ioo An Examination of Weismannism. 



Weismann's system by stating exactly the effect 

 produced on his theory of evolution by the foregoing 

 disproof of its fundamental postulate — the absolute 

 stability of germ-plasm. 



Clearly, in the first place., if germ-plasm has not 

 been absolutely stable " since the first origin of sexual 

 propagation,'"' the hereditary characters of germ- plasm 

 may have been modified any number of times, and 

 in always accumulating degrees. It matters not 

 whether the modifications have been due mainly to 

 external or to internal causes. It is enough to have 

 shown that modifications occur. For, it will be re- 

 membered, the doctrine of the absolute stability of 

 germ-plasm is. that inasmuch as the Ci molecular" 

 structure of germ-plasm cannot be affected either 

 from without or from within, the only source of 

 "hereditary individual variations" is to be found in 

 admixtures of germ-plasms taking place in sexual 

 fertilization. Slight " molecular " differences having 

 been originally impressed upon different masses of 

 germ-plasm when these were severally derived from 

 their unicellular sources, so unalterable has been the 

 stability of germ-plasm ever since, that these slight 

 "molecular" differences have never been in any 

 degree effaced ; and although in sexual unions they 

 have for untold ages been obliged to mix in ever- 

 varying proportions, they still continue — and ever 

 must continue — to assert themselves in each ontogeny. 

 Therefore, as Weismann himself formulates this 

 astonishing doctrine, — <s The origin of hereditary in- 

 dividual variations cannot indeed be found in the 

 higher organisms, the Metazoa and Metaphyta ; but 

 is to be sought for in the lowest — the unicellular 



