48 



HEREDITY AND SEX 



In this case all of the spermatozoa (EE') contain 

 eight chromosomes. There is no visible difference 

 between them. Nevertheless, there is reason for be- 

 lieving that here also there are two kinds of sperm. 

 The principal reason is that there are all connecting 

 stages between forms in which there is an unequal pair, 



^scares S 



hi 



i» 



Fig. 27. 



jET^ 



as in lygseus, and forms with an equal pair, as in oncopel- 

 tus. Another reason is that the two sex chromosomes 

 behave during the synapsis stages as do the X Y chromo- 

 somes in related species. Moreover, the experimental 

 evidence, of which I shall speak later, leads us to con- 

 clude that the determination of sex is not due only to 



