HARDWICKE'S SCIENCE-GOSSIP. 



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is a difficulty which Professor Ray Lankester ex- 

 pressed so long ago as 1876, when contrasting Mr. 

 Spencer's theory with that of Pangenesis.* And 

 now we are certainly entitled to go further, and to 

 enquire why the effects of constantly performed 

 mutilations, which are not repaired, do not tend to 

 become inherited after many generations, as they 

 certainly ought to be on Mr. Spencer's theory. 

 Finally we ask — and ask in vain — for an explanation 

 of the fundamental facts of atavism, f 

 ■ Mr. Darwin's " Provisional Hypothesis of Pan- 

 genesis " differs very fundamentally from the theory 

 we have been hitherto considering. It distinctly 

 recognises the necessity of grappling with the two 

 questions which we have seen to be the fundamental 

 problems of heredity — the problems of transmission 

 and of development — and it answers these questions 

 in a clear and unmistakable manner. 



Mr. Darwin supposes certain organic particles 

 called gemimdes to be the specific bearers of here- 

 ditary tendencies. These are continually — at all 

 stages of development — being given off by every cell 

 in the body. The gemmules are continually circu- 

 lating throughout the body, and finally collect in the 

 reproductive cells. Each gemmule is a representative 

 of the cell from which it took its origin {at that 

 period of its life-history), and is capable, under proper 

 conditions, of developing into a similar cell. The 

 germ-cells, then, being simply collections of such 

 gemmules, possess the potentialities of new organisms 

 exactly similar to the old. J This is Mr. Darwin's 

 solution of the problem of transmission. The pro- 

 blem of development he solves as follows. The 

 gemmules representing any given stage of develop- 

 ment have a special affinity for the partially-developed 

 cells of the stage immediately preceding. They seek 

 out and unite with these, and are thus able to develop 

 in the right order their corresponding parts. This 

 extremely ingenious suggestion Mr. Darwin supports 

 by reference to the unerring accuracy with which 

 pollen of the right species alone develops pollen- 

 tubes when a number of different kinds are placed on 

 the stigma of a flower. 



The phenomena of atavism, Mr. Darwin explains 

 by supposing that some gemmules lie dormant for 



* "Advancement of Science," pp. 280-282. 



t It is hardly fair_ to Mr. Spencer to charge him, as is so 

 often done, with being too vague and general in his theory 

 of heredity. In the first place, he is not in the least vague, 

 •and the impression that he is usually arises from failure to 

 thoroughly understand his meaning. That his theory is 

 "general," is true, as we have already insisted ; but it should 

 be remembered that he expressly says "a positive explanation 

 IS not to be expected in the present state of biology. We can 

 look for nothing beyond a simplification of the problem." It 

 is, however, quite open to us to criticise the theory on the 

 ground of its being inconsistent with known facts ; and further, 

 to demand now a fuller and more special explanation of the 

 phenomena of heredity, as the result of the many years of 

 research which have elapsed since Mr. Spencer's words were 

 written. 



X "An organic being is a microcosm— a little universe, formed 

 of a host of self-propagating organisms, inconceivably minute 

 and numerous as the stars in heaven" ("Variation under 

 Domestication, vol. ii, p. 399). 



more or fewer generations, and suddenly, owing to 

 especially favourable conditions, are enabled to de- 

 velop into their corresponding structures. 



It will be seen that this theory explains the pro- 

 blem of transmission mainly by the hypothesis of the 

 redevelopment of new gemmules from the cells of the 

 body into which the former gemmules were developecL 

 It explains the problem of development, by supposing 

 that there has been 2. preformation * of distinct ^t'rwj 

 of structure, and that by means of the presence of 

 these the germ-cell is able to produce the organism. 



Mr. Darwin's theory explains with great readiness 

 most of the observed abnormal phenomena of 

 heredity, but it was to explain the supposed heredi- 

 tary effects of use and disuse that it was especially 

 constructed. This was indicated in the last paper 

 (p. 210), and it was there pointed out that Mr^ 

 Darwin was right in his belief that a theory on the 

 lines of Pangenesis would have to be ultimately 

 adopted, if acquired characters are inherited. Its 

 explanation of the problem of transmission by the 

 assumption of the redevelopment of the gemmules 

 from the cells of the body alone enables it to explain 

 the hereditary transmission of the modifications ac- 

 quired by those cells. The other theories of heredity 

 which profess to allow of such transmission — such 

 as Mr. Spencer's, depending on assumed absolute 

 solidarity of the organism, or the late Professor 

 Niigeli's, depending on cyclical development of idio- 

 plasm, which we shall consider presently — are ojjea 

 to even more serious and fundamental objections than 

 is Pangenesis. We are, I think, in a position to say 

 that if acquired characters are transmitted, a theory 

 of heredity not essentially differing from Pangenesis 

 will have to be adopted, and the difficulties — very 

 great difficulties — attaching to it will have to be 

 explained away somehow. 



The theory of Pangenesis has been often and 

 severely criticised ; it is not my ^purpose to give a 

 list of these criticisms here, but I shall consider three 

 which seem to me to be of special importance. First, 

 there is the argument about the inconceivable number 

 of gemmules that must exist in the fertilised egg-cell 



* Harvey, following Aristotle, enunciated the theory' of 

 epigenesis, to explain the process of development of the fer- 

 tilised ovum into the adult organism. He believed that the 

 various structures of the adult were formed by the successive 

 differentiations of a relatively homogeneous rudiment (the 

 fertilised ovum). Malpighi contradicted this on the ground of 

 having directly observed the body of the chick in the egg 

 during the early days of incubation. He unjustifiably assumed 

 that it existed in the egg as a whole be/ore incubation. Later 

 on his views were taken up and extended by Bonnet and 

 Haller, and became widely accepted. Bonnet, however, 

 modified his doctrine in later life, and looked upon the egg as 

 being only an "original preformation " of the body, not neces- 

 sarily an actual miniature of the latter. C. F. Wolff, in 1759, 

 entirely exploded the theory of "evolution," or "preforma- 

 tion" as generally understood, and re-established "epige- 

 nesis ;" but Darwin in his theory of pangenesis undoubtedly 

 revived the conception of the preformation of distinct germs of 

 structure, though not, of course, the idea of a miniature 

 organism in the ovum, but rather a conception akin to Bonnet's 

 later views. It is in this modified sense that we use the word 

 "preformation" and contrast it with pure "epigenesis," to 

 which Professor Weismann has conspicuously returned. 



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