216 WHAT 18 LIFE 



cally within the ovary of the guinea-pig. "^^ Leo Loeb 

 expressed the opinion that his observations "make it 

 extremely probable that in a relatively large pro- 

 portion of mammalian animals a spontaneous par- 

 thenogenetic development of ova takes place at some 

 period during the life of the animal. "^^ But this of 

 course does not invalidate the statement that, strictly 

 speaking, parthenogenesis seems to be out of the 

 question among the higher organisms. And the 

 general statement still holds though parthenogenesis 

 has been caused in so high a form as the frog — by 

 merely puncturing the frog's egg (first by Guyer, 

 also by Jacques Loeb, and others) ; for normally the 

 egg of the frog develops only when a spermatozoon 

 enters. 



As Jacques Loeb observed: "The reader knows 

 that the eggs of the overwhelming majority of 

 animals cannot develop unless a spermatozoon enters 

 them."" 



The differentiation of sex begins near the bottom 

 of the scale of life. However, examples of inter- 

 sexuality, that is, "the occurrence of examples inter- 

 mediate between the normal male and female of the 

 species" are cited from invertebrates (Dr. R. de la 



" Journal of Medical Research, 1901. 



'* Proceedings of the American Philosophical Society, Philadelphia, 1911. 



*" The Mechanistic Conception of Life, 200. 



