CHROMOSOMES OF MOSQUITO 537 



The telophase nuclei become the interkinesis nuclei of the 

 second spermatocytes. 



d. Second spermatocytes 



1. Interkinesis, prophases, metaphases, anaphases, and telo- 

 phases. The young nucleus of the second spermatocyte appears 

 as shown in figure 76. The chromosomes are diffuse and are 

 connected with the two very dense nucleoli, one of which is 

 always larger than the other. The larger nucleolus becomes 

 diffuse (fig. 77) and disappears (fig. 78). Meanwhile the chromo- 

 somes thicken (fig. 79), and the smaller nucleolus, still densely 

 staining, appears attached to the end of a diffuse chromatic 

 thread. The small nucleolus then divides (fig. 80), as the 

 chromosomes become very thick. 



The separate pairs have not been clearly distinguished at this 

 stage, but it seems probable that the small nucleolus is descended 

 from the pair of terminal granules of spermatogonia and first 

 spermatocytes. Evidence for this is shown in figure 79, where 

 the small pair of chromosomes is separate from the other two 

 at the top of the figure. The small nucleolus is therefore asso- 

 ciated with the larger chromosomes. 



As the chromosomes become condensed, the small nucleolus 

 can no longer be distinguished and the three pairs appear as in 

 figure 81. The small pair in this and the succeeding figures is 

 lettered b. One member of pair a in figure 81 is foreshortened 

 as a result of twisting. In succeeding stages the middles of the 

 members of each pair touch and the ends radiate somewhat at 

 right angles (figs. 82, 83, 84, and 85). Thus three crosses are 

 formed which tend to occupy a peripheral position in the nucleus. 

 The monads do not cross each other, but merely touch, so that 

 the opposite arms of the cross are parts of different monads. 



Figures 83, 84, and 85 are from picro-formol-acetic fixation 

 and, as a result, the chromosomes are • somewhat distorted. 

 Figure 83 shows a trace of the nucleolus between the larger pairs. 

 It is surprising that this should persist so late in this cell as it 

 usually disappears before this time. The cross-shaped dyads 

 next group themselves into a metaphase, the ends of the monads 



