72 Heredity. 



analogy of the arrangements in plants to prevent self- 

 fertilization, we might expect to find some contrivance 

 both in animals and plants to prevent the ovum devel- 

 oping by itself without fertilization. ... On my hy- 

 pothesis the possibility of parthenogenesis, or at any 

 rate its frequency in arthropoda and rotifera, is possibly 

 due to the absence of polar cells" (Comp. Emb.., vol. i. 

 p. 63). 



The simplicity of this hypothesis renders it very fas- 

 cinating, but even if it were possible to accept it with- 

 out qualification, it would not affect our argument, for 

 it would still remain true that " the ovum is potentially 

 capable of developing, by itself, into a fresh individual," 

 and must therefore be very different in function from 

 the male cell, which under no circumstances exhibits a 

 similar power. 



My reasons for doubting the hypothesis are, first, that 

 a failure to discover polar cells in the eggs of rotifera 

 or of the arthropods may be due to the fact that they 

 are discharged very early in the history of the ovarian 

 ovum. We know that in some animals, as in hydra, 

 the polar cells are discharged while the egg is still con- 

 tained in the ovary, and we also know that the eggs of 

 many arthropods undergo in the ovary very peculiar 

 changes, which greatly obscure their fundamental simi- 

 larity to ordinary uncomplicated eggs, so that it is quite 

 possible that our failure to discover the polar cells may 

 be due to something else than to the fact that they are 

 never formed. The eggs of insects especially are very 

 peculiar, and "Weismann says that "nirgends im ganzcn 

 Thierreich die Ontogenese so verschoben und coeno- 

 genetisch entartet ist" as it is among the insects. This 

 author has figured, in the fertilized egg of a species of 

 Chironomus, certain bodies which are not present in the 



