Various Opinions on Heredity. 117 



generation of medusae with no hydra stage. We should 

 then have a case of alternation like that which is pre- 

 sented by ordinary hydro-medusre. 



Summary of Chapter. 



A careful review of the reasons which have induced 

 various authors to believe that either sexual element may 

 transmit any characteristic whatever, leads to the con- 

 clusion that its truth is not proven. 



It is impossible to prove it by the phenomena of cross- 

 ing, since the only animals which can be made to cross 

 are essentially alike, and differ only in minor points. 



The homology between the ovum and the male cell is 

 no reason for supposing that their functions are similar, 

 and the differences between them should lead us to be- 

 lieve that their functions are not alike. 



There is no reason for assuming that each sex trans- 

 mits its entire organization to the offspring, in order to 

 account for the latent transmission of secondary sexual 

 characteristics, since this transmission can be more sim- 

 ply explained by assuming that each embryo inherits but 

 does not necessarily develop all the characteristics of its 

 species. 



Reversion and alternation of generations admit of a 

 similar explanation. 



iWc may therefore conclude that there is and can be 

 no proof that each sexual element transmits all the char- 

 acteristics of the parent, and that there is no a priori 

 absurdity in the hypothesis that the male and female 

 reproductive elements are unlike in function, and are 

 specialized in different directions. 



AVe can therefore enter without prejudice into an ex- 

 amination of the evidence for this latter view. 



