MALE GERM CELLS IN NOTONECTA 85 



material comes from the karyosphere, and that later, at least 

 that part of it which contains the essential elements, returns to 

 the karyosphere. This flow of material back and forth from the 

 karyosphere seems highly remarkable, and is probably concerned 

 with a rearrangement of the chromatin particles, for which a 

 particular structure (i.e., the spireme) is necessary. It is unfor- 

 tunate that I have not been able to determine more definitely 

 how the definitive karyosphere is formed. In N. glauca, accord- 

 ing to Pantel and Sinety, a pale nucleolus is present in the early 

 stages and the chromatic material from the 'moniliform cords' 

 condenses around it, a process similar to that described for some 

 of the myriapods (Blackman '05 b, '07) and the dragon fly (McGill 

 '06). In other myriapods, the accessory chromosome is the cen- 

 ter around which the other chromosomes are deposited to form 

 the karyosphere (Blackman '05 a, '07, Medes '05). 



In Notonecta, the chromatin remains massed together in the 

 karyosphere, in an apparently inactive state during a long growth 

 period. It is usually possible at this time to distinguish the chro- 

 matin material as distinct bodies, not necessarily the individual 

 chromosomes, embedded in a less dense (plasmasome) material. 

 Such an intimate association of plasmasome and chromatin mate- 

 rial, where the latter is recognizable as distinct bodies, has been 

 described in some of the myriapods (Blackman, Medes), and in 

 the case of the A"F-chromosomes in some of the reduvioids 

 (Payne '09) and in certain Coleoptera and Diptera (Stevens). 

 In some cases, e.g., in Scolopendra heros (Blackman '05 a) and 

 in Hydrophilus (Arnold '08), there is apparently no plasmasome 

 material associated with the karyosphere. The distinction of 

 two sorts of material is extremely apparent in N. insulata in the 

 early prophase, when the chromatin leaves the karyosphere as 

 compact masses, and the remaining material becomes a typical 

 pale plasmasome. In N. irrorata and N. undulata, and appar- 

 ently also in N. glauca, the dissolution of the karyosphere takes 

 place a little differently, by breaking up at once into a number of^ 

 separate elements. In either case, there can be no doubt that 

 the material which forms the chromosomes comes from the karyo- 

 sphere. The events described for Notonecta do not seem to me 

 at variance with the hypothesis of the genetic continuity of the 



