CHKOMOSOMES OF HUMAN SPERMATOCYTES 7 



In a few instances two, apparcMitly the two accessory chromosomes, 

 were seen consiclcral)ly to ouo sick; of the main mass of chromosomes, 

 surrounded l)y a small clear coiu't of cytojilasm. Twelve chromosomes 

 appear for division in the prhnary spermatocyte, of which ten are evi- 

 dently bivalent and two accessories. The two accessory chromosomes 

 pass undivided to one pole of the spindle considerably in advance of 

 the other cliromosomes with the result that half of the daughter cells 

 in this division receive twelve, and half only ten univalent chromosomes 

 . The ten univalent chromosomes which passed to the one 

 secondary spermatocyte unit€ again in pairs, at least in the majority 

 of cases, to form five bivalent chromosomes which appear at the equator 

 of the spindle when the cell is ready for division. The division here 

 presumably is an equation and not a second reduction division, judg- 

 ing from the size, shape and general appearance of the resulting daugh- 

 ter chromosomes There is some slight evidence that the 



secondary spermatocytes may occasionally divide with these chromo- 

 somes in their original condition of univalence. Ten of the twelve 

 chromosomes which passed to the other pole of the spindle in the pri- 

 mary spermatocyte behave in precisely the same way The 



two accessory chromosomes come to the equator of the spindle in the 

 secondary spermatocyte with the five bivalent, thus making seven in 

 all. Each accessory now divides so that the resulting spermatids 

 each receive seven chromosomes; that is five bivalents plus two ac- 

 cessory, or the equivalent of twelve univalent chromosomes .... 

 Of the total number of spermatids, half have in all probabilit}^ received 

 ten and half twelve (10 plus 2) univalent chromosomes (pp. 230-231). 



Montgomery in 1912 based his study of human spermatogene- 

 sis in part on portions of the same material studied by Guyer 

 and in part on testes of another negro. In his paper he does 

 not figure sperm atogonial plates. In the late prophases of the 

 primary spermatocytes he found 12 chromosomes. "Ten of 

 these must be gemini or bivalent chromosomes judging by their 

 late history and by analogy with other species. . . . The 

 two remaining elements are the univalent allosomes, but in 

 these late prophases it is practically impossible to say which 

 two these are" (p. 5). It may be noted that Montgomery's 

 allosomes correspond to Guyer's accessory chromosomes (i.e., 

 XX) and to what I call the X and Y chromosomes. Montgom- 

 ery believed, how^ever, that there is considerable variation in the 

 distribution of the X and Y chromosomes. In his own words, 



We may now summarize the allosome behavior in the primary sper- 

 matocytes with respect to their distribution to the secondary sperma- 

 tocytes and from this infer their distribution to the spermatids, using 



