320 



NATURE 



[Feb. 6, 1890 



problem, and have thus been compelled to formulate 

 some fundamental principles for the explanation of the 

 phenomena ; but no one can be more convinced than I 

 how far we are from a definite and complete explanation, 

 not only of " every detail," but also of " the more general 

 phenomena." My endeavour was to put forth a real, in 

 place of the previous ideal, theory ; and on this ground I 

 took pains to make only such suppositions as might pos- 

 sibly correspond to actual facts. There certainly is a 

 material carrier of heredity in the ovum ; it certainly can 

 be transported from nucleus to nucleus ; it certainly can 

 be modified in the process, or can remain the same ; and 

 even the supposition that it is able to stamp its own cha- 

 racter on the cell contains nothingwhich seems to us impos- 

 sible and non-existent ; on the contrary, we are able now to 

 state that it is so, even if we do not understand in what 

 wise it happens. My hypothesis relative to the quiescent 

 state of germ-plasma also rests on a basis of fact ; we 

 know that ancestral characteristics may be transmitted 

 in a latent condition, and that the process of transmis- 

 sion is bound up with a substance, the idioplasma ; there 

 must therefore actually be an inactive stage of idioplasma. 



If it could be shown that upon such principles an ex- 

 planation of heredity is attainable, we should have made 

 a distinct advance upon the ideal theory of pangenesis 

 which is founded on unreal hypotheses. Possibly it is 

 upon the path which I have opened up that we shall 

 gradually attain a satisfactory solution of the numerous 

 questions at issue ; possibly further research will show 

 that it is not the right path, and must be abandoned ; no 

 one, it appears to me, can foretell this. My reflections 

 on heredity are not a conclusion, but a commencement — 

 no complete theory of heredity which claims to provide a 

 complete solution of all the problems at issue, but re- 

 searches which, if fortunate, may sooner or later, by 

 direct or circuitous paths, lead to a true appreciation of 

 the question, to a " real" theory. In the preface to the 

 English edition of my "Essays" I have stated this 

 expressly. 



I have also in that place distinctly insisted that the 

 book was not written as a whole ; that it consists rather 

 of a series of researches, the one growing out of the other, 

 and showing the development of my views as they shaped 

 themselves during the course of nearly a decade's work. 

 It is therefore unreasonable to extract ideas from an 

 earlier essay and apply them against a later one. I have 

 left them unaltered, and even " left certain errors of inter- 

 pretation uncorrected," because, if altered, their internal 

 connection could not have been understood. 



I believe that the objections which Prof. 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 \vhich they do not tally. I will en- 

 deavour to make this clear. In this second essay (1883) 

 I contrasted the body (soma) with the germ-cells, and ex- 

 plained 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 there- 

 fore 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 Stras- 

 burger 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 idioplasma, which 

 Nageli had enunciated in essentially different terms, to 

 the " Vererbungs-substanz " of the ovum-nucleus, and 

 laid down that the nuclear chromatin was the idioplasma 

 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 " somatoplasm," but distinguished, on the one 

 hand, the idioplasm or " Anlagen-plasma " of the nucleus 

 from the cell-body or " Cyloplasma," and, on the other,, 

 the idioplasm of the ovum-nucleus from that of the 

 somatic cell-nucleus ; I also for the future applied "germ- 

 plasm " to the nuclear idioplasm of ovum and spermato- 

 zoon, and" somatic idioplasm" to that of the body-cells 

 {e.g. p. 184). The embryogenesis rests, according to my 

 idea, on alterations in the nuclear idioplasma of the ovum, 

 or "germ-plasm" ; on p. 186, et seqq., is pictured the way in 

 which the nuclear idioplasm 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 idioplasma. 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 Prof. 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 hypo- 

 thesis that in segmentation it is not all the germ-plasm 

 {i.e. idioplasm 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 idioplasm, 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 remark- 

 able 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. Prof Vines says : — 

 " The fate of the germ-plasm of the fertilized ovum is. 

 according to Prof Weismann, to be converted in part into 

 the somatoplasm [!] 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 somatoplasm [!] 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 reasoji 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 Prof. Vines ; my germ-plasm or idioplasm of the 

 first ontogenetic grade is not modified into the somato- 

 plasm of Prof. Vines, but into idioplasm of the second, 

 third, fourth, hundredth, &c., grade, and every one im- 

 presses its character on the cell containing it. 



Prof. Vines also attacks my view of the idioplasmatic 

 nature of the nuclear substance (the chromatic grains) \ 

 and maintains that it is as easy to speak of the continuity 

 of the cell-body as of that of the nuclear substance, and 

 that the one may transmit heritable qualities to progeny 

 as well as the other. I quite understand that a botanist 

 may easily be led to this view ; and Prof. Vines is not the 



