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, 



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. (AB, from Guyer, 1910; CE, 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. 



