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TEXT-BOOK OF EMBRYOLOGY. 



bothrus viridulus) the somatic number of chromosomes in the male is seven- 

 teen and in the female eighteen. Owing to the odd number there is an 

 unusual complication in the maturation of the male germ cell. When 

 synapsis occurs eight pairs of chromosomes are formed but the odd chromo- 

 some, which can usually be distinguished by its appearance, is left without a 

 mate (Fig. 13, 4). At the first maturation division this univalent chromo- 



FIG. 13. 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, Representing growth period of spermatogonium. 3-6, Division of the primary sperma- 

 tocytes 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 second- 

 ary spermatocyte with the odd chromosome, the latter splitting and giving one-half to 

 each resulting spermatid. x, "Accessory" chromosome. 



some does not divide but passes as a whole to one of the resulting cells, thus 

 giving two kinds of secondary spermatocytes (Fig. 13, 5). When the 

 secondary spermatocytes divide, however, the odd chromosome in one of 



