History of the Theory of Heredity. 77 



duce from two essentially similar eggs adult animals 

 which are so essentially dissimilar. We cannot attribute 

 this result to natural selection, for this law can only 

 act on successive individuals; we cannot attribute it to 

 the direct action of external conditions, for we know 

 that eggs may give rise to very different animals when 

 placed under identical surrounding conditions. Haeck- 

 el's statement that heredity is memory, contains a pro- 

 lound truth, as we have already seen, but it does not 

 help us to understand heredity. 



"We know memory only in connection with organiza- 

 tion, and if we believe that an egg contains the memory 

 of all the past experience of the race, we must believe 

 that it contains a complex organization to correspond to 

 the complexity of this past experience. 



So far as Haeckel's hypothesis of perigenesis has any 

 claim to be considered an explanation of heredity, it is 

 an hypothesis of evolution, not of epigenesis. 



Jager's view that the ovum is at first unspecialized, 

 and that it gradually assimilates from its developing 

 parent all the specializations of the structure of the lat- 

 ter, fails to account for reversion or for the transmis- 

 sion of adult characters by immature parents, and the 

 author is compelled to substitute for it an evolution 

 hypothesis when he comes to treat of reversion. 



There is no escape from the conclusion that the ovum 

 of an animal actually contains in some form the poten- 

 tiality of that particular animal, and Huxley acknowl- 

 edges that the development of an egg is in essence a 

 process of evolution. 



We thus find ourselves driven back from the modern 

 hypothesis of epigenesis to the long abandoned hypoth- 

 esis of evolution, and we must therefore inquire-whether 

 our recent great advances in knowledge of the forces 



