PRESIDENTS ADDRESS. 19 



deuce by which somatists strive to prove their point, because I do not 

 know of any facts which are really decisive. That is to say, that though 

 they are explicable as due to somatic inheritance, they never seem to me 

 absolutely inexplicable on Weismann's hypothesis. But, as already pointed 

 out, it is not necessary to look for special facts and experiments, since if 

 the mnemic theory of ontogeny is accepted the development of every 

 organism in the world depends on somatic inheritance. 



I fully acknowledge the strength of Weismann's position ; I acknow- 

 ledge also most fully that it requires a stronger man than myself to meet 

 that trained and well-tried fighter. Nevertheless, I shall venture on a 

 few remarks. It must be remembered that, as Romanes ^ pointed out, 

 Weismann has greatly strengthened his theory of heredity by giving up 

 the absolute stability and perpetual continuity of germ-plasm. Germ plasm 

 is no longer that mysterious entity, immortal and self-contained, which 

 used to suggest a physical soul. It is no longer the aristocrat it was 

 when its only activity was dependent on its protozoan ancestors, when it 

 reigned absolutely aloof from its contemporary subjects. The germ-plasm 

 theory of to-day is liberalised, though it is not so democratic as its brother 

 sovereign Pangenesis, who reigns, or used to reign, by an elaborate system 

 of proportional representation. But in spite of the skill and energy 

 devoted to its improvement by its distinguished author, Weismannism 

 fails, in my opinion, to be a satisfactory theory of evolution. 



All such theories must account for two things which are parts of a 

 single process but may logically be considered separately : (i) The fact 

 of ontogeny, namely, that the ovum has the capacity of developing into a 

 certain more or less predetermined form ; (ii) The fact of heredity — the 

 circumstance that this form is approximately the same as that of the 

 parent. 



The doctrine of pangenesis accounts for heredity, since the germ-cells 

 are imagined as made up of gemmules representing all parts of the adult ; 

 but it does not account for ontogeny, because there seems to me no 

 sufficient reason why the gemmules should become active in a predeter- 

 mined order unless, indeed, we allow that they do so by habit, and then 

 the doctrine of pangenesis becomes a variant of the mnemic theory. 



The strength of Weismann's theory lies in its explanation of heredity. 

 According to the doctrine of continuity, a fragment of the germ-plasm is, 

 as it were, put on one side and saved up to make the germ-cell of the new 

 generation, so that the germ-cells of two successive generations are made 

 of the same matei'ial. This again depends on Weismann's belief that 

 when the ovum divides, the two daughter cells are not identical ; that in 

 fact the fundamental difference between soma and germ-cells begins at 

 this point. But this is precisely where many naturalists whose 

 observations are worthy of all respect difi'er from him. Weismann's 

 theory is tlierefore threatened at the very foundation. 



' A71, Examinatiun of Weismann, 1893, pp. 169, 170. 



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