CHROMOSOMES OF MOSQUITO 539 



these has divided, — c' . In other cases the division is so irregular 

 that it is impossible to determine the origin of the different 

 elements. This karyokinesis without cytokinesis occurs very 

 frequently in some individuals, not at all in others. When the 

 division of the tetrads is normal, we thus have a cell with twelve 

 chromosomes. 



A type of cell, rarely found by me, corresponds to the pycnotic 

 type of degeneration described by Lomen ('14). The nuclear 

 matter seems very much condensed and the cytoplasmic area is 

 very clear. These cells occur in various places in the testes of 

 a few individuals and usually near the walls. Figure 96 is a 

 drawing of two of these. 



Another type of degeneration mentioned by Lomen ('14) and 

 observed in my material is much more frequent than the pyc- 

 notic. In these cells the nuclei become very large and take a 

 blue-black stain with iron-haematoxylin. They seem to absorb 

 all the cytoplasm and to swell up to many times the size of the 

 original cells. Very dark masses may be seen in these nuclei. 

 Cells of this sort occur among the spermatogonia and they retain 

 their form without disintegration down among the spermatids. 

 They are more frequent in some individuals and do not occur 

 at all in others. Figure 97 shows such a cell accompanied by a 

 first spermatocyte nucleus lying alongside it and at a lower focus. 

 The difference in the size and the staining-reaction of the two is 

 very striking. The first spermatocyte shows its nucleolus con- 

 taining four darkly stained areas, as is usual. 



B. OVARIAN MITOSES 



The ovogonial chromosomes appear in all essentials like the 

 spermatogonial. Likewise the mitoses of the follicular cells of 

 the ovary are not essentially different. Late prophases show 

 three pairs, (figs. 98 and 99) one pair, b, smaller than the other 

 two, a and c. One of the larger pairs, c, frequently shows two 

 granules at one end. These may be comparable to the terminal 

 granules of spermatogenesis or they may be sex elements. They 

 are somewhat larger than the terminal granules usually are, but 



