14 J. E. WODSEDALEK. 



the pairing takes place by telo- or parasynapsis.) The whole 

 mass then moves toward the center (Fig. 22), the large clear area 

 in the nucleus disappears, and the nuclear wall becomes spherical 

 and clearly defined (Fig. 23). While the formation of the 

 spireme is going on, the cytoplasm, too, increases greatly in 

 volume and appears very granular. The cell now is fully twice 

 as large as a spermatogonium and judging by the large number 

 of cells that can be seen in the spireme stage one can safely 

 conclude that they remain in that condition for some time. The 

 spireme finally breaks up into U and variously shaped chromo- 

 somes (Fig. 25). The two large nucleoli, which remain in full 

 view throughout this stage, become oblong and can often be 

 seen close together (Fig. 25). 



3. Reduction Division. 



The primary spermatocytes when ready for division reveal 

 ten chromosomes in the late prophase or early metaphase stage. 

 The two accessories which are ordinarily off to one side (Figs. 8, 

 26, 27, and 29) can be recognized at a glance. The other chromo- 

 somes are usually arranged in a ring. Judging from their large 

 size and changed form, they are bivalent, representing the paired 

 univalent chromosomes of the spermatogonium. That is, of the 

 original eighteen chromosomes, sixteen have paired to form eight 

 bivalents of the primary spermatocyte and two have remained 

 unpaired as the accessory chromosomes. Sometimes, although 

 ten chromosomes can be counted, it is difficult to tell just which 

 are the accessories owing to overlapping. The chromosomes 

 differ somewhat in size as can be seen in Figs. 26 to 29. Figs. 

 9 to 12 and 30 to 37 show the accessories in characteristic posi- 

 tions in the metaphases of division of the primary spermatocyte. 

 They always pass entire, side by side and in advance of the 

 divided autosomes, toward one pole. This is possibly due to the 

 fact that they are not retarded by division. 



The fact that the chromosomes immediately after divergence 

 (Fig. 28) resume the appearance (except in size) that characterizes 

 the univalent spermatogonial chromosomes, and also because 

 the accessory chromosomes pass over entire to one pole in this 

 division while they are halved in the next division, seems to 

 indicate strongly that this is the reduction division. 



