Weismanns theory of Heredity (1891). 71 



with under two heads— namely, indirect evidence as 

 derived from general reasoning, and direct evidence 

 derived from particular facts. 



The general reasoning is directed to show, (1) that 

 there is no evidence of the transmission of acquired 

 characters ; (2) that the theory of pangenesis is 

 " inconceivable " ; and, (3) that the alternative theory 

 of germ-plasm is amply conceivable. Now, to the 

 best of my judgement, not one of these propositions is 

 borne out by the general reasoning in question. But 

 as the latter is almost entirely of an a priori character, 

 and also of a somewhat abstruse construction, I think 

 the patience of any ordinary reader will be saved by 

 relegating this part of our subject to an Appendix. 

 Therefore, remarking only that any one who cares to 

 look at Appendix I ought, in my opinion, to perceive 

 that there is no real evidence against the transmission 

 of acquired characters to be derived from Weismann's 

 general reasoning in this connexion, I will at once 

 proceed to consider the evidence which he has 

 adduced in the way of particular facts. 



In the first place, as one result of his brilliant 

 researches on the Hydromcdusae, he has found that 

 the generative cells occur only in certain localized 

 situations, which, however, vary greatly in different 

 species, though they are always constant for the same 

 species. He has also found that the varying situations 

 in different species of the localized or generative areas 

 correspond, place for place, with successive stages in 

 a process of gradual transposition which has occurred 

 in the phylogeny of the Hydromedusae. Lastly, he 

 has found that in each ontogeny these successive 



