MALE GERM CELLS IN NOTONECTA 83 



to run parallel in pairs (fig. 64). This is probably a synizesis 

 stage and it is likely that a conjugation of the parallel threads 

 takes place, although this cannot be conclusively demonstrated. 

 In the next stage, the spireme is somewhat thicker and becomes 

 arranged in loops, oriented toward the karyosphere (fig. 65) . The 

 loops next become attached to the karyosphere at their apices; 

 this gives the appearance of arms radiating out from the karyo- 

 sphere (fig. 66), and affords an opportunity for the transfer of 

 material from the loops to the karyosphere. Very frequently 

 the threads give the appearance of being longitudinally spht. 

 The loops now recede from the karyosphere and become arranged 

 on the nuclear wall while the karyosphere remains in the in- 

 terior (fig. 67). The loops gradually disappear, and the nucleus 

 is filled with an irregular reticulum which is appreciable when 

 the staining is dark, but pale when the stain is more extracted, 

 in contrast to the dark karyosphere. 



The early history of N. undulata thus differs markedly from 

 that of N. insulata. There is no formation of scattered chro- 

 matin masses, but instead a leptotene stage which is followed by a 

 synizesis or contraction, after which a spireme is present which 

 is quite similar to that of N. insulata. The fate of the material 

 in the spireme offers the same difficulties as in N. insulata, but it 

 seems probable that here too some chromatin passes into the kary- 

 osphere, and other chromatin is segregated out and furnishes the 

 material in the nuclear cavity. 



2. Description and dissolution of karyosphere. The karyosphere 

 of N. undulata appears very much as it does in N. insulata; it 

 tends to be vesicular in the early stages, especially in darkly 

 stained preparations, but later appears granular or rope-like 

 (figs. 68, 69). At the approach of the prophase the karyosphere 

 becomes broken up into a variable number of small round bodies, 

 giving the appearance of a mass of marbles (fig. 70). The mass 

 loosens and from it project one or two longitudinally split threads 

 (figs. 71, 72). That the thread may be formed directly from 

 'the balls which become arranged in pairs is evident from figure 

 72. As the double threads form, they go to the nuclear wall where 

 they becorne the diffuse prophase chromosomes which will be 



