CHAPTER IX 



Weismann's Theory 



The two kinds of protoplasm; germ plasm. — Constitution of the 

 nucleus; ids, idants, determinants, biophors. — Ontogenetic 

 differentiation. — Disintegration of determinants; migra- 

 tion of biophors. — Continuity of the germ plasm. — Hered- 

 itary likeness. — Reserve determinants. 



WHAT has been called the Weismannian doc- 

 trine is an elaborate and inclusive set of re- 

 lated theories which constitute a well harmonised sys- 

 tem and which offer a solution for every one of the 

 main biological questions — heredity, variation, sexual 

 reproduction, adaptation, phylogenetic evolution, re- 

 generation, etc. The system was not created at one 

 stroke. For twenty years it grew gradually in Weis- 

 mann's mind, undergoing during that time many im- 

 portant modifications. 



For the definitive form of Weismann's doctrine we 

 must consult his "Evolution Theory" published in 1902 

 and which is, in his own words, a summary of all his 

 previous scientific works. Weismann accepts Nae- 

 geli's postulate as to two different kinds of protoplasm, 

 morphoplasm (Naegeli's nutritive plasm) and idio- 

 plasm. The former plays a rather subordinate part; 



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