226 MICHAEL F. GUYER. 



Of the ordinary daughter chromosomes of this first spermato- 

 cytic division, a pair of small elongated ones not infrequently 

 are the first to emerge from the general equatorial mass as shown 

 in Fig. 7. One is led to suspect that they may possibly be compar- 

 able to the small pair of chromosomes found so constantly in cer- 

 tain of the Tracheata although the evidence is not sufficiently 

 decisive to make this an established fact. 



It is inferred that the division of the primary spermatocyte 

 is the reducing division, not simply because such a division ordi- 

 narily occurs at this stage, but from the fact that the chromo- 

 somes after divergence (Figs. 10, n) when compared with corre- 

 sponding divisions of the secondary spermatocytes are seen to 

 resume more the elongate, rod-like appearance that characterizes 

 the univalent spermatogonial chromosomes, and also because 

 the accessory chromosomes pass over entire to one pole here 

 while they are halved in the next division. 



It is evident from the foregoing that as regards chromatin con- 

 tent the result of the division of the primary spermatocyte is the 

 production of two dissimilar cells, one of which receives ten, the 

 other, twelve chromosomes. Fig. 10 is a drawing of one end of a 

 late anaphase of such a division showing twelve chromosomes (10 

 plus 2 accessory). Fig. n, in which only ten chromosomes are 

 visible, was drawn from what is probably the reverse end of a some- 

 what later anaphase than that shown in Fig. 10. It is just pos- 

 sible that it is a prophase of division in a secondary spermatocyte 

 where univalent chromosomes come to the equator, but if so it is 

 the exception rather than the rule, as the secondary spermatocytes 

 ordinarily divide according to a different scheme. In any event 

 the drawing serves to illustrate the fact that some daughter cells 

 of the primary spermatocytes have twelve chromosomes and some 

 only ten. 



In places both primary and secondary spermatocytes were found 

 dividing in the same field and one is led to conclude that either 

 there was no intervening period of rest between the two divisions 

 or that it was a very brief one. In other instances, however, un- 

 doubted resting stages of secondary spermatocyte nuclei were seen 

 in abundance. Approximately half of them showed, under 

 proper decolorization, two chromatin nucleoli of which one 

 was somewhat smaller than the other. 



