274 GERM-CELL CYCLE IN ANIMALS 



The above illustrations indicate that there is some 

 internal mechanism which controls sex, and that 

 certain chromosomes are, in at least many cases. 





.^:^ijfe. 





Fig. 75. — Chromosomes in man. A. First spermatocyte division show- 

 ing two accessories passing early to one pole. B. Two contiguous 

 spermatids, one without and the other with two accessories. C. Two 

 secondary spermatocytes ; the one above with an accessory. D. Sec- 

 ond spermatocyte with twenty-four dyads. E. Second spermatocyte 

 with twenty- three dyads. (A-B, from Guyer, 1910; C-E, from 

 Winiwarter, 1912.) 



factors in sex-determination. Several hypotheses 

 have been suggested as to the relation of these 

 chromosomes to sex, such as that sex is determined 

 by the quantity of chromatin present in the zygote. 



