MATURATION. 



27 



for black. These units will separate during the maturation of the germ cells, 

 and the resulting spermatozoa and ova will again recover the pure paternal or 

 maternal units. 



Sex Determination. 



In the great bulk of cytological and experimental studies of recent years 

 there is abundant evidence for the belief that certain chromosomes play an 



FIG. 17. Stages in the spermatogenesis of a grasshopper (Stenobothrus viridulus). Meek, i, 

 Spermatogonium in process of division, having 17 chromosomes (8 pairs and one odd). 2, Repre- 

 senting growth period of spermatogonium. 3-6, Division of the primary spermatocytes sixteen of 

 the chromosomes are paired while the "accessory" has no mate and passes as a whole to one of the 

 two secondary spermatocytes. 7-8, Division of the secondary spermatocyte with the odd chromo- 

 some, the latter splitting and giving one-half to each resulting spennatid. x, "Accessory" chromo- 



some. 



important part in the determination of sex. In the grasshopper (Stenobothrus 

 viridulus) the somatic number of chromosomes in the male is seventeen and in 

 the female eighteen. Owing to the odd number there is an unusual complica- 

 tion in the maturation of the male germ cell. When synapsis occurs eight pairs 



