Appendix I. 185 



continuity 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 



