126 Artificial Parthenogenesis 



8. The fact that the egg of so high a form as the 

 frog can be made to develop into a perfect and normal 

 animal without a spermatozoon — although normally 

 the egg of this form does not develop unless a sperma- 

 tozoon enters — corroborates the idea expressed in 

 previous chapters that the egg is the future embryo 

 and animal ; and that the spermatozoon, aside from its 

 activating effect, only transmits Mendelian characters 

 to the egg. The question arises : Is it possible to cause 

 a spermatozoon to develop into an embryo? The idea 

 has been expressed that the egg was only the nutritive 

 medium on which the spermatozoon developed into 

 an embryo, but this idea has been rendered untenable 

 by the experiments on artificial parthenogenesis. Never- 

 theless the question whether or not the spermatozoon 

 can develop into an embryo on a suitable culture 

 medium remains, and it can only be decided by direct 

 experiments. It was shown by Boveri, Morgan, Delage, 

 Godlewski, and others, that if a spermatozoon enters 

 an enucleated egg or piece of egg it can develop into 

 an embryo, but since the cytoplasm of the egg is the 

 future embryo this experiment proves only that the 

 egg nucleus may be replaced by the sperm nucleus; 

 and also that the sperm nucleus carries into the egg 

 the substances which induce development.- Inciden- 

 tally these experiments on merogony also prove that 

 the mere mechanical tearing of the cortical layer, — 

 which must happen in the separation of the unfertilized 



