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, 0!, et al.).
In Notonecta, 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. ii, upper cell.)
In the resting stage (Fig. I), each nucleus is exactly similar to
the single ftucleus 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 twice as
many chromosomes present as the diploid number for the species.
Each chromosome of the spermatogonial or oögonial metaphase
is represented by two exactly similar chromosomes in these
binuclear plates, as may be seen 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
are 6 large, 4 small and 16 intermediatu sized chromosomes, in
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