CHAPTER III. 



Weismann's theory of Heredity (1891). 



We now proceed to examine Weismann's theory of 

 germ-plasm, and as this in its various developments 

 has now become a highly complex theory, we had 

 best begin by marking out the lines on which the 

 examination will be conducted. 



As I have already pointed out. the Weismannian 

 system is not concerned only with the physiology 

 of reproduction : it is concerned also — and in an even 

 larger measure — with the doctrine of descent. The 

 theory of germ-plasm as a whole is very much more 

 than a theory of heredity ; it is a new theory of 

 evolution. The latter, indeed, is deduced from the 

 former; but although the two are thus intimately 

 related, they are nevertheless not mutually dependent. 

 For the relationship is such that the new theory of evo- 

 lution stands upon the basis supplied by the new theory 

 of heredity, and although it follows from this that 

 if the latter were disproved the former would collapse, 

 it does not follow that if the former were to be found 

 untenable the latter must necessarily be negatived. 

 Hence, for the sake of clearness, and also for the 

 sake of doing justice to both theories, we had best 

 deal with them separately. The present chapter, then, 



