Nature of Sexual Diversity 139 



alike, not structures that are characteristically diverse. 4 

 The theory of two essentially diverse substances, male and 

 female, cannot be applied in any form to the mating of the 

 chromosomes. 



But if similarity between the parts that mate is the orig- 

 inal and elementary condition, how does it happen that in 

 other organisms, and indeed in most, we do find a diversity of 

 sex? Why do we find that as a rule in higher organisms a 

 small germ cell unites with a larger one? 



This has often been conceived as a special case of division 

 of labor. It is necessary for movement to take place in 

 order that union shall occur ; it is also necessary that there 

 shall be a certain amount of food or stored up energy for 

 the beginning of development in the new organism. Hence 

 it appears conceivable that variations should arise among 

 the originally equivalent cells, such that one set would 

 become more active, while the other would store up more 

 food. This of course could not occur without a correspond- 

 ing change in the underlying chemical processes, but the 

 difference in sex would according to this view not be coex- 

 tensive with life. It would be a difference that has arisen 

 in evolution, just as the difference between two races of 

 Difflugia has arisen. In Paramecium and related organisms, 

 according to this view, the difference has not arisen. 



What chiefly raise doubt as to the correctness of this idea 

 are the cases in which there is a physiological sex diversity 

 where no structural diversity can be seen. But there exist 



4 The chromosomes are structures that perpetuate themselves from 

 generation to generation, by division, as Protozoa do. It is not difficult 

 to so arrange breeding experiments that two offspring of the same 

 chromosome shall in a later generation be found in different sexes and 

 mate together, just as we may cause two offspring of the same Para- 

 mecium to breed together. This again would be difficult to reconcile 

 with the idea that the two mating chromosomes must be sexually di- 

 verse. 



