244 MICHAEL F. GUYER. 



spectively received from the primary spermatocyte, a smaller 

 number, usually four (Figs. 175-183, photos 36, 37) or five (Figs. 

 161-163), appear at the equator of the new spindle. The groups 

 of four I interpret as characterizing those cells which received 

 only the eight ordinary chromosomes at the preceding division, 

 the groups of five, those which received the extra, curved element 

 in addition to the eight ordinary ones. This view is strengthened 

 by the fact that in the groups of five, the fifth element (Fig. 163) 

 may often be seen to resemble the original special element of 

 the primary spermatocyte. Furthermore, at the time of divi- 

 sion this element lags behind like a typical X-element and often 

 does not divide until the other chromosomes are well on their 

 way toward the poles of the spindle (Figs. 168, 172, 174, photo 63). 

 While my best preparations show groups of four and of five 

 respectively to be by far the prevailing type, it is not unusual to 

 find other cases in which the number may be six, or seven any 

 numerical combination, in fact, that can be made by the union in 

 twos of one or more pairs of chromosomes out of a total of eight. 

 The explanation seems to be that while pairing of the ordinary 

 chromosomes is the rule, this union is sometimes incomplete or 

 does not occur between certain individuals. In both the four 

 and five groups one of the chromosomes is smaller than the others 

 (Fig. 177) and where only one pair of the autosomes remains 

 unpaired in the secondary spermatocyte, it seems most frequently 

 to be the two components of this smaller bivalent one (Figs. 

 184 and 185). This gives five chromosomes without the X-like 

 one in what typically is a four-group, and six chromosomes in 

 what otherwise would have been a five-group where the curved 

 element is present. In early metaphase of the secondary sper- 

 matocytes a bipartite condition of the chromosomes preparing 

 to divide not infrequently reveals their double nature (Fig. 180). 

 Moreover, the chromosomes may tend to resolve into their 

 original univalent condition as they progress toward the poles 

 presumably after having divided as a four or five group (Figs. 

 1 68, 172). The occasional finding of groups of eight or nine 

 univalent chromosomes at one pole or the other in the telophase 

 of such a division indicates that the division is in no sense a 

 reduction division as was probably the preceding one. Fig. 164 



