MITOTIC DIVISION OF BINUCLEATE CELLS. 



ETHEL BROWNE HARVEY. 



Attention has been called to the presence of binucleate cells 

 in the follicular epithelium of insects by several observers 

 (Korschelt, '87, Preusse, '95, De Bruyne, '97, Gross, 01, et al.). 

 In JVotonecta, binucleate cells are characteristic of the follicular 

 epithelium and also of the tissues lining the sperm duct and in- 

 vesting the spermatogonial cysts. These binucleate cells undergo 

 normal mitotic division, both nuclei being involved. As a 

 usual rule, both nuclei pass through the stages of division syn- 

 chronously, though rarely one finds one nucleus in advance of 

 the other. (Fig. i i , upper cell.) 



In the resting stage (Fig. i), each nucleus is exactly similar to 

 the single nucleus of a spermatogonial or oogonial cell, a con- 

 spicuous karyosphere being present (Browne, '13). In the pro- 

 phase, the two nuclei remain distinct and thick chromatin strands 

 are present in each nucleus (Fig. 2, upper cell, Fig. 3). When 

 the nuclear wall breaks down in the late prophase (Fig. 4), the 

 two nuclei may undergo a certain amount of fusion, or they may 

 remain entirely distinct and this is true also of the metaphase. 

 In some cases, two distinct plates may be seen in polar view 

 (Fig- 5) or two distinct spindles in side view (Fig. 6) ; in fact, 

 the two spindles may be so independent as to lie in different 

 planes, so that one is seen in side view and the other in polar 

 view (Fig, 7). In other cases, the two spindles become so in- 

 timately combined as to appear as one giant spindle. In polar 

 view a perfect equatorial plate is seen, but there are ticicc as 

 many chromosomes present as the diploid number for the species. 

 Karh chromosome of the spermatogonial or ooyonial metaphase 

 is represented by two exactly similar chromosomes in these 

 binuclear plates, as may be sern by comparing Fig. 8 from an 

 oogonial cell of Notonecta indica, with Fig. 2 (lower cell) from 

 a follicle cell of the same species. In the oogonial cell, there 

 ') large, 4 small and iO intermediate sized chromosomes, in 



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