82 ETHEL NICHOLSON BROWNE 



pact masses, either isolated or continuous, embedded in a less 

 dense substance (fig. 56). In this condition the karyosphere 

 persists during the whole growth period. 



3. Dissolution of karyosphere. Just prior to the formation of 

 the aster, the karyosphere tends to assume a more definite out- 

 line appearing in lightly stained preparations as a more or less 

 spherical body in which darkly staining bodies are embedded. 

 Figure 57 is from the same slide as figure 58, the former being an 

 earlier stage. After the formation of the aster, the chromatin 

 masses leave the karyosphere as compact bodies, either irregular 

 in shape or threadhke (figs. 59-61). It is perfectly evident that 

 the karyosphere is breaking up into its two constituents; the 

 darkly staining chromatin bodies are passing out of the karyo- 

 sphere, leaving the less dense, paler material which becomes 

 rounded and now appears as a typical plasmasome. As the 

 masses leave the plasmasome, they quickly proceed to the 

 periphery of the nucleus where they take on the form of double 

 threads, as will be described later. In figure 60 the plasmasome 

 is entirely free of chromatin, staining a pale gray; some of the 

 chromosomes are seen along the nuclear margin. The mass of 

 chromatin that has just left the plasmasome, is the large chromo- 

 some, M, which has been mentioned previously as one element of 

 the compound chromosome typical for this species. The plas- 

 masome has usually one or several small vacuoles in the interior. 

 The body gradually decreases in size and disappears in the late 

 prophase. 



B. Notonecta undulata 



1. Formation of karyosphere. In the earliest spermatocyte, 

 a small karyosphere is present, and the rest of the nuclear cavity 

 is filled with a reticulum of linin (fig. 62). The reticulum in- 

 creases slightly in staining capacity and takes on the appearance 

 of a very thin spireme, often twisted in spirals; a leader is usually 

 to be seen running from the karyosphere (fig. 63). This is 

 undoubtedly the leptotene stage. The spireme becomes more* 

 hea^fIly staining and tends to contract to one side of the 

 nucleus; the threads are still very thin, and in some cases appear 



