APPENDIX I: 



ON GERM-PLASM. 



As already stated in the text (p. 71), Weismann's general 

 reasoning in support of his own theory of germ-plasm, as 

 against Darwin's theory of gemmules in any form, admits 

 of being reduced to arguments in favour of three proposi- 

 tions — viz., first, that there is no evidence of the transmission 

 of somatogenetic characters ; secondly, that the theory of pan- 

 genesis, which seeks to explain their supposed transmission, 

 is " inconceivable " ; and, thirdly, that its logical antithesis — 

 the theory of germ-plasm — is so much less beset with 

 difficulties, that by comparison it is simple, self-coherent, 

 and offers a real, as distinguished Irom a " formal," ex- 

 planation of the facts of heredity. 



The first of these propositions will be discussed at con- 

 siderable length in my next volume. The second and third 

 propositions, however, may be dealt with here. 



The following paragraph, which I shall quote sentence 

 by sentence, sets forth the grounds on which Weismann bases 

 the second proposition, namely, that any theory belonging 

 to the order of pangenesis — i. e., which supposes the carriers 

 of heredity ever to travel centripetally — is, from its very 

 nature, inconceivable. 



At first sight this hypothesis seems to be quite reasonable. 

 It is not only conceivable that particles might proceed from the 

 somatic to the reproductive cells, but the very nutrition of the 



