DIMORPHISM OF SPERMATOZOA 



623 



Yocum (7) has shown that the spermatozoa of the mouse are 

 cytologically dimorphic, one type having nineteen and the 

 other twenty chromosomes. I found this reflected in the 

 head lengths, as the following results show : 



It would thus appear that in three more species of mammals 

 the spermatozoa show dimorphism in the head length, while 

 in a fourth species, the cat, the evidence is uncertain. The 

 chief interest in these conclusions lies in the bearing which the 

 size dimorphism of the spermatozoa might have in determining 

 the proportion of the sexes at conception. If the potential^ 

 male and the potentially female-producing spermatozoa are 

 of different size, their activity and vigour may also be relatively 



