104 Heredity. 



torv, both scales and feathers have had a common orio-in 

 in an epidermic structure, wliich has gradually become 

 specialized into' these organs. 



While the homology between the ovum and the male 

 cell is no reason for assuming that their functions are 

 now alike, the constant differences between them, 

 throughout almost all of the organic world, seem to 

 afford a very convincing reason for believing that their 

 functions have been specialized in two divergent direc- 

 tions. 



If we can show that good might have resulted to the 

 organism from such specialization, and from the restric- 

 tion of certain parts of the reproductive function to one 

 element, and the restriction of others to the other, w^e 

 may feel confident that, provided variations in these 

 directions have at any time arisen, natural selection 

 would have seized upon and perpetuated them. 



I hope to show the great usefulness of a specialization 

 of this sort, and if I can do so, it is clear that the known 

 differences between the ovum and the spermatozoon are 

 reasons for a belief in its existence, while the only con- 

 clusion which can be drawn from the homology between 

 them is, that at one time their functions were alike. 



Tlie Arguments from the Ti'mismission of Latent Sexual 

 Characteristics; from Reversion, and from Alterna- 

 tion of Generations. 



In addition to the reason given by Huxley for a belief 

 in the dual nature of each organism, he might have 

 adduced the fact that the characteristics of each sex are 

 potential and latent in the organism of the opposite sex, 

 as is proved by the transmission by a father to his daugh- 

 ter of characteristics inherited from his grandmother. 



The fact that the characteristics of one sex are latent 



