314 Relation of Use and Disuse to Evolution 



Problem of Inheritance 



The difficulty of explaining how the characters of the 

 organism can be transmitted by the minute germ had led 

 to numerous theories, among them one by Darwin, who 

 supposed that tiny gemmules were produced by each kind of 

 organ or tissue cell and brought by the blood to the gonads, 

 where they were organized into the eggs or sperms. This 

 theory of pangenesis did not long receive serious considera- 

 tion, but represented a thought that might have helped Spen- 

 cer establish the theory of transmission of modifications by 

 providing it with a conceivable mechanism. 



Weismann's theory, supported by many facts as well 

 as by speculative argument, at once reopened the discussion of 

 the inheritance of the effects of use and disuse, and of other 

 environmental influences. Weismann himself cut off the tails 

 of rats, both male and female, for over twenty generations, in 

 the search for evidence of transmission. Facts regarding the 

 failure of mutilation and analogous modifications to reappear 

 were accumulated. These negative facts, however, were not 

 taken seriously by the Lamarckians. They were moreover 

 irrelevant, since the distinction between a mutilation or 

 imposed alteration and a modification resulting from the 

 organism's own activities may be valid and important. 

 Weismann and his followers could continue to challenge 

 their opponents to produce positive evidence, while relying 

 for their rejection of Lamarckism upon logic. It is incon- 

 ceivable, is the argument, that changes in the soma should 

 influence the germ as Lamarck's theory required. It must 

 be admitted that this kind of reasoning sounds very much 

 like the argument, modifications must be inherited, other- 

 wise we cannot imagine how evolution takes place. 



Ob]ections to Weismann's Position 



There are two serious objections to the absolute separa- 

 tion, in theory, between germ plasm and soma. There are 



