458 



Fig. la. 



Fig. 16. 



quite different from the relations in the spermatocytic divisions. In 

 the metaphase a synaptic phase of the chromatin occurs before the 



latter resumes the usual arrangement 

 characteristic for the resting cell. In the 

 growth period the spermatogonia be- 

 come considerably larger, and show 

 yolk (?) globules in the cytoplasm. 

 Within the nucleus at this period are 

 two nucleoli, the one peripheral and 

 corresponding to the true nucleolus of somatic cells, the other more 

 central, larger and staining like the chromatin. 



In the prophase of the 1st spermatocyte the chromatin gradually 

 becomes arranged into the form of a single, thick, winding thread 

 (spirem). At no stage is there any evidence of longitudinal division 

 of this thread. The latter then breaks, by transverse division, into 3 

 or 4 large portions (figs. 2, 3), which are irregular in size and form, 

 and only rarely appear ring-shaped; and in the latter cases the rings 

 are clearly seen to be each composed by a single thread, with its ends 

 in mutual contact. These larger thread-fragments then divide trans- 

 versely until 7 elongate chromosomes are produced (fig. 4). These 

 chromosomes appear in the reduced number, and hence are bivalent. 

 Of importance is the fact that they appear transversely constricted 

 (fig. 4) before they become arranged in the equatorial plane of the 



Fig. 2. 



Fig. 3. 



Fig. 4. 



Fig. 5a. 



Fig. 56. 



spindle; and usually, also, this constriction is apparent on them before 

 they are segmented off from the spirem thread (fig. 3). The 7 chromo- 

 somes then become arranged in the equatorial plane of the spindle 

 (figs. 5a, e, 5Z», pole view), with their long diameter perpendicular to 

 this plane. Thoy then, at the commencement of the dyaster (fig. 6) , 

 divide transversely at the point where the constriction was already 

 present, and 7 halves wander to one pole, 7 halves to the other. 



In the preceding, more than in subsequent divisions, the chromo- 

 somes are seen to be of irregular size in the same nucleus. 



Towards the end of the dyaster stage of the 1st spermatocyte (fig. 7a; 



