CHROMOSOMES OF HUMAN SPERMATOCYTES 11 



point since they do not show the plasmosome. Von Wini- 

 wartei''s ch^ini that this body is single, i.e., unpaired, I can not 

 confirm. 



This bipartite chromatin body seems to be an unequal pair 

 of idiochromosomes which can be traced from the telophase of 

 the last spermatogonial division through the rest stage to the 

 prophase of the primary spermatocyte (figs. 5, 6, 7, 8, 9 and 10). 

 In the prophases and in the later metaphases 12 presumably 

 bivalent chromosomes may be counted, counting the XY pair 

 as one. Guyer and Montgomery also find twelve chromosomes 

 at this time but they consider the X and Y as single univalent 

 chromosomes forming two of the twelve. 



I have already considered Guyer's and Montgomery's inter- 

 pretation of the distribution of the two idiochromosomes. I 

 too have found side views which support Guyer's vie.v that the 

 two (accessory chromosomes) pass undivided to one pole of the 

 primary spermatocyte spindle. I also find division figures 

 illustrating the various possibilities considered by Montgomery; 

 but I am inclined to believe that X and Y divide in this division 

 both from the undeniable evidence of side views (figs. 21, 22, 

 23 and 28) and, what seems to me is more important, from the 

 fact that I always found that daughter groups in anaphase 

 stages contain an equal number of chromosomes, namely 12, 

 counting the two parts of the divided XF as one (figs. 29 and 30). 

 It may be, of course, that an occasional variation in the distribu- 

 tion of this body does occur, but the evidence from my material 

 points to its division in the primary spermatocyte as the usual 

 method of distribution. It may be noted that Montgomery 

 also found this condition in a nmnber of cases (''Condition E"). 



I can confirm Montgomery and von Winiwarter in the pres- 

 ence of an interkinesis stage. The occurrence of chromatin 

 structures in the nucleus at this time comparable to the chroma- 

 tin nucleus of the primary spermatocyte also points to the divi- 

 sion of the XY in the first maturation mitosis. 



In the secondary spermatocyte division I find 12 chromosomes, 

 one of which in most cases can be identified as XY by its pe- 

 culiar shape. I have not been able to determine by direct ob- 



