THEORIES OF HEREDITY 109 



solution of the one depending absolutely upon the so- 

 lution of the other. On one hand there is the prob- 

 lem of .heredity, that is, the problem of the resem- 

 blance between parents and offspring, and of the 

 process by which the diffe rent characters are trans-^ 

 mitted; on the other hand there is the problem of em- 

 bryonic development. 



How can all the parts of a complex organism have 

 their origin in an apparently simple egg-cell? What 

 are the factors of ontogenetic differentiation? As 

 any theory offering a solution of the first problem 

 also offers a solution of the second, we will examine 

 both at the same time, laying special stress, however, 

 on the former problem. 



The various theories of generation and heredity 

 need not be reviewed here. The controversy between 

 spermatists and ovists, the theory once known as the 

 "evolutionist theory," a misnomer at the present day, 

 and according to which the whole individual was "pre- 

 formed" in the ovum or in the spermatozoon, gradu- 

 ally shed its sheath and developed, the opposite the- 

 ory of epigenesis, etc., etc., — these can only interest 

 us from an historical point of view. And yet there 

 is no absolute divorce between those superannuated 

 doctrines and modern ideas. Certain theories of 

 heredity, acceptable to modern scientists, reveal a 

 state of mind akin to that of the old evolutionists. 

 Weismann himself says that his doctrines would have 



