cells into the growing reproductive cells, and can be deposited unchanged in the latter, so that, at their next division, the molecules are separated to become the somatic cells of the following generation[69].

The obvious answer to this is, that no one has ever supposed “gemmules” to be merely “_molecules_,” in the chemical sense of this word; nor has any one ever imagined that they are “_devoured_” by the germ-cells into which they pass. Of course, if this were the case—i.e., if gemmules serve merely as _food_ to the germ-cells—they would become disintegrated down even to their chemically molecular structure, and there would be an end of them as organized “carriers of heredity.”

In the second place, it is asked:—

How can such a process [i.e. the passage of gemmules into growing germ-cells] be conceivable, when the colony becomes more complex, when the number of somatic cells becomes so large that they surround the reproductive cells with many layers, and when at the same time, by an increasing division of labour, a great number of different tissues and cells are produced, all of which must originate _de novo_ from a single reproductive cell?

Here, again, the obvious answer is, that no one has ever propounded such a statement. Far from supposing that “all the different cells and tissues of a complex organism must originate _de novo_ from a _single_ reproductive cell,” the theory of pangenesis supposes the very contrary—viz., that somatic changes in the past history of the phyla have _not_ thus originated in _any_ reproductive cell. The idea of somatic changes originating in reproductive cells belongs to the theory of _germ-plasm_; but even this theory does not suppose all the great number of different cells and tissues which compose a complex organism to have ever originated _de novo_ from a _single_ reproductive cell.

The difficulty touching germ-cells becoming isolated, or buried, by the phylogenetic increase of somatic cells, is enforced in the immediately succeeding sentences, thus:—

Each of these various elements [somatic cells] must, _ex hypothesi_, give up certain molecules to the reproductive cells; hence those which are in immediate contact with the latter would obviously possess an advantage over those which are more remote. If, then, any somatic cell must send the same number of molecules to each reproductive cell[70], we are compelled to suspend all known physical and physiological conceptions, and must make the entirely gratuitous assumption of an affinity on the part of the molecules for the reproductive cells. Even if we admit the existence of this affinity, its origin and means of control remain perfectly unintelligible if we suppose that it has arisen from differentiation of the complete colony. An unknown controlling force must be added to this mysterious arrangement, in order to marshal the molecules which enter the reproductive cell in such a manner that their arrangement corresponds with the order in which they must emerge as cells at a later period.

Now I do not see much force in the suggestion that those somatic cells which happen to be in immediate contact with germ-cells, “must obviously possess an advantage over those which are more remote.” On the contrary, I do not see that mere proximity of one species of cell to another species within the same organism need have anything to do with the matter—still less that “we must suspend all physical and physiological conceptions,” if we demur to the statement that it “obviously must.” As for “physical conceptions,” how many thousands of cases might not be pointed to among chemical and mechanical processes where contact or proximity are conditions of comparatively little importance? And as for “physiological conceptions,” do we find that any part of the organism is affected by its distance, say, from the liver and kidneys, for getting rid of its effete products? Is it not rather the case that every gland in the body is wholly unaffected by its distance from any part of the body, in regard to its function of draining off the particular substances with which it is concerned? Why then should the reproductive gland constitute a conspicuous exception? Or how do we suspend all physiological conceptions, if we suppose that this gland resembles every other gland in being specialized to _secrete_ a particular kind of “molecule,” which, because thus specially _selected_, may be said to have for that gland a special “affinity”? If there are such things as gemmules, I do not see any violation of physiological analogies—still less an “entirely gratuitous assumption”—in supposing that they can be filtered out from all parts of the body by the sexual glands, and there aggregated as a special product to be discharged in the form of sexual elements[71].

But, it is further represented, “even if we admit the existence of this affinity, an unknown controlling force must be added to this mysterious arrangement, in order to marshal the molecules which enter the [growing] reproductive cell in such a manner that their arrangement corresponds with the order in which they emerge as cells at a later period.” Surely, however, for Weismann of all naturalists it ought not to be difficult to find this “unknown controlling force.” For of all naturalists he is perhaps the most ready to invoke the agency of natural selection as sufficient to explain every case—actual or imaginable—of _adaptation_. Now, here is a case where natural selection, one would think, is positively bound to act—supposing that there be such things as gemmules. For, if “the carriers of heredity” are gemmules, it is evident that their mutual “affinities” must be adaptively “marshalled” at each step of phylogenetic evolution, before any further advance of such evolution can be possible. And I do not see anything more “inconceivable” in supposing the establishment of such mutual affinities step by step through natural selection, than in supposing any other course of adaptive development by similar means. For, as Darwin has well shown, while anticipating this particular objection to his theory,—“The assumed elective affinity of each gemmule for that particular cell which precedes it in due order of development is supported by many analogies.” The analogies which he then gives are so numerous that I must here refer to his own discussion of the subject[72]—a discussion which is entirely ignored by Weismann.

Lastly, the principal ground, as far as I can see, which Weismann has for regarding Darwin’s theory in any shape “inconceivable,” is his own supposition that there is as complete an anatomical separation between the soma and its germ-cells as there is, for example, between the mammalian soma and these same cells when afterwards detached from the ovary and developing as foetuses _in utero_. In other words, the only connexion is supposed to be that of deriving nourishment by way of imbibition. But, as regards the germ-cell while still forming in the ovary or testicle, there is for this supposition no basis in fact. There is nothing in the histology of spermatogenesis that lends countenance to the supposition, while in the case of the ovum such histological evidence as we possess makes altogether against it. As Professor Vines has remarked:—

It cannot be seriously maintained that the whole body of the embryo is developed solely from the germ-plasm of the ovum. On the contrary, since the embryo is developed from the whole of the nucleus and more or less of the cytoplasm of the ovum, it must be admitted that the non-germ-plasm of the ovum provides a large part of the material in embryogeny. It is an obvious inference that, under these circumstances, hereditary characters may be transmitted from the parent to the offspring, not only by the germ-plasm, but also by the somato-plasm, of the ovum[73].

Again, and apart from this consideration, it is now known that a very intimate network of protoplasmic fibres connects the cell-contents of cellular tissues, both in plants and animals. So that here we have another very possible means of communication between the germ-cells and the somatic-cells which together constitute a multicellular organism.

Therefore, in so far as histology can be trusted to constitute a basis for generalizations of this kind at all, it does not sustain the supposition that there can be no medium of communication between the general cellular tissues of an organism and its specially reproductive elements. On the contrary, the microscope is able to demonstrate possible roads of connexion—and this even upon Weismann’s own view as to a specialized germinal substance which is restricted to the nucleus of an ovum. In short, the supposition as to an absolute anatomical separation between germ-plasm and somato-plasm is a deduction from Weismann’s theory itself: it is not supported—it is discredited—by histological observation. Hence, it cannot be accepted as valid evidence in favour of the theory from which alone it is derived, or as a valid objection to the rival theory of pangenesis.

Once more, even if it were true that histology proves an absolute anatomical isolation on the part of germ-cells, it would still have remained unquestionable that there is no absolute _physiological_ isolation. For, at least, the germ-plasm derives its nourishment from the soma in which it resides; and who shall say that the process of mere imbibition is not amply sufficient to admit of the passage of “gemmules”? Call them what we choose, the “carriers of heredity” must be so unimaginably small, that in relation to histological cells they must be as gnats to camels. Yet we know that even camels in the form of “migrating cells” of various kinds are able to pass through living membranes; and we also know that the microbes of syphilis can penetrate both ova and spermatozoa. Why then should it be deemed inconceivable that, where all such things can pass, gemmules can do so likewise?

Lastly, I have recently spoken of the detached condition of a ripe ovum _in utero_. Now it seems to me more “inconceivable” that such an ovum should be capable of announcing, as it were, to the walls of the uterus whether or not it is in a fertilized condition, than it is that, before quitting the ovary, it should have had some kind of physiological converse with its environing soma. Yet it is certain that, without any visible medium of communication, the impregnated ovum is able to inform the uterus that it is impregnated; and thereupon the uterus behaves towards that ovum in an altogether astonishing manner, such as it never displays towards an unimpregnated ovum. Of course various hypotheses may now be formed to account for this fact, seeing that no one can question it as a fact. But supposing that the fact could be questioned, with how much greater effect might it be argued that any communication between the ovum and its soma is even more antecedently incredible when the ovum is entirely free than when it is still contained within its ovary.

Now these, as far as I can find, are the only grounds for Weismann’s repeated assertion that the theory of pangenesis in any form is “inconceivable.” I have therefore endeavoured to show that this is too strong a statement. All the facts and considerations whereby he seeks to support it were present to the mind of Darwin; and, quite apart from any question of relative authority, I cannot avoid agreeing with Darwin that, whether or not the theory is true, at all events the “difficulties” attaching to it on these merely _a priori_ grounds are not insuperable, or such as to render his “pet child” an unconceived monstrosity in logic, or a proved absurdity in science.

Be it understood, however, that I am not here defending the theory of pangenesis. I am investigating the theory of germ-plasm; and it is because Weismann seeks to sustain the latter by excluding the former as preposterous, that I have been obliged thus to consider the validity of his criticism. For the point to which I am leading is, that Weismann gains nothing in the way of support to his own theory by this disparagement of Darwin’s, _unless he can show that the former supplies some more “conceivable” explanation touching the mechanism of heredity_. Now I am unable to see that he has shown this. What I do see is that his _a priori_ argument from “inconceivability” cuts both ways, and that it makes at least as much against germ-plasm as it does against gemmules. Therefore, having now considered what Weismann has said against the conceivability of gemmules on grounds of general reasoning, I shall proceed to show that quite as much—or even more—may be said in the way of a _tu quoque_. In other words, we have now finished with the second of the three propositions which we are examining (see p. 71), and proceed to our consideration of the third.

First of all, I do not see any greater difficulty in supposing that the “carriers of heredity” proceed centripetally from somatic-cells to germ-cells, than in supposing that they proceed centrifugally from the germ-cells to the somatic-cells which they are engaged in constructing. Nor do I see any more difficulty in imagining these “carriers of heredity” to be capable of constructing a new organism if they have first proceeded centripetally, and are thus severally representative of all parts of the parent organism _after its construction has been completed_, than I do if they have proceeded centrifugally, and are thus similarly representative of all parts of that organism _before its construction has been commenced_[74].

Similarly, it seems to me, whatever cogency there may be in Weismann’s objection to Darwin’s theory on the score that it must assume “an unknown controlling force in order to marshal the molecules,” is equally great as regards his own. True, Weismann has a lot to say about the control which nucleo-plasm can exercise on cell-formation, and germ-plasm on marshalling successive stages of ontogeny; but all that this amounts to is a re-statement of the facts. Such a controlling force must be equally assumed by both theories; but in each alike there is an absence of any ghost of an explanation.

Again, whatever difficulty there may be in conceiving the transition of somatic substance, _mutatis mutandis_ there must be an equal difficulty in conceiving the transition of germinal substance into somatic substance. Indeed, as far as I can see, the difficulty is even greater in the latter case than it is in the former. For the very essence of Weismann’s view is that germ-plasm differs from all or any other “plasm” in origin or kind: germ-plasm, and germ-plasm alone, has been immortal, perpetually continuous, capable of indefinite self-multiplication, and so of differentiating itself into an endless number and variety of somatic tissues. But, according to Darwin’s view, there is not, and never has been, any such fundamental difference between the essential nature of somatic elements, and the essential nature of sexual elements. On the contrary, it is supposed that both formative and formed material are one in kind—that all the cellular tissues of a multicellular organism, like the single cell of a unicellular organism, are _per se_ endowed with the vital property of self-multiplication; and that whether this property finds its expression in normal growth, in abnormal increments of growth (such as tumours), in processes of repair, in the various forms of a-sexual reproduction, or in the more specialized form of sexual fertilization, there is everywhere an exhibition of one and the same capacity. Now, without going further than this contrast between the fundamental principles of the two theories, does it not become evident that the difficulty of conceiving a transition of A into A´ is at any rate no greater than that of conceiving a transition of A into B, where A is in both cases the formative substance, A´ this same substance in another stage of evolution (i.e., elaborated for the performance of some special function, but never so as to lose its original function A), while B is a substance which differs from A almost as much as a woven texture differs from the hands that weave it?

Once more, in all his arguments which are directed to prove the continuity of germ-plasm, Weismann nowhere seems to perceive the necessity of arguing the correlative hypothesis—viz., that of the discontinuity of somato-plasm. Yet, as Professor Vines has remarked, it is as incumbent on him to disprove any possible continuity on the part of somato-plasm, as it is to prove a perpetual continuity on the part of germ-plasm. And here I am disposed to go further than Professor Vines has gone; for it appears to me even _more_ incumbent on Weismann to argue a discontinuity on the part of somato-plasm, than it is on him to argue a continuity on the part of germ-plasm.

This must be immediately apparent if we remember that, unless the discontinuity of somato-plasm be assumed, the theory of the continuity of germ-plasm in telluric time (as distinguished from eternity) becomes identical in form with all those theories of heredity to the family of which pangenesis belongs. All these theories go upon the assumption that living material has been continuous in telluric time—i.e., always derived from pre-existing material of the same kind; but they embody the further assumption that _all_ living material _is_ material of the same kind—i.e., everywhere presents the same fundamental properties. Weismann’s theory on the other hand, while adopting the first assumption, rejects the second; and assumes in its stead that living material exists in “two kinds,” only one of which has been continuous, while the other is discontinuous—being, in fact, formed anew at each ontogeny. Therefore, to my mind, it seems more needful to argue the point wherein his theory differs from these other theories of heredity, than it is to argue the point wherein it agrees with them. We look to him for a proof of the discontinuity of somato-plasm much more than we do for a proof of the continuity of germ-plasm. Now the only proof that he has to give of the discontinuity of somato-plasm—or, in other words, that the self-multiplication of somatic cells cannot take place unless the nucleus of each contains a self-multiplying idio-plasm derived from the nucleus of a germ-cell—is the non-transmissibility of somatogenetic characters. Here, however, there is an obvious equivoque. For his only test of characters as somatogenetic and blastogenetic consists in observing whether or not they are inherited: if they are inherited, he says they are blastogenetic: if they are not inherited, he says they are somatogenetic. But this is manifestly circular reasoning, so long as the question in debate is as to the truth of his theory. What we require in proof of the distinguishing feature of that theory—i.e., the discontinuity of the hypothetical somato-plasm—is not merely the obvious fact that some characters are inherited while others are not, but independent proof that inherited and non-inherited characters correspond to a continuity of germ-plasm on the one hand, and a discontinuity of somato-plasm on the other. He shows us, indeed, what was well known before, that characters developed during the lifetime of the individual are seldom (if ever) inherited, while characters developed during the lifetime of the species are always inherited. Obviously, however, this fact is no proof of the assumed correlation just mentioned, because, as Darwin has clearly pointed out, it may very well be due to the much shorter time which has been allowed for what may be termed the impress of heredity. Therefore, supposing (with Darwin and others) that living material is all of one kind, and continuous, the fact on which Weismann relies admits of being explained without resorting to his more complex supposition of living material in two kinds, the one perpetually continuous, and the other interrupted at each ontogeny.

For these reasons it appears to me that, so far as the argument from “inconceivability” is concerned, it makes at least as much against the theory of germ-plasm as it does against the theory of pangenesis; and, therefore, that no argumentative advantage is gained from its use by Weismann. The truth probably is that, _whatever_ the mechanism of heredity may actually be, it is at once so minute and so complex that its action is “inconceivable,” or, more correctly, unimaginable. Be it again understood, therefore, that I am not arguing in favour of pangenesis. I am merely criticising what appears to me an unsound argument in favour of germ-plasm. All this general or merely _a priori_ reasoning with regard to inconceivability is, as I have attempted to show, as available on the one side as on the other, and so fails to yield any observable advantage to either.

* * * * *

In conclusion it must be noticed, that Weismann now appears to have himself perceived the grave difficulties which lie against his antithesis between a hypothetical “germ-plasm” and a hypothetical “somato-plasm,” notwithstanding that the former becomes converted into the latter at each ontogeny. At any rate, he allows that Vines’ criticism upon this head is sound. But he is strongly of the opinion that, by means of a later emendation of his theory as originally published, he has succeeded in obviating these difficulties _in toto_. For my own part, as already several times observed in the text, I cannot in the least perceive that such is the case; and therefore I will quote _in extenso_ what he has said in answer to Professor Vines. It will be seen that his newer emendation of the theory consists in substituting for his original “somato-plasm” two substances, which are called respectively “somatic idio-plasm” and “cytoplasm.” And it is by means of this substitution that he thinks he has, in some way or another, overcome the contradiction involved in the doctrine (and, as it still seems to me, the essential doctrine of his whole theory of heredity) that “germ-plasm” becomes converted into “somato-plasm” during the course of every ontogeny. The following, at any rate, is his latest utterance upon the subject:—

I believe that the objections which Professor Vines makes to my theory of the continuity of germ-plasma rest solely on an unintentional confusion of my ideas, as he compares the opinions expressed in the second essay with those of the later ones, with which they do not tally. I will endeavour to make this clear. In this second essay (1883) I contrasted the body (soma) with the germ-cells, and explained heredity by the hypothesis of a “Vererbungs-substanz” in the germ-cells (in fact the germ-plasma), which is transmitted without breach of continuity from one generation to the next. I was not then aware that this lay only in the nucleus of the ovum, and could therefore contrast the entire substance of the ovum with the substance of the body-cells, and term the latter “somato-plasm.” In Essay IV (1885) I had arrived, like Strasburger and O. Hertwig, at the conviction that the nuclear substance, the chromatin of the nuclear loops, was the carrier of heredity, and that the body of the cell was nutritive but not formative. Like the investigators just named, I transferred the conception of idio-plasm, which Nägeli had enunciated in essentially different terms, to the “Vererbungs-substanz” of the ovum-nucleus, and laid down that the nuclear chromatin was the idio-plasm not only of the ovum but of every cell, that it was the dominant cell-element which impressed its specific character upon the originally indifferent cell-mass. From then onwards, I no longer designated the cells of the body simply as “somato-plasm,” but distinguished, on the one hand, the idio-plasm or “Anlagen-plasma” of the nucleus from the cell-body or “Cytoplasma,” and, on the other, the idio-plasm of the ovum-nucleus from that of the somatic cell-nucleus; I also for the future applied “germ-plasm “to the nuclear idio-plasm of ovum and spermatozoon, and “somatic idio-plasm” to that of the body cells (e.g., p. 184). The embryogenesis rests, according to my idea, on alterations in the nuclear idio-plasm of the ovum, or “germ-plasm”; on p. 186, et seq., is pictured the way in which the nuclear idio-plasm is halved in the first cell-division, undergoing regular alterations of its substance in such a way that neither half contains all the hereditary tendencies, but the one daughter-nucleus has those of the ectoblast, the other those of the entoblast; the whole remaining embryogenesis rests on a continuation of this process of regular alterations of the idio-plasm. Each fresh cell-division sorts out tendencies which were mixed in the nucleus of the mother-cell, until the complete mass of embryonic cells is formed, each with a nuclear idio-plasm which stamps its specific histological character on the cell.

I really do not understand how Professor Vines can find such remarkable difficulties in this idea. The appearance of the sexual cells generally occurs late in the embryogeny; in order, then, to preserve the continuity of germ-plasm from one generation to the next, I propound the hypothesis that in segmentation it is not _all_ the germ-plasm (i. e., idio-plasm of the first ontogenetic grade) which is transformed into the second grade, but that a minute portion remains unaltered in one of the daughter-cells, mingled with its nuclear idio-plasm, but in an inactive state; and that it traverses in this manner a longer or shorter series of cells, till, reaching those cells on which it stamps the character of germinal cells, it at last assumes the active state. This hypothesis is not purely gratuitous, but is supported by observations, notably by the remarkable wanderings of the germinal cells of Hydroids from their original positions.

But let us neglect the probability of my hypothesis, and consider merely its logical accuracy. Professor Vines says:—“The fate of the germ-plasm of the fertilized ovum is, according to Professor Weismann, to be converted in part into the somato-plasm (!) of the embryo, and in part to be stored up in the germ-cells of the embryo. This being so, how are we to conceive that the germ-plasm of the ovum can impress upon the somato-plasm (!) of the developing embryo the hereditary character of which it (the germ-plasm) is the bearer? This function cannot be discharged by that portion of the germ-plasm of the ovum which has become converted into the somato-plasm (!) of the embryo, _for the simple reason that it has ceased to be germ-plasm_, and must therefore have lost the properties characteristic of that substance. Neither can it be discharged by that portion of the germ-plasm of the ovum which is aggregated in the germ-cells of the embryo, for under these circumstances it is withdrawn from all direct relation with the developing somatic-cells. The question remains without an answer.” I believe myself to have answered this above. I do not recognize the somato-plasm of Professor Vines; my germ-plasm, or idio-plasm of the first ontogenetic grade, is not modified into the somato-plasm of Professor Vines, but into idio-plasm of the second, third, fourth, hundredth, &c. grade, and every one impresses its character on the cell containing it.

It may be dullness, but I confess that this does not appear to me an “answer” to Professor Vines’ criticism. Even though “idio-plasm of the first ontogenetic grade” has to become “idio-plasm of the second, third, fourth, hundredth, &c. grade,” before in each of the grades concerned it can give origin to the somatic-cells which are distinctive of that grade, I cannot see that it makes any difference (in relation to Vines’ criticism) whether we speak of those cells as containing “somato-plasm,” or as containing “somatic idio-plasm” of such and such a grade, _plus_ “cytoplasm.” For whether we thus follow Weismann’s earlier terminology or his later, we are so far speaking about exactly the same thing, namely, the transformation of “germ-plasm” into all the constituent cells of the “soma.” The difficulty is, in Vines’ words above cited, “to conceive that the germ-plasm of the ovum can impress upon the somato-plasm of the developing embryo the hereditary characters of which it (the germ-plasm) is the bearer”; and Weismann says that this difficulty, which he acknowledges, can now be answered by substituting for his original statement that “germ-plasm” becomes changed into “somato-plasm,” the statement that it is “idio-plasm” _derived_ from “germ-plasm” which thus “impresses its character on the cell containing it.” But, “as a matter of logical accuracy,” there is surely here a distinction without a difference. For what is the difference between saying that germ-plasm “impresses” its character on the contents of _all_ somatic cells considered collectively under the term “somato-plasm,” and saying that every “ontogenetic grade” of germ-plasm “impresses” _its_ character on _each_ successive group of somatic cells considered severally under the term “idio-plasm” of such and such a grade? At best this newer terminology has reference merely to a superadded hypothesis touching the _mode_—or rather the _history_—of the transition in question: it does not affect the original and essential doctrine of the transition itself.

APPENDIX II:

ON TELEGONY.

A WIDELY different view, however, is taken by Mr. Herbert Spencer with regard to the theoretical interpretation of telegony. This, indeed, is precisely the opposite view to the one which is given in the text. For while I agree with Professor Weismann in holding that the facts of telegony (supposing them to be facts) are as compatible with the theory of germ-plasm as with that of gemmules, “physiological units,” or any other theory which postulates a centripetal flow of the carriers of heredity from somatic-cells to germ-cells, Mr. Spencer is of the opinion that these facts are destructive of any theory which postulates a continuity in the substance of heredity—i.e., a centrifugal flow of the carriers of heredity. And, unquestionably, Mr. Spencer’s view is the prevalent one. Therefore, seeing that his opinion is not only of weight _per se_, but is shared by the scientific world in general, I will here transcribe a somewhat lengthy discussion which I have recently held with him upon the subject.

In the _Contemporary Review_ for March, Mr. Spencer wrote as follows:—

We pass now to evidence not much known in 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 fore-hand, and the dark bars across the back part of the legs[75].

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 of 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 English and French breeds of sheep. The writer of the translated paper, M. Malingié-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 seventy-five 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 these 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 of 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 perceived among 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 the 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.

My reply to this appeared in the April issue of the _Contemporary Review_, as follows:—

_Influence on Progeny of a Previous Sire._

This is the last of the arguments which Mr. Spencer advances against the position of Professor Weismann. Alluding to the case of Lord Morton’s mare, he represents that the phenomenon which it serves so well to illustrate—viz., the influence of a previous sire on the progeny of another by the same dam—is hopelessly at variance with the theory of germ-plasm. I cannot quite gather the explanation which he would give of this phenomenon, further than that in some way or another it betokens an immediate influence of the hereditary material of the male on the body-tissues (“somatic cells”) of the female. And this is the view which is taken of the phenomenon by the Lamarckians in general. Yet, if we consider all that such an explanation involves, we shall find that it is a highly complex explanation, for it involves the following chain of hypotheses:—The first impregnation affects many, if not all, the somatic tissues of the mother by the germinal matter of the father; these tissues, in their turn, react on the maturing ova; this action and reaction is such that when one of the ova is afterwards fertilized by a different sire, the resulting offspring more or less resemble the preceding sire. Unfortunately, neither Weismann himself nor any of his followers, as far as I know, has hitherto published an opinion on the subject; but I imagine that his answer would be three-fold. First, he may question the fact. Secondly, even admitting the fact, he may say it is much more easy to explain it by supposing that the germ-plasm of the first sire has in some way or another become partly commingled with that of the immature ova, as well as with that of the mature one which it actually fertilizes; and, if so, it would naturally assert its influence on the progeny of a subsequent sire. Millions of spermatozoa must have been playing around the ovaries after the first copulation, and only one of them was needed to fertilize the mature ovum. It is not necessary to suppose that some of the others succeeded in penetrating any of the immature ova, while these were still embedded in the substance of their ovaries. It may be that the life of “ids” Is not commensurate with that of their containing spermatozoa. After the latter have perished and disintegrated, their ids may escape in thousands of millions, bathing in a dormant state the whole surfaces of both ovaries. And, if so, it is conceivable that when subsequent ova mature—i.e., come to the surface of their ovaries and rupture their follicles—these dormant ids adhere to their porous walls, through which they may pass. This may not seem a very probable explanation; but, at any rate, it is a less improbable one than that on which the Neo-Lamarckians would found an argument against the continuity of germ-plasm. For,—

Thirdly, is it not literally inconceivable that this Neo-Lamarckian explanation can be the true one? Can it be seriously contemplated that there is any such mechanism as the explanation must needs assume? If it is difficult to accept such a machinery as is supposed by the theory of pangenesis, whereby every cell in the body casts off “gemmules,” which are the carriers of heredity from their respective tissues to the germinal elements, what are we to say of such a machinery as the following:—A machinery which distributes through the body of a female gemmules from the disintegrated spermatozoa of her mate; which distributes them _selectively_, so that they shall all eventually lodge in those tissue-cells of the female which correspond, part for part, with the tissue-cells of the male from which they were originally derived; which then insures that when a gemmule has thus reached its appropriate cell in the female body, it will thereupon modify the pre-existing gemmules in that cell, so that when they are shed and go to form the germinal contents of future ova, they endow the latter with the hereditary qualities of the male in question?

Such, it seems to me, is a fair statement of the whole case up to date. But I think it may be apposite now to publish the main results of an inquiry on which I have been engaged for the last three years.

First as to the facts. The investigations have been pursued on three different lines: (1) I raised discussions on the subject in the principal breeders’ and fanciers’ journals of this country, and also of America. (2) I entered into private correspondence with contributors of the largest experience, and also with professional and amateur breeders, fanciers, &c., who addressed me directly on the subject. (3) I started experiments with the varieties which these inquiries indicated as most likely to yield positive results. At present nothing need be said with regard to these experiments, because they are not sufficiently matured. But it is desirable to state the general upshot of the correspondence.

The principal result is to show that the phenomenon is of much less frequent occurrence than is generally supposed. Indeed, it is so rare that I doubt whether it takes place in more than one or two per cent. of cases. I must add, however, that nearly all my professional correspondents would deem this an absurdly low estimate. Most of them are quite persuaded that it is of frequent occurrence, many of them regard it as a general rule, while some of them go so far as to make a point of always putting a mare, a bitch, &c. to a good pedigree male in her first season, so that her subsequent progenies may be benefited by his influence, even though they be engendered by inferior sires. But I am certain that these estimates must be largely discounted in view of merely accidental resemblances, and still more on account of the prevalent belief upon the subject, which, where unquestioningly entertained, prevents anything like a critical estimate being formed.

But that the phenomenon does occur in some small percentage of cases there can be no reasonable doubt—as a result, I mean, of analysing the hundreds of cases which have now been submitted to me, especially with regard to dogs. One thoroughly well observed case occurring among pedigree animals is worth any number of slipshod statements, when precedent belief, inefficient isolation, exaggeration of memory, and so forth, have to be allowed for. On the present occasion space does not admit of giving such special instances, so I must ask it to be taken for granted that my evidence is enough to prove the fact of a previous sire asserting his influence on a subsequent progeny, although this fact is one of comparatively rare occurrence. It may be added that I have failed to find any good evidence of its ever occurring at all in the case of man. For although I have met with an alleged instance of a white woman, who, after having borne children to a negro husband, had a second family to a white one, in which some negro characteristics appeared, I have not been able to meet with any corroboration of this instance. I have made inquiries among medical men in the Southern States of America, where in the days of slavery it was frequently the custom that young negresses should bear their first children to their masters, and their subsequent children to negro husbands; but it never seems to have been observed, according to my correspondents, that these subsequent children were other than pure negroes. Such, however, was not the same case as the one above mentioned, but a reciprocal case; and this may have made a difference. If any reader should happen to know of another instance where a negro was the first husband, I hope he will inform me as to the result.

It has hitherto puzzled me why the phenomenon in question, since it does certainly occur in some cases, should occur so rarely as the above inquiries prove. But I think that Mr. Spencer’s suggestion on this point is a valuable one, as it seems to present an excellent promise of solving the puzzle.

This suggestion, it will be remembered, is that when the first sire is of a relatively stable and also of a markedly different ancestral stock from the dam—e.g., of a different species, as in the case of Lord Morton’s mare—there will be most likelihood of his impressing his ancestral characters on the progeny of the second sire[76]. And, as he remarks, it would indeed be an extraordinary coincidence if both the well-authenticated cases given in the College of Surgeons Catalogue should have conformed to his explanation by mere accident. To which I may add that the supposition of such an accidental coincidence would seem to be virtually excluded by the recent occurrence of yet a _third_ case of exactly the same kind. This took place in the Zoological Gardens, where a wild ass of one species was the previous sire to a foal born of another species: the subsequent sire was of the same species as the mother, and his foal, born a few months ago, presented an unmistakable resemblance to the other species. A brief account of the particulars is given by Mr. Tegetmeier in the _Field_ for December 14, 1892.

So much, then, for the facts. As regards their interpretation, it certainly seems to me that the one which I have supposed to be given by Weismann is less difficult of acceptance than the one which is given by the Lamarckians, as we have seen above. But it also seems to me that the latter explanation is not the only one available under the Lamarckian hypothesis. For, even under this hypothesis, there is no need to assume that the influence of the first sire is exerted on all the somatic tissues of the mother, and that these again reflect this influence on the ovum which is afterwards fertilized by the second sire. A mechanism that could effect all this may well be deemed impossible. But a much simpler explanation can be furnished by the Neo-Lamarckians, on lines similar to those upon which I have supposed that Weismann’s explanation would run. For, on their common supposition that the substance of heredity is particulate, it matters not in the present connexion whether we suppose the particles to be ids or gemmules. Indeed, it is more in accordance with the hypothetical endowments of the latter than of the former, that they should be capable of penetrating the coats of an ovum, if they can survive the disintegration of their containing spermatozoön. Nevertheless, thus far it does not seem to me that any theory belonging to the family of pangenesis can gain any advantage over the theory of germ-plasm, by appealing to the fact of a previous sire sometimes affecting the progeny of a subsequent one. The case, however, is widely different if we turn from animals to plants, thus.

The advantage which any theory of gemmules seeks to gain over the theory of germ-plasm by an appeal to the fact in question, consists in supposing that the influence of the previous sire is exercised in the first instance on the somatic cells of the female. For this would prove that the germinal elements of the male are capable of communicating their hereditary qualities, not only by mixing with the germinal elements of the female (as in ordinary fertilization) but also by direct contact with the general tissues of the female. And this again would prove that the fundamental postulate of the theory of germ-plasm is erroneous—i.e., the postulate of the continuity of germ-plasm, or of its perpetual restriction to a “sphere” of its own. This, as all who are acquainted with the literature of the subject will at once perceive, would be a serious blow to the whole Weismannian system. But, as we have seen, the current Lamarckian interpretation of the fact in question involves the supposition of a physiological machinery so inconceivably complex that instead of serving to corroborate the theory of gemmules (or of physiological units) it would go to render that theory incredible[77].

If, however, we turn to plants, we find a considerable number of facts which unquestionably demonstrate the only point which this interpretation has been adduced to suggest. For these facts show that, in not a few cases, the germinal matter of pollen-grains is capable of asserting its influence beyond the ovules to the somatic tissues of the ovary, and even to the flower-stalk of the mother plant. Here, then, we have simple and conclusive evidence of the material of heredity exercising a direct influence on somatic tissues. How this well-known fact is to be met by the theory of germ-plasm is a question which does not seem to have thus far engaged the attention of Professor Weismann, or of any of his followers. For particulars touching this phenomenon, so highly important in its relation to the theory of germ-plasm, I cannot do better than refer to the eleventh chapter of Darwin’s work on the “Variation of Animals and Plants under Domestication.”

Again, in the _Contemporary Review_ for May, Mr. Spencer wrote:—

In the essay to which this is a postscript, conclusions were drawn from the remarkable case of the horse and 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 connexion 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 pine-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[78].

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.

These further evidences, to which Mr. Fookes has since added others, render the general conclusion incontestable. 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....

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 case 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 proof that the surface of a mammalian ovarium is not a sperm-atheca. The third difficulty 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 emphasises exists, and the alleged inconceivability disappears.

To this I responded, in the _Contemporary Review_ for June:—

With regard to the influence of a previous sire, I ventured in my article to show that, even supposing it to be a fact, the phenomena concerned would not constitute any valid evidence against Weismann’s theory of germ-plasm, and, of course, still less would “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,” with the result that the phenomena in question “are simply fatal to Weismann’s hypothesis.” For a much simpler and more probable explanation is to be found in supposing that the unused germ-plasm of the first sire may survive the disintegration of its containing spermatozoa in the Fallopian tubes of the female, and thus gain access to the hitherto unripe ova _directly_, instead of first having to affect the whole maternal organism, and then being _reflected_ from it to them. I showed, at some length, how immensely complex the mechanism of any such process would necessarily have to be; and for the purposes of exposition I employed the terminology of Darwin’s theory of Pangenesis. Mr. Spencer now says: “In response, I have to ask why he [I] 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 expecially, deliberately ignoring my own hypothesis of physiological units?” Now my answer to this is very simple. I do not hold a brief for Weismann. On the contrary, I am in large measure an opponent of his views; and my only object in publishing my previous article was to save the theory of use-inheritance from what seemed to me the weaker parts of Mr. Spencer’s advocacy, while thus all the more emphasizing my acceptance of its stronger parts. Therefore, the impression which he seems to have gained from my attempts at impartiality is entirely erroneous. Far from “deliberately ignoring” any of his arguments or hypotheses which seemed to me at all available on the side of use-inheritance, I everywhere endeavoured to make the most of them. And, as regards this particular instance, I expressly used the term “gemmules,” instead of “physiological units,” simply because I could not see that, as far as my “mountain of difficulties” was concerned, it could make one atom of difference which term I employed. It now appears, however, that, in Mr. Spencer’s opinion, there is some very great difference. For, while he allows that the “mountain of difficulties” which I have “piled up” against his interpretation of the alleged phenomena would be valid on the supposition that the ultimate carriers of heredity are “gemmules,” he denies that such is the case if we suppose these ultimate carriers to be “physiological units.” For this statement, however, he gives no justification; and, as I am unable to conceive wherein the difference lies, I sincerely hope that in any subsequent editions of his pamphlet Mr. Spencer will furnish the requisite explanation. Gladly substituting the words “physiological units” wherever I have used the word “gemmules,” I am genuinely anxious to ascertain how he would overcome the “mountain of difficulties” in question. For I do not regard the subject as one of mere dialectics. It is a subject of no small importance to the general issue, Weismann _versus_ Lamarck; and, therefore, if Mr. Spencer could show that the phenomena in question make exclusively in favour of the latter, as he alleges, he might profitably inform us in what way he supposes them to do so.

In conclusion, I would like to take this opportunity of explaining that my former article was written in Madeira, where I did not receive a copy of Weismann’s most recent work, entitled _The Germ-plasm_, until the _Contemporary Review_ for April was being printed off. Thus, I was not then aware that in this work Professor Weismann had fully anticipated several of Mr. Spencer’s criticisms—including this matter of the influence of a previous sire. Here he adopts exactly the position which in my article I surmised that he would; so that, to all who have read _The Germ-plasm_, it must have appeared that I was prophesying after the event. Hence the need of this explanation.

Lastly, in the same issue of the _Contemporary Review_, Mr. Spencer explained:—

Mr. Darwin’s hypothesis of Pangenesis implies not only that the reproductive cell must contain numerous kinds of gemmules derived from different organs, but that the numbers of these gemmules must bear to one another something like the proportions which the originating organs bear to one another in size. The conception involves many different _kinds_, whose numbers are in many different _proportions_, and I supposed the difficulty alleged was, that for the influence of a previous sire to be communicated from the growing f[oe]tus to the mother would imply not only the transfer of the various kinds of gemmules derived from him, but also maintenance of their numerical proportions, and that again these gemmules, diffused throughout the maternal system, would have to be transferred in these proportions to the subsequently formed ova. No such difficulties arise if the units conveying hereditary characters are of one kind only.

From this it is apparent that Mr. Spencer has misunderstood “the difficulty alleged,” and that the desired explanation is not yet forthcoming. I did not say anything about “kinds” or “proportions” of the carriers of heredity; my difficulty is to conceive of any mechanism whereby these carriers can first directly influence the somatic-cells of the mother, and then indirectly reflect this influence upon her germ-cells. Also, I cannot see any obvious necessity for the intervention of the “embryo” in the process.

GLOSSARY.

=Acquired characters.=—_See_ Somatogenetic characters.

=Amphigony= (=Häckel=).—Sexual reproduction.

=Amphimixis= (=Weismann=).—The mingling of the hereditary substances of two individuals in an act of sexual union.

=Ancestral germ-plasm.=—_See_ p. 123.

=Asexual Reproduction.=—In which there is no liberation of special germ cells containing the potentiality of the adult organism, but in which the same object is effected by the liberation of buds, overgrowths, &c., which develop into the parent form. There are many forms of a-sexual reproduction.

=Atavism.=—The abnormal occurrence in existing species of characters which were peculiar to ancestral species, e.g., see _Darwin and after Darwin_, 2nd ed., Part I, p. 94.

=Biophore.=—_See_ p. 123.

=Blastogenetic characters.=—_See_ Plasmogenetic characters.

=Calyx.=—The outermost covering of the flower, which protects it before opening. Its position and precise function vary.

=Cell nucleus.=—A spherical or ovoid body embedded in the cell protoplasm, which has important functions in cell division and in reproduction. It consists of chromatin and achromatin. There are often several nuclei in one cell, whilst some cells have not been shown to have a nucleus at all.

=Cessation of Selection= (=Romanes=).—_See_ Panmixia.

=Chromatin threads.=—Immediately before a cell divides the nucleus is resolved into chromatin fibres or threads and an achromatin matrix. These chromatin fibres are then marshalled into either rods or loops, &c., as the division of the cell proceeds (see _Darwin and after Darwin_, figs. 36, 37, and 38). Subsequent changes in the threads conclude the division (for a description of which consult the account above).

=Chromosomes.=—_See_ Chromatin threads.

=Compositae.=—Plants in which the inflorescence consists of numerous small flowers brought together into a dense head, the base of which is enclosed by a common envelope (e.g. the Daisy, Dandelion, &c.).

=Congenital characters.=—_See_ Plasmogenetic characters.

=Conjugation.=—This term is applied to a process observed in the Protozoa (q. v.), which seems to correspond to the sexual reproduction of the Metazoa (q. v.). The majority of the Protozoa cannot long continue to reproduce themselves a-sexually without becoming degenerate, or rather without becoming altogether extinct. Two individuals (as a rule) consequently unite either temporarily or permanently. In the former case, an exchange of material is effected; and in the latter, complete fusion takes place.

=Correlation.=—The normal coincidence of one phenomenon, character, &c., with another.

=Cytoplasm.=—_See_ pp. 30 and 32.

=Determinant.=—_See_ p. 123.

=Ectoblast.=—Syn. of epiblast and ectoderm. The general result of the division of a fertilized ovum is a two-layered ball of cells (a gastrula). The outer layer is called the ectoblast and the inner layer the entoblast. (See _Darwin and after Darwin_, p. 137 _et seq._).

=Embryology.=—Hence embryogenesis, &c. The study of the development or the early growth of the individual.

=Entoblast.=—Syn. of hypoblast and endoderm. _See_ Ectoblast.

=Epigenesis= (=Harvey=).—The theory that organisms are formed by the development of the egg itself, and not by the expansion of a miniature within the egg (preformation).

=Fallopian Tubes.=—The tubes through which the spermatozoa pass to effect fertilization, and through which the ova pass from the ovary to the uterus.

=Fission.=—Syn. of fissiparous separation. The breaking into two (without karyokinesis—q. v.) of a cell, which has, by overgrowth, disturbed its physiological equilibrium. This process is almost mechanical.

=Formative material.=—_See_ p. 56.

=Gemmation.=—That form of a-sexual reproduction known as budding.

=Gemmules= (=Darwin=).—Minute granules, formed by the division of the general body-cells, which are supposed to be dispersed throughout the entire system. These themselves multiply by division, and are collected from all parts of the body to constitute the sexual elements.

=Germ-plasm.=—_See_ p. 32.

=Hydroids.=—Belong to a division (Hydrozoa) of the stinging-animals or Coelenterata. They occur both in the sea and in fresh water, and are solely polypoid (i.e. tubular and tentacled).

=Hydromedusae.=—Also Hydrozoans. Hydroid colonies with special sexually reproductive persons, which are often liberated as floating bells or discs.

=Idio-plasm= (=A and B=).—_See_ pp. 31 and 32.

=Ids.=—_See_ p. 123.

=Invertebrata.=—Animals with a dorsal heart and without a backbone.

=Karyokinesis.=—The changes which are observed in the nucleus both immediately before and after cell division. _See_ Chromatin threads.

=Lamarckian factors.= _See_ Somatogenetic characters. _Also_ Neo-Lamarckians.

=Metaphyta.=—Multicellular plants (q. v.).

=Metazoa.=—Multicellular animals (q. v.).

=Micellae= (=Nägeli=).—_See_ Molecules, with which they are identical.

=Microaomata.=—The protoplasm of certain vegetable cells is in places characterized by the presence of minute corpuscles, which may be regarded as part of the protoplasm, and are certainly of a protoplasmic nature. These are termed Microsomata.

=Molecules= (=Weismann=).—_See_ p. 122.

=Multicellular organisms.=—Organisms composed of many cells, as distinguished from the Unicellular organisms, where each individual is constituted of only one cell.

=Natural Selection.=—Survival of the Fittest in the struggle for existence. For a full account of the process see _Darwin and after Darwin_, p. 251 _et seq._

=Neo-Darwinians.=—Those who believe that Natural Selection has been the only modifying influence in the evolution of species, and that the material for its action has been only plasmogenetic characters (q. v.).

=Neo-Lamarckians.=—Those who hold that organic evolution has been effected solely by means of the occurrence and preservation (inheritance) of somatogenetic characters (q. v.).

=Nuclear Thread or Loops.=—_See_ Chromatin threads.

=Nucleo-plasm.=—_See_ pp. 30 and 32.

=Nucleus.=—_See_ Cell nucleus.

=Nutritive congenital characters.=—_See_ p. 64.

=Ontogenetic grades.=—_See_ p. 35.

=Ontogeny.=—The life history of the individual, as distinguished from the ancestral history of the race (Phylogeny).

=Ova.=—Eggs—the product of the female reproductive gland (ovary or ovarium).

=Ovule.=—The seed in its earliest condition.

=Pangenesis= (=Darwin=).—The theory of Heredity by gemmules (q. v.).

=Panmixia= (=Weismann=).—The condition of free intercrossing, i.e. where Natural Selection (q. v.) cannot act.

=Parthenogenesis.=—A degenerate form of sexual reproduction, in which the egg develops without having been fertilized by the male element.

=Phylogeny.=—The ancestral history of the race, as distinguished from the life history of the individual (Ontogeny).

=Physiological Units= (=Spencer=).—Special units which it is inferred a plant or animal of any species is made up of, and in all of which dwells the intrinsic aptitude to aggregate into the form of that species.

=Plasma.=—The constituent material of cells, e. g. germ-plasma (of sexual-cells), somatoplasma (of body-cells).

=Plasmogenetic characters.=—Variations due to admixtures of germ-plasm in acts of sexual fertilization (and therefore present at birth), as distinguished from somatogenetic characters—variations which have been acquired independently of germ-plasm. _See_ Somatogenetic characters.

=Polar bodies.=—Before an egg is fertilized the nucleus moves towards the periphery and divides twice. The two cells that are thus formed are the polar bodies. The extrusion of polar bodies is _probably_ universal among animals, but only one polar body is extruded from parthenogenetic ova. See _Darwin and after Darwin_, pp. 125 and 126.

=Preformation.=—The old conjecture (1672—Malpighi) that the development of an embryo was merely the expansion or unfolding of a miniature of the adult within the egg.

=Protophyta.=—Unicellular plants (q. v.).

=Protoplasm.=—Living matter.

=Protozoa.=—Unicellular animals (q. v.).

=Representative Congenital characters.=—_See_ p. 65.

=Reversion.=—_See_ Atavism.

=Rudimentary Organs.=—Usually considered a synonym of the term “vestigial characters,” and is the name under which are included all those organs which, either from having become useless or from other causes, have been much reduced in size, e.g. the muscles of the external ear in man (see _Darwin and after Darwin_, p. 76), &c. Latterly the former expression has been used to describe organs in process of development (e.g. the electric organ of the skate—_loc.cit._, p. 365 _et seq._), whilst the latter is made to embrace all those organs in process of elimination.

=Soma.=—A general term descriptive of the whole mass of the body-cells of an organism.

=Somatic-idio-plasm.=—_See_ p. 32.

=Somatogenetic characters.=—Characters _acquired_ by the soma (i. e. variations acquired after birth by the action of the environment), as distinguished from characters _produced_ and potentially present from the first by a union of two masses of germ-plasm—plasmogenetic characters (q. v.).

=Somatoplasma-plasm.=—_See_ p. 32.

=Specialized congenital characters.=—_See_ p. 65.

=Spermathecae.=—Organs for the storing of the seminal fluid received in copulation.

=Spermatogenesis.=—The precise development of spermatozoa.

=Spermatozoa.=—The essential elements in the male seminal fluid, and secreted by the testis—the male reproductive gland.

=Stirp= (=Gallon=).—_See_ p. 58.

=Telegony.=—_See_ p. 141.

=Unicellular Organisms.=—Organisms composed of a single cell only, as distinguished from those consisting of aggregations of cells—Multicellular organisms.

=Vertebrata.=—Animals with a backbone and a ventral heart.

=Vestigial Organs.=—_See_ Rudimentary organs,

=Xenia.=—_See_ p. 141.

INDEX.

A.

Acquired characters, definition of, 5; inheritance of, 6, 15, 49, 57, 60, 67, 69, 71, 81, 83-84, 93-96, 104, 107, 110-111, 127, 173, _et seq._; Galton on inheritance of, 62, 106.

Adaptive development, Weismann on, 19.

Algae, De Vries on the chromatophores of, 83, 111.

Amphigony, the cause of individual hereditary variation, 91, 100-101.

Amphimixis, _see_ Sexual propagation.

Ancestral germ-plasm, 123.

Atavism, 3, 91, 105.

B.

=Bary, De=, on Weismann’s theory, 152.

Basidiomycetes, 90.

Begonia, regeneration in, 4, 52.

Biophores, 123.

Body-cells, and germ-cells, 29.

=Brooks=, theory of heredity, 2.

Bud-variation, 90, 94, 96, 98-99; Weismann on, 95, 97, 161; Fritz Müller on, 95.

Butterflies, climatic varieties of and Weismann’s theory, 67-68, 127-128.

C.

=Candolle, De=, on inheritance of acquired characters in plants, 93. “Carriers of Heredity,” 32, 38, 70, 78, 122.

Cessation of Selection, _see_ Panmixia.

Chromatophores, of Algae, 83, 111.

Compositae, pollen of, 5.

Congenital variations, definition of, 5; inheritance of, 6, 110; sexual propagation, the cause of, 11; Darwin on, 13; origin of, 23, 25, 100, 102; nutritive congenital changes, 64; examples of, 64; specialized congenital changes, 65; representative congenital changes, 65; Galton on, 134.

Continuity of germ-plasm, _see_ Germ-plasm.

Crustacea, and the inheritance of acquired characters, 94.

Cuttings, and bud-variation, 98.

_Cytisus adami_, grafting of, 127.

D.

=Darwin, Charles=, and Pangenesis, 2, 26; arguments in favour of pangenesis, 3, 59; on the cause of congenital variations, 13; comparison of his theory of heredity with that of Weismann, 52, 55, 73, 92, 105-106, 115, 133, 173 _et seq._; on germ and somatic-cells, 76; on the influence of pollen upon somatic tissues, 79-80; on graft-hybridization, 83; on bud-variation, 95; on the causes of variation, 102, 161; on the inheritance of acquired characters, 107, 111-112; on Xenia, 144; on sexual union, 154.

Death, Weismann on the origin of, 8, 10; in plants, 10.

Determinants, 123.

Direct action of environment, on unicellular organisms, 15, 23.

E.

=Elsberg=, theory of heredity, 2.

Environment, direct action of on Protozoa, 15.

Evolution, _see_ Organic evolution.

F.

=Flint, Prof. Austin=, on Telegony, 204.

=Focke=, on Xenia, 141, 144.

“Formative material,” and germ-plasm, 56.

Fungi, Prof. Vines on Basidiomycetes, 90.

G.

=Galton, Francis=, theory of heredity (stirp), 2; and Weismann’s, 51, 58-59, 69, 73, 92, 105-106, 108, 115, 129, 130 _et seq._; on gemmules, 60; on inheritance of acquired characters, 62, 69, 107; and stability of the material basis of heredity, 63; on origin of sexual reproduction, 103, 167.

=Gärtner=, on Malva, 80; on inheritance of acquired characters in plants, 93.

Gemmules, 2; Darwin on the size of, 4; and germ-plasm, 52, 55, 58, 92, 105; and stirp, 58; Galton on, 60.

Generative cells of the Hydromedusae, Weismann on, 71, 109; example of continuity of germ-plasm, 72-73.

Germ-cells, and body-cells, 29, 75-77; nucleo-plasm of, 30; number of, 43, 45.

Germ-plasm, Weismann’s theory of, 5, 105, 173 _et seq._; immortality of, 9, 24; continuity of, 9, 18, 49, 56-67, 69-70, 72, 75, 78, 86-87, 104-105, 109-110, 114, 120, 168; differences in, 12; origin of, 17; independence of, 19; and natural selection, 21; stability of, 22, 49, 57, 66, 86-89, 91-93, 99-100, 104-105, 109, 112-114, 151 _et seq._; lodged in nucleus, 29; and somato-plasm, 29, 81, 110; the modification of, 36; examination of Weismann’s theory of, 48; Weismann’s theory of and Pangenesis, 52; and gemmules, 52, 55, 58, 105-106, 121; multiplication of in the general cellular tissues of plants, 53; De Vries on, 54; Differentiation of, 55; and “formative material,” 56; and stirp, 58-59, 61, 75, 106; and somatic-idioplasm, 69; as a basis of heredity, 70; ancestral germ-plasm, 123.

Grafting, and the effect of the somatic-tissues on the germinal elements, 81-82; Darwin on, 83; and bud-variation, 98; Weismann on, 126.

H.

=Häckel=, theory of heredity, 2.

=Hartog, Prof. M.=, on Weismann, 155; on sexual propagation, 166-167.

Healing of wounds, 34.

=Henslow, Rev. G.=, on regeneration in plants, 53.

Heredity, various theories of, 2, 49, 70; statement of Weismann’s theory of, 17; modification of Weismann’s theory of, 28, 46, 52, 65, 68, 75, 163 _et seq._; the nucleus and, 29; “carriers of,” 32, 38, 70, 78, 122; theory of and histology, 38; examination of Weismann’s theory of, 48, 105, 117; comparison of Weismann’s, Darwin’s, and Galton’s theories of, 51, 105-106; criticism of Weismann’s theory of by Strasburger, 51; the material basis of, 61, 63.

=Hertwig, O.=, theory of heredity, 2; on polar bodies, 46, 125.

=Hildebrand=, or effect of pollen upon somatic tissues (Xenia), 80; on Orchideae, 80.

=His=, theory of heredity, 2.

=Hoffmann=, on the inheritance of acquired characters, 93-4, 114.

Hydromedusae, Weismann on generative cells of, 71, 109; illustrate continuity of germ-plasm, 73-73.

I.

Identical twins, 41.

Idio-plasm, Nägeli’s term, 31; A and B, 31-32; self-multiplication of, 34; amount of idio-plasm A in the nucleus, 40.

Ids, 123.

Individual differences, Weismann, 39, 41, 43.

Influence of a previous sire upon the progeny of the same dam, _see_ Telegony.

Influence of external conditions, _see_ Acquired characters.

Influence of pollen upon somatic tissues, _see_ Xenia.

Inheritance of acquired characters, _see_ Acquired characters.

Invertebrates, Weismann on sexual apparatus of, 72, 74, 109.

J.

Jelly-fish, regeneration in, 4.

=Jordan=, on inheritance of acquired characters in plants, 93.

K.

Karyokinesis, 37.

L.

=Lamarck=, Weismann and, 16, 21.

Lamarckian factors, importance of, 57, 59, 62, 65, 67, 69, 82, 106-108, 111-112, 128, 147.

Life, duration of, 7, 10.

M.

=Malingié-Nouel=, on Telegony, 193 _et seq._

Malva, Gärtner on, 80.

=Maupas=, on the Protozoa, 101, 148.

Metazoa and Metaphyta, cause of mortality of, 7, 24, 148; relation of progeny to parents in, 16; transmission of acquired characters in, 16; propagation in, 51.

=Mivart=, on inheritance of acquired characters, 94.

Molecules, 54, 123.

=Morton, Earl of=, on Telegony, 192.

=Müller, Fritz=, on bud-variation, 95.

Multicellular organisms, _see_ Metazoa and Metaphyta.

N.

=Nägeli=, theory of heredity, 2; and idio-plasm, 31, 187; and germ-plasm, 36; on inheritance of acquired characters in plants, 93.

Natural selection, the cause of death, 8; action of, 20; the material for the operation of, 13, 57; not the cause of sexual propagation, 13-14; and the Protozoa, 15, 101-102; and germ-plasm, 21; sole cause of organic evolution, 25, 59, 111, 114.

=Nouel, Malingié=, on Telegony, 193 _et seq._

Nucleo-plasm, of germ and somatic cells, 30.

Nucleus, alone contains germ-plasm, 29; contains two substances, 33; and heredity, 37; and polar bodies, 40; amount of idio-plasm A in, 40.

Nutritive congenital changes, 64.

O.

Orchideae, Hildeband on, 80.

Organic evolution, the cause of, 25; Weismann’s theory of, 26, 48, 50, 58, 66, 68, 87, 100, 104, 106-108, 114-115, 147.

Ova, Weismann on the size of, 39.

P.

=Pallas=, on variability, 154.

Pangenesis, Darwin’s theory of, 2, 26; and Weismann’s theory of, 52, 55, 71, 73, 121; and Panmixia, 59-60; Galton on, 60.

Panmixia, and Pangenesis, 59-60.

Parthenogenetic organisms, and natural selection, 15; no congenital variations in, 72, 75.

Parthenogenetic ova, Weismann on, 45, 89, 91, 109.

Phylogenesis, 34.

Physiological isolation, of germ-cells, 74.

Plants, reproductive cells of, 74; influence of pollen upon somatic tissues of (Xenia), 78-80; bud-variation in, 90, 94-99; Hoffmann’s investigations on the inheritance of acquired characters in, 93.

Polar bodies, Weismann on, 40, 46, 125; examination of Weismann’s explanation of, 42; O. Hertwig on, 46, 125.

Protophyta, natural selection and, 114.

Protozoa, immortality of, 7; and natural selection, 15, 114; origin of species of, 15, 102; action of environment on, 15; Maupas on, 101.

R.

Regeneration, in sea-anemones and jelly-fish, 4, 35; of an entire organism, 34; Weismann on, 51 _et seq._; in Begonia, 52; Rev. G. Henslow on, 53; and stirp, 59.

Rejuvenescence, 166.

Representative congenital changes, 65.

Reproduction, essential meaning of sexual, 8, 11; in the Protozoa, 16; somatic, 35.

Reproductive elements, potential immortality of, 9; of Vertebrates and Plants, 74.

Reversion, 3, 91, 105.

=Roux=, on the principle of “struggle,” 139.

S.

Sea-anemones, regeneration in, 4.

Sexual apparatus of Invertebrates, Weismann on, 72, 74.

Sexual-cells and somatic-cells, 75-77, 81, 84.

Sexual propagation, essential meaning of, 8, 11, 87; sole cause of congenital variations, 12, 89-90, 102, 135, 141, 153, 158; did not arise through the agency of natural selection, 13-14; in multicellular organisms, 51; Galton on the origin of, 103; in _Cytisus adami_, 127.

Significance of sexual reproduction, _see_ Sexual Reproduction.

Somatic-cells, nucleo-plasm of, 30; and sexual cells, 75-77, 81, 84.

Somatic-idio-plasm, 32-33; and germ-plasm, 69.

Somatic reproduction, 35, 52.

Somato-plasm and germ-plasm, 29.

Specialized congenital changes, 65.

Species, Weismann on the origin of new, 100-101.

=Spencer, Herbert=, theory of heredity, 2; on Telegony, 191 _et seq._

Stability of germ-plasm, _see_ Germ-plasm.

Stirp, and gemmules, 58-59, 61; and somatic tissues, 60; and the germinal cells of Hydromedusae, 73; and germ-plasm, 75, 92, 106, 133.

=Strasburger=, on Weismann’s theory of heredity, 51; on the origin of sexual propagation, 167.

_Stylonichia_, Maupas on, 101.

Summary, 103.

T.

Telegony, 77-79, 110, 141 _et seq._, 191 _et seq._

Transmission of acquired characters, _see_ Acquired characters.

Twins, identical, 41.

U.

Unicellular organisms, reproduction of, 16; action of environment on, 23, 147 _et seq._; potentially immortal, 23; natural selection and the, 24, 57, 114; and the origin of hereditary individual variations, 100.

V.

Variation, _see_ Congenital variations, Acquired characters, &c.; Darwin on the causes of, 102; Weismann on the origin of, 153.

Vertebrates, reproductive cells of, 74.

Vestigial organs, persistence of, 91.

=Vines, Prof. S.=, criticism on Weismann, 14, 75, 90, 99, 152, 178; on the Basidiomycetes, 90.

=Vries, De=, theory of heredity, 2; on germ-plasm, 54; on the chromatophores of Algae, 83, 111; on Xenia, 144.

W.

=Weismann, Prof. August.=, theory of germ-plasm, 5, 17, 173 _et seq._; on the duration of life, 7, 10; on the essential meaning of sexual propagation, 11, 103, 135, 141; on natural selection as the origin of sexual reproduction, 14; on Prof. Vines’ criticism, 14, 90, 99, 178 _et seq._; on the Protozoa and natural selection, 15, 102; on Lamarck, 16; on adaptive development, 19; and natural selection, 21; summary of theory of germ-plasm, 23; theory of organic evolution, 26, 48, 50, 58, 66, 68, 87, 100, 104, 106-108, 114-115, 147; modifications of theory of heredity, 28, 46, 52, 65, 68, 75, 163 _et seq._; and of self-multiplication of idio-plasm, 34; on “ontogenetic grades,” 35, 53; on the modification of germ-plasm, 36; on chromatin, 38; on individual differences, 39, 41, 43; on the size of ova, 39; on polar bodies, 40, 42, 46, 125; on the number of germ-cells, 44-45; on parthenogenetic ova, 45, 89, 91; examination of his theory of germ-plasm or heredity, 48, 85; on the stability and continuity of germ-plasm, 49, 63, 66, 86-89, 91-93, 99-100, 103-105, 107, 109-110, 112-114, 120, 151, 158; comparison of his theory with those of Darwin and Galton, 51, 58; on Strasburger’s criticism of his theory, 52; on the multiplication of germ-plasm in the general cellular tissues of plants, 53; on regeneration in plants, 53; anticipated by Galton, 59, 68; and Galton, 63, 130 _et seq._; on transmission of acquired characters, 67, 83, 96, 111, 127; and his critics, 70; on the Hydromedusae, 71, 109; on the sexual apparatus of Invertebrates, 72; and the influence of germ-cells upon somatic tissues (Telegony and Xenia), 80-81, 196 _et seq._; and the significance of grafting, 81-82, 126; and vestigial characters, 92; on Hoffmann’s investigations, 93; on bud-variation, 95, 97, 161; on the origin of hereditary individual variations, 100-101; on the origin of new species, 101.

Wounds, healing of, 34.

X.

Xenia, 78-81, 110, 141, 144, _et seq._

THE END.

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FOOTNOTES:

[1] Considerable portions of this chapter have already appeared as an article in the _Contemporary Review_ for May, 1890. My thanks are due to the editor for kindly allowing me to reproduce them here.

[2] In as far as these sundry theories of heredity are not more or less intermediate between those of Darwin and Weismann, the differences have reference either to points of comparative detail, or else to the introduction of ideas derived from chemistry and physics—whereby it is sought to show that the principles of chemical combination and of rhythmic vibration may have a more or less considerable share in the matter. For my own part I do not see that the introduction of such ideas has been of any avail in helping—even hypothetically—to explain the phenomena of heredity; and therefore I do not deem it worth our while to consider them.

[3] See Appendix.

[4] E.g., _Variation_, &c., vol. i. pp. 197, 398; vol. ii. pp. 237, 252.

[5] Since this chapter was written and sent as a contribution to the _Contemporary Review_, Professor Weismann has published in _Nature_ (Feb. 6. 1890) an elaborate answer to a criticism of his theory by Professor Vines (Oct. 24, 1889). In the course of this answer Professor Weismann says that he does attribute the origin of sexual reproduction to natural selection. This directly contradicts what he says in his _Essays_; and, for the reasons given in the text, appears to me an illogical departure from his previously logical attitude. I herewith append quotations, in order to reveal the contradiction.

“But when I maintain that the meaning of sexual reproduction is to render possible the transformation of the higher organisms by means of natural selection, such a statement is not equivalent to the assertion that sexual reproduction originally came into existence in order to achieve this end. The effects which are now produced by sexual reproduction did not constitute the causes which led to its first appearance. Sexual reproduction came into existence before it could lead to hereditary individual variability [i.e., to the possibility of natural selection]. Its first appearance must, therefore, have had some other cause [than natural selection]; but the nature of this cause can hardly be determined with any degree of certainty or precision from the facts with which we are at present acquainted.”—_Essay on the Significance of Sexual Reproduction in the Theory of Natural Selection._ English Translation, pp. 281-282.

“I am still of opinion that the origin of sexual reproduction depends on the advantage which it affords to the operation of natural selection.... Sexual reproduction has arisen by and for natural selection as the sole means by which individual variations can be united and combined in every possible proportion.”—_Nature_, vol. xli. p. 322.

How such contradictory statements can be reconciled I do not perceive; but they furnish a good example of the extreme laxity with which the term “natural selection” is used by ultra-Darwinians.

[6] The meaning of this term, however, as originally used by Nägeli, he so greatly changes to suit the requirements of his own theory, that I think it would have been better had he coined some new one.

[7] I think it is to be regretted that for this other kind of idio-plasm (i.e., idio-plasm-B) Weismann has not coined some distinctive name, or some distinctive prefix, such as that which he sometimes employs when speaking of the other kind (i.e., idio-plasm-A)—viz., “somatic-idioplasm.” Also, the interchangeable manner in which he uses his term “idio-plasm” with the term “ nucleo-plasm,” is somewhat confusing (e.g., pp. 217, 219, 220, 250, 251, &c.). I may add that the word “plasm” in all its combinations appears to me an unfortunate one, since it seems to betoken a substance that can be _seen_, instead of merely inferred. But, be this as it may, the following table of terms employed may be useful for ready reference:—

Nucleo-plasm = the whole contents of the nucleus of any cell.

Cytoplasm = all the other contents of any cell.

Idio-plasm-A = that portion of nucleo-plasm which “controls” a single cell.

Idio-plasm-B = that portion of nucleo-plasm which is destined to construct future cells.

Germ-plasm = undifferentiated idio-plasm-B.

Somato-plasm = idio-plasm-A + cytoplasm.

[8] See close of Appendix.

[9] See Part I, figs. 36, 37, and 38. The substance of this thread, in the various phases of its segmentation, is the “chromatin,” as there depicted, and so called because it takes a stain better than other parts of the nucleus—thus showing some distinctive character.

[10] For an account of the formation and expulsion of these bodies, see Part I, pp. 125-6. There is now no longer any doubt touching the statement there made as to the male-cell likewise parting with some of its nuclear substance prior to fertilizing the female.

[11] In the case of identical twins, both are probably always produced from the _same_ ovum.

[12] We have no means of estimating exactly the proportional number of cases in which this is possible, either among the lower or the higher plants; but it is certainly much greater than Weismann supposes. “How is it that all plants cannot be reproduced in this way?” he asks, and then adds,—“No one has ever grown a tree from the leaf of a lime or an oak, or a flowering plant from a leaf of the tulip or the convolvulus.” But I am told by botanists that the only reason why the phenomenon thus appears to be a rare one, is because it is not worth anybody’s while to grow plants in this way at a necessarily unsuitable season of the year. Thus, the Rev. George Henslow writes me:—“The fact is that _any_ plant will reproduce itself by its leaves, provided that the cells be ‘embryonic,’ (i.e., the leaf not too near its complete development), and that it be not too _thin_, so as to provide enough nutriment for the bud to form till it has roots.”

[13] _Intracellulare Pangenesis_, s. 55.

[14] I employ the term “particles,” instead of “molecules,” because although Weismann and his followers seem to prefer the latter term, I can scarcely imagine that they intend to use it in its original, or chemical, sense.

[15] This principle will be considered at some length in my next volume.

[16] Galton first published his theory in 1872 (_Proc. R. S._, No. 136), but presented it in a more complete form three years later (_Contemporary Review_, Dec. 1875, and _Journl. Anthropol. Inst._, 1875).

[17] _Journ. Anthropol. Inst._ 1875, p. 346.

[18] _Essays_, &c., 2nd ed., p. 105.

[19] _Essays_, &c., 2nd ed., p. 100.

[20] See for example, _Essays_, p. 229.

[21] On previous occasions, when inconsistencies have been brought to the notice of Professor Weismann by his critics, he has complained that sufficient allowance was not made for the fact of his having published his sundry essays at different times. This, of course, is a satisfactory answer in cases where criticism refers to a growing theory, the later additions to which supersede certain parts of the earlier construction. But clearly the answer is not available in cases where one set of statements, touching fundamental principles of the theory, are directly opposed to others. A logical contradiction is not affected by dates of publication, and where the contradictory statements have reference to the vital essence of a theory, it is equally impossible for the theory to comprise them whether they be presented simultaneously or successively.

[22] The possibility of any spermatozoa of the first impregnation surviving to take part in the second is excluded by the fact that the phenomenon occurs in mammals, and, apparently, may extend over two or three litters.

[23] Possibly the school of Weismann may simply refuse to accept the facts, which are confessedly rare, and, in many of the cases alleged, dubious. In other cases, however, the evidence is sufficient to have satisfied the cautious judgement of Darwin, who has discussed it in detail. Therefore, even if the Neo-Darwinians repudiate this evidence, at least they ought to state that such is the position which they adopt.

[24] _Nature_, Feb. 6th, 1890.

[25] _Nature_, vol. xl. p. 626.

[26] _Ibid._, vol. xli. p. 322.

[27] In his _Essays_ (vol. i. p. 282) Weismann says:—“If it could be shown that a purely parthenogenetic species had become transformed into a new one, such an observation would prove the existence of some new force of transformation other than selective processes, for the new species could not have been produced by these latter.” But now it has been shown that a purely parthenogenetic species can be transformed into a new one, and therefore it seems desirable to note that the observation does not so much as tend to prove the existence of some new force of transformation other than selective processes. For this most singular statement can only stand on a prior acceptance of Weismann’s own assumption, as to amphigony being the only possible cause of individual hereditary variation. Only if we have already, and with absolute certainty, embraced the whole Weismannian creed, could we consent to affirm that “natural selection is an impossibility in a species propagated by a-sexual reproduction.”

[28] What he says is:—“It was only after a greater or less number of generations had elapsed that a variable proportion of double flowers appeared, sometimes accompanied by changes in the leaves and in the colours of the flowers. _This fact admits of only one interpretation_:—the changed conditions at first produced slight and ineffectual changes in the idio-plasm of the individual, which was transmitted to the following generation.... Now, the idio-plasm of the first ontogenetic grade (viz., germ-plasm) alone passes from one generation to another, _and hence it is clear that the germ-plasm itself must have been gradually changed by the conditions of life, until the alteration became sufficient to produce changes in the soma, which appeared as visible characters in either flower or leaf_.”—_Essays_, pp. 426-7; italics mine.

[29] _Nature_, Nov. 14, 1889, p. 41.

[30] _Essays_, 2nd Ed., pp. 331-2.

[31] _Essays_, p. 296.

[32] In this connexion it ought to be observed that Darwin believed the causes of variation to be internal as well as external—or arising from “the nature of the organism” no less—or even more—than from “changed conditions of life.” But although he appears to have entertained the admixture of hereditary endowments in sexual unions as one of the causes of variation belonging to the former category, he expressly says that he did not regard it as the only, or even the main, cause. (See _Variation_, &c., vol. i, pp. 197, 398; vol. ii, pp. 237, 252.)

[33] See above, p. 54, note.

[34] See _Darwin and after Darwin_, Part I, p. 129.

[35] It must always be remembered that the view adopted by Weismann touching the nucleus (and more especially the chromosomes) of a germ-cell being the sole seat of heredity, is still far from having been established.

[36] _Essays_, vol. ii. p. 122.

[37] _The Germ-plasm_, p. 342.

[38] _The Germ-plasm_, p. 342.

[39] See, however, p. 83, note.

[40] _Essays_, vol. i. p. 101. Italics mine.

[41] _The Germ-plasm_, p. 406.

[42] Galton, _loc. cit._, pp. 343-344.

[43] Professor Weismann still maintains that there is a further important distinction between the theories of pangenesis and germ-plasm, in that the one is pre-formative while the other is epigenetic. But I am still unable to perceive that such is the case. He argues, indeed, that his new doctrine of determinants emphasizes this distinction: the argument, however, appears to me radically unsound. For instance, he says, “The hereditary continuation in each part is pre-determined in each part from the germ onwards. The right and left ears could not possibly resemble each other, if the relative strength of the hereditary tendencies on both sides were not pre-determined for all parts of the child by the nature of the paternal and maternal idants.” Very well. But, if so, the theory of determinants is just as much pre-formative as is that of gemmules. Or, conversely, the latter is quite as epigenetic as the former. Both are alike _determinative_, while neither supposes that the determination is due to a pre-formed miniature of the future child in the fertilized egg of its mother; but to a particulate _representation_ in the latter of every heritable part of the former.

[44] By “germ” Galton means a carrier of heredity, which is capable of self-multiplication. In these fundamental respects, therefore, it is equivalent to a “gemmule” on the one hand and a “determinant” on the other. The three terms are so far synonymous.

[45] _Loc. cit._, p. 338.

[46] _Loc. cit._, p. 339.

[47] _The Germ-plasm_, pp. 199, 220.

[48] pp. 72-4.

[49] _The Germ-plasm_, pp. 383-386.

[50] Quoted from above, p. 78.

[51] _Morph. Journal_, vol. ii.

[52] See Appendix II.

[53] _Essays on Heredity_, vol. ii. pp. 193-4.

[54] See above, pp. 63-67.

[55] _Nature_, vol. xli. p. 322.

[56] _The Germ-plasm_, pp. 414-415. Italics Weismann’s.

[57] _Essays_, vol. i. p. 284.

[58] _The Germ-plasm_, p. 431.

[59] _Variation_ &c., vol. i. p. 398.

[60] _Ibid._, vol. ii. p. 242.

[61] _Nature_, May 11, pp. 28-29.—In 1891-2 Professor Hartog furnished a criticism of Weismann’s theory of Heredity (_Nature_, vol. 44. p. 613, and _Contemporary Review_, July, 1892). Although disputed at the time by some of Weismann’s followers in England, this criticism was one of unquestionable cogency, and has now been recognized as such by Weismann himself (_The Germ-plasm_, pp. 434-5). The main point of the criticism had been missed by previous critics of Weismann, and consisted in revealing an important “difficulty” inherent in the structure of the theory itself. How far this criticism had the effect of causing Professor Weismann to abandon his theory of variation being exclusively due to amphimixis, as Professor Hartog appears to think (_Nature_, May 11, 1893, p. 28), is immaterial. But it must be observed that as far back as February, 1890, Professor Weismann in his answer to Professor Vines’ criticism wrote the passage already quoted on page 152.

[62] It is almost needless to say that no fault is to be found with Weismann for having thus reversed his opinion touching one of his fundamental postulates. Consistency is no merit in a man of science; and least of all where matters of such high speculation are concerned. I think, however, that it is open to question whether an author of any kind should suffer an elaborate system of theories to be published and translated, at the very time when he is himself engaged in producing another work showing the untenable character of their basal premises. At any rate, it would have saved his English readers no small trouble and confusion, if Weismann had added notes to the translations of his essays on _Polar Bodies_, on _The Significance of Sexual Reproduction_, and on _Amphimixis_, to the effect that he had abandoned some of their most distinctive features before the translations had gone to press.

[63] See especially pp. 86-89. All that is there said about the unicellular organisms is not, in the present connexion, affected by Weismann’s change of view with regard to them. We have only to substitute “primordial” or “protoplasmic” for “unicellular,” and nearly all the points of the criticism remain.

[64] Professor Weismann has now considered more fully than heretofore the phenomena of bud-variation (_The Germ-plasm_, pp. 439-442); but as he continues (though with diffidence) to take substantially the same view of them as that which I have already quoted on pp. 95-96, it is needless for me to re-discuss the matter here.

[65] “Rejuvenescence” means the renewal of vital energies which is supposed to result from a fusion of the contents of two cells. For an excellent discussion of this and the other theories on the object of sexual propagation, see a brief article by Professor Marcus Hartog, in the _Contemporary Review_ for July, 1892. Since then Weismann has published _The Germ-plasm_, and here his main argument against this theory is that tens, or even hundreds of generations of unicellular organisms have been observed to succeed one another before any act of conjugation takes place. But I cannot see that it signifies how many generations may in different species be proved capable of resulting from a single act of conjugation. Weismann himself now accepts the analogy between cell-proliferation as resulting from conjugation in unicellular organisms, and from fertilization in multicellular. But even three hundred generations of the former can scarcely be regarded as equal to all the “ontogenetic stages” of the latter.

[66] This view of the function of sexual propagation is now universally ascribed to Strasburger, and it is quite true that he has independently adduced it. But as this was not done until about ten years after it had been published by Galton, I have designedly associated the idea with Galton’s name. The following are the words in which it was announced by him:—

“The necessity of a system of double parentage in complex organisations is the immediate consequence of a theory of organic units and germs, as we shall see if we fix our attention upon any one definite series of unisexual descents, and follow out its history. Suppose we select, cut off, and plant the second bud, then after it has grown to maturity we similarly take the second of _its_ buds, and so on consecutively. At each successive stage there is always a chance of some one or more of the various species of germs in the stirp dying out, or being omitted; and of course when they are gone they are lost for ever, and are irreplaceable by others. From time to time this chance must fall unfavourably, and will cause a deficiency in some of the structural elements, and a consequent deterioration of the race. If the loss be vital, this particular line of descent will of course be extinguished at once; but on the more favourable supposition, the race will linger on, submitting to successive decrements in its constituent elements, until the accumulation of small losses becomes fatal.”—_loc. cit._, p. 333.

Galton also points out a further advantage that is secured by “amphimixis,” and one which shows the non-necessity of what remains of Weismann’s theory of polar bodies, thus:—

“There is yet another advantage in double parentage, namely, that as the stirp whence the child sprang can only be half the size of the combined stirps of his two parents, it follows that one half of his possible heritage must have been suppressed. This implies a sharp struggle for place among the competing germs, and the success, as we may infer, of the fitter half of their numerous varieties.”—_loc. cit._, p. 334.

[67] In fact, it seems to me that this is the sole supposition whereby it can be held that sexual propagation has been developed both “_by_” and “_for_” natural selection, in order to supply variations as material for the action of this principle. Natural selection cannot thus supply the conditions to its own activity, if, as Weismann supposes, there is but one purpose for it to subserve (see above, pp. 13-15). But, if it is acting for more than one purpose, the “by” and the “for” argument may hold.

[68] I find that a passage explaining the sense in which I use these terms has been accidentally omitted from Chapter III, where they are first introduced; and, as the sheets of that chapter have been already printed off, I here supply the omission. The terms in italics are not Weismann’s, and I have employed them merely for the purpose of giving precision to his views. By “_absolute_ stability of germ-plasm” I mean to indicate that degree of stability which he has hitherto postulated as the necessary basis for his doctrine of heritable variations being solely due to admixtures of germ-plasm in sexual unions. By “_perpetual_ continuity of germ-plasm” I intend to denote that amount of continuity which he still postulates as the necessary basis for his correlative doctrine touching the non-inheritance of acquired characters.

[69] _Essays_, pp. 76-77, from which the following quotations are likewise taken _seriatim_.

[70] “Or, more precisely, they must give up as many molecules as would correspond to the number of the kind of cell in question found in the mature organism.” Of course by “molecules” Weismann means what Darwin does by “gemmules.”

[71] If there are such things as gemmules, it appears to me to follow that the only physiological distinction between the reproductive glands and glands in general is, that the former discharge their products in the form of living cells. Even here, however, there appears to be one analogous case in those salivary glands which discharge the so-called salivary corpuscles—i.e., nucleated cells, undergoing amoeboid changes of form, and exhibiting the movements of living protoplasm in their interior.

[72] _Variation_, &c., 2nd ed., vol. ii. pp. 374-6.

[73] _Nature_, vol. xl. p. 624. Weismann’s answer to this and other parts of Professor Vines’ criticism where the term “somato-plasm” occurs, will be considered later on.

[74] Weismann speaks disparagingly of Darwin’s theory as a “theory of _preformation_” (p. 316). “We must assume,” he adds by way of explanation, “that each single part of the body at each developmental stage is, from the first, represented in the germ-cell as distinct particles of matter, which will reproduce each part of the body at its appropriate stage as their turn for development arrives.” But must we not likewise “assume” exactly the same thing in the case of Weismann’s own theory? To me, at any rate, it appears that the description is quite as appropriate to germ-plasm as it is to gemmules. Nor can I see any distinction, even where he seeks to draw it more expressly, as for instance—“Every detail in the whole organism must be represented in the germ-plasm by its own special and peculiar arrangement of the groups of molecules, ... not indeed as the pre-formed germs of structure (the gemmules of pangenesis), but as variations in its molecular constitution.” [_Essays_, p. 194.] Again, on page 325 he gives a foot-note explaining the distinction by alluding to the controversy between the preformationists and epigenesists. But the theory of pangenesis does not suppose the future organism to exist in the egg-cell _as a miniature_: it supposes merely that every part of the future organism is represented in the egg-cell by corresponding material particles. And this, as far as I can understand, is exactly what the theory of germ-plasm supposes; only it calls the particles “molecules,” and seemingly attaches more importance to the matter of variations in their arrangement or “constitution,” whatever these vague expressions may be intended to signify.

[75] ‘Philosophical Transactions of the Royal Society for the Year 1821,’ Part I. pp, 20-24.

[76] Readers who may happen to be acquainted with De Vries’ important essay on heredity will perceive how well this suggestion fits in with his modification of Pangenesis.

[77] As already indicated, I cannot gather from his remarks on the subject which, if any, of the alternative interpretations of the phenomena that we are considering Mr. Spencer adopts. From the following sentences it would appear that he assigns yet a third interpretation, _and this as the only possible one_. For he says of these phenomena: “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” (_Contemporary Review_, March, p. 452). This appears to mean that the influence of a previous sire can only be explained by supposing that the developing embryo inoculates the somatic tissues of its mother with hereditary material derived from its father, and that the maternal tissue afterwards reflect some of this material (or its influence) to the still unripe ovarian ova. If this be the hypothesis intended, it seems to me more complex than any of the three which I have suggested. But, be this as it may, we certainly cannot agree that such an hypothesis is “proved” by the facts, or that the latter “necessitate” the inference as to its being some of the _embryo’s_ germinal matter which enters the unripe ova.

[78] “A Text Book of Human Physiology.” By Austin Flint, M.D., LL. D. Fourth edition. New York: D. Appleton & Co. 1888. Page 797.