78 ETHEL NICHOLSON BROWNE 



IV. KARY0SPHERE2 



A. Notonecta insulata 



1. Formation of karyosphere. The growth stages of the pri- 

 mary spermatocyte are probably separated by a considerable 

 interval from the last spermatogonial telophase. In the earliest 

 spermatoc3^tes observed (fig. 41), the chromatin is massed in a 

 single large body, the karyosphere, and thin strands of linin are 

 scattered through the nucleus. The first change to take place is 

 the accumulation of chromatin on the linin threads (fig. 42). 

 Although the source of this chromatin cannot be definitely ascer- 

 tained, it seems most likely, from a study of many of these nuclei, 

 that it comes from the karyosphere following the course of the 

 linin strands and tending to aggregate at particular points. The 

 threads from the karj^osphere are more or less twisted, and show 

 a distinct radial arrangement. The tendency of the cliromatin 

 to aggregate in clumps becomes more marked until the nucleus 

 is filled with small chromatin masses connected with each other 

 and with the karyosphere by thin deeply staining strands (fig. 

 43). During this process the chromatin masses are frequently 

 approximated in pairs (figs. 42, 43). This fact suggests that the 

 masses represent chromosomes which are conjugating. Although 

 the evidence is not conclusive that synapsis takes place at this 

 time, the whole process of the formation of these chromatin masses 

 seems unintelligible otherwise. The number of the chromatin 

 masses varies considerably in nuclei of the same cyst; the maxi- 

 mum number is however greater than the reduced number of 

 chromosomes, although probably not as large as the somatic 

 number. This is easily accounted for on the assumption that the 

 pairing of different bodies takes place at different times, as seems 



^ The term 'karyosphere' is used in this paper in the sense in which Blackman 

 ('03) first used it to denote a structure consisting of chromatin and other sub- 

 stances, such as linin and karyolymph. It is thus a broader term than karyosome 

 or net-knot or chromosome-nucleolus which is usually applied to a mass of pure 

 chromatin. 'Karyosphere' is practically identical with Carney's 'nucleole-noyau,' 

 or miniature nucleus; it is however difficult to determine the presence of a mem- 

 brane as is required by his definition. Although it is impossible to tell at all 

 stages whether accessory material is present with the chromatin, the term karyo- 

 sphere will be used throughout the discussion. 



