84 ETHEL NICHOLSON BROWNE 



described later. In figure 73, some of the chromosomes already 

 lie at the periphery while others are still being transformed from 

 balls into threads in the interior. From this process it seems 

 clear that the material of one particular chromosome may be 

 broken up into more or less isolated bodies, which later arrange 

 themselves and fuse together to give rise to a continuous struc- 

 ture. As the last chromosomes form, some of the substance of 

 the original karyosphere is left behind as a plasmasome. This 

 body must apparently be formed from material that was in the 

 balls which segregates out in the process of thread formation. 

 The plasmasome is not colorless as it is in N. insulata, but remains 

 dark even in well extracted preparations, probably owing to the 

 fact that some of the chromatin is left behind. The plasmasome 

 has a vesicular appearance and is frequently vacuolated. It 

 gradually decreases in size and disappears in the late prophase. 



C. Notonecta irrorata 



The earliest stage occurring in my material is represented in 

 figure 74. This shows the presence of a looped spireme on the 

 nuclear wall, more or less oriented toward the karyosphere. The 

 spireme gradually disappears as in the other two species, probably 

 giving rise to the flaky material in the nuclear cavity. The karyo- 

 sphere at this stage is distinctly vesicular. Just before the aster 

 forms, however, it breaks up into a mass of balls of an inconstant 

 number which form threads, very much as described for N. 

 undulata (figs. 75, 76, A, B). A plasmasome is formed during 

 this process which sometimes takes a heavy chromatin stain 

 (fig. 77), and sometimes appears grey and vacuolated; it gradually 

 decreases in size and disappears in the late prophase. 



D. Conclusions and comparisons 



A karyosphere is apparently present in the three species of 

 Notonecta which I have examined, throughout the entire history 

 of the spermatocytes. In the very early stages and in the later 

 stages, this is the only body in the nucleus that takes a deep 

 chromatin stain, but there is an intervening stage when a chro- 

 matic spireme is present. It would appear that the chromatic 



