Q74 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, 
E 
Fic. 75.— Chromosomesinman. 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. 
