SOMATIC MITOSES OF THE MOSQUITO 583 



P. F. A. No. 3 fixed material) only three threads with splits 

 occasionally appearing at the ends of the threads. It is easy to 

 understand how, unless the fluid reached the cell almost immedi- 

 ately, the delicate splits or lines of separation would be com- 

 pletely or partially obliterated. Such a case is shown in figure 

 1 where only three threads appear. It is very interesting to 

 note the orientation of the three pairs of chromatin threads in 

 the prophase. If the plates will be referred to it will be seen 

 that the apices of the three V's in each cell (the point of spindle 

 fiber attachment) are directed toward the same pole, suggesting 

 the position in which the chromosomes lie when last seen in 

 the anaphase. This condition is very suggestive from the point 

 of view of the individuality hypothesis. As the prophases 

 approach metaphase the paired chromatin threads seem to sepa- 

 rate and gradually lose the characteristic prophase orientation. 

 The beginning of this process is illustrated in figures 13 to 16. 



I am unable to acicount, at present, for the size variation 

 which occurs between the chromosomes of various cells. This 

 will be apparent chiefly in the drawings of the prophase figures. 

 Figure 7 is of an especially large cell. It will be noticed that the 

 size relationship between the chromosomes of the same cell is 

 apparently the same in all cases. 



Metaphase. When the arrangement of the prophase is com- 

 pletely lost, the threads have shortened and thickened, have 

 separated rather widely and the characteristic metaphase plate 

 stage appears, figures 17 to 24, 26 to 30. This stage Whiting 

 has designated as stage A. The chromosomes undergo another 

 rearrangement and the three pairs line up side by side prepara- 

 tory to division (Whiting's stage B), figures 25 and 31. A good 

 side view of the spindle with the chromosomes distinctly visible 

 is difficult to find but figures 32, 33 and 34 were drawn from 

 clear cells in which the plates were slightly tilted permitting the 

 six chromosomes on the spindle, each split preparatory to divi- 

 sion, to be seen. Spindle fibers are visible but their actual 

 attachment to the chromosomes is not evident. Judging from 

 the anaphase figures, however, (fig. 37a) it seems evident that 

 the fiber is attached to the apex of the V. 



