302 L. J. BACHHUBER. 



(Fig. 23), usually close together. It may be that this position 

 is constant, but the massing of the chromosomes hides the 

 accessories (Fig. 24). In the division, the X and Y chromosomes 

 move towards the poles long before the division of the ordinary 

 bivalents (Figs. 25-29). The X is thus drawn to one pole, the 

 Y toward the other. In this manner, each of the secondary 

 spermatocytes will contain only eleven chromosomes, ten ordi- 

 nary and one accessory (Fig. 30). The ordinary chromosomes, 

 in their bivalent condition, are approximately twice the size of 

 the spermatogonial chromosomes. 



The split in the bivalent chromosomes is rarely in evidence 

 except immediately preceding the division, although in a few 

 isolated cases a V-shape becomes noticeable. 



When the chromosomes reach the pole the chromatoid body 

 seems to acquire more activity. During the formation of the 

 equatorial plate, this body migrates close to the densely crowded 

 chromosomes (Figs. 24-27). As soon as these start moving 

 toward the poles, the X and Y preceding, the chromatoid body 

 moves in between the two sets of chromosomes, lying approxi- 

 mately midway between the two centrosomes (Fig. 31). Just 

 before the new cell wall is formed, this body moves into the 

 cytoplasm of one of the newly formed spermatocytes. The 

 possibility presents itself that the chromatoid body always 

 follows either the X or the Y elements. The two accessories are, 

 however, so closely related in size that it has been impossible to 

 determine whether there is any such specific association. 



Occasionally, in the division of the primary spermatocytes, 

 there is found evidence that the accessory elements undergo a 

 precocious division. The accessories lie in the plane of division 

 and under certain conditions, they divide, forming two X and 

 two Y elements. The division then proceeds in the regular 

 manner with this exception: two X and two Y chromosomes 

 go toward the poles, again preceding the division of the ten 

 ordinary chromosomes (Figs. 32, 33). 



5. SECONDARY SPERMATOCYTES. 



The division of the secondary spermatocytes proceeds without 

 any appreciable rest stage. In the telophases of the preceding 



