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, 



FIG. 27. 



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 



