3O J. E. WODSEDALEK. 



nucleoli are conspicuous and lacking in the others. In a few 

 cases, at least, there is no resting period in the secondary sper- 

 matocytes. A small centrosphere containing a relatively large 

 centrosome is present. 



15. During the metaphase of the secondary spermatocyte one 

 half show four large bivalent chromosomes, and the remaining 

 show the four large bivalents plus the two accessories or six 

 chromosomes. A second pairing has apparently taken place 

 but the division is simply equational as the four large chromo- 

 somes often manifest a quadrivalent character. The accessories 

 remain unpaired. 



1 6. The quadrivalent nature of the autosomes in the secondary 

 spermatocytes becomes all the more certain after division, as the 

 chromosomes passing to the poles are of the bivalent nature. 



17. The type of secondary spermatocyte which received eight 

 chromosomes after the first maturation division gives rise to two 

 spermatids each containing four bivalent or eight univalent 

 chromosomes. The other type which received ten chromosomes 

 after the first maturation division gives rise to two spermatids, 

 each containing four bivalent or eight univalent chromosomes 

 and the two accessories, each accessory having divided here for 

 the first time since the spermatogonial division. 



1 8. The dimorphic nature of the spermatids which develop 

 into spermatozoa is further evinced by the presence of the two 

 nucleoli in approximately half the cells. The centrosome is 

 again conspicuous. 



19. The first noticeable change in the transformation of the 

 spermatid is in the centrosome. It emerges from the small 

 sphere and divides into an anterior rod-shaped and a posterior 

 disc- or ring-shaped body. 



20. Both of the centrosomes contribute to the development of 

 the axial filament. A portion of the anterior one persists as the 

 end-knob, while the posterior body is finally cast off. 



21. A portion of the sphere migrates to the opposite side and 

 gives rise to the acrosome which disappears when the spermato- 

 zoan is fully developed. 



22. The nucleus of the spermatid passes to one side of the cell, 

 elongates and flattens and forms the head of the spermatozoan. 



