ECTOPLASM AND EVOLUTION 



determining that animals of a genus belong to the same 

 species is the capacity of normal fertilization and the pro- 

 duction of fertile offspring. As has been abundantly 

 shown, fertilization of an egg by a foreign spermatozoon is 

 only possible if the ectoplasm has been debased. The 

 unimpaired ectoplasm is a barrier to fertilization by non- 

 specific spermatozoa. Then species arose through changes 

 in the structure and behavior of the ectoplasm. 



In the differentiation of ectoplasm from the ground-sub- 

 stance we thus must seek the cause of evolution. 



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