1911.] Gametogenesis of the Gall-Fly, N. lenticularis. 479 
of these the reduced number is so clear as to leave no doubt, while in a 
number of eggs of the diploid series the absence of polar chromosomes, even 
at a stage when there are only two segmentation nuclei, is equally certain. 
This will become clearer in the detailed account of the maturation and 
segmentation stages which follows. 
In eggs belonging to both diploid and haploid series the early stages are 
alike. The nucleus appears as a rather small oval body, deeply and evenly 
stained, usually about half-way between the free end of the egg and the base 
of the stalk, either in the centre of the egg or nearer one side (Plate 17, fig. 1). 
It then approaches one side of the egg, at first with its long axis perpendicular 
to the egg-membrane, but as it reaches the edge it becomes round and finally 
flattened against the edge (figs. 2,3). The nucleus then swells, and becomes 
an oval vesicle lying close to the edge with its long axis parallel to it, and an 
irregular spireme or network of chromatin bodies is now visible within it 
(figs. 4, 5). From this stage onward the behaviour of the nucleus in eggs of 
the two types is different. In eggs of the diploid series the nucleus in 
prophase of division as just described sinks for a short distance into the 
egg, and forms a mitotic, figure parallel with the edge of the egg. I have 
only one egg in which the equatorial plate of this division is shown, and 
since it is lying sideways to the plane of the section the chromosomes cannot 
be counted accurately, but they are almost certainly more than ten. Several 
anaphase stages with the axis of the spindle parallel with the edge of the 
egg have been found: in one of these (fig. 6, a, 0), in which the figure is cut 
in face in two successive sections, in one section 10 chromosomes are visible, 
while at the other a larger number appears, but it is not clear how many are 
cut so as to appear in both sections. Many cases have been found in which 
the first division is just completed, and two vesicular nuclei occur, both near 
the edge of the egg and lying in a line parallel with it. At first the nuclei 
are near together and are quite small (fig. 7); later they enlarge and are 
found at a greater distance apart. In several such eggs the series of sections 
is quite complete, and no trace of polar chromosomes can be found. The 
next division of these two nuclei appears usually to be perpendicular to the 
edge of the egg, and may be seen to show considerably over 10 chromosomes, 
even if they cannot be counted with complete accuracy. In the later 
divisions the 20 chromosomes can usually be counted most easily in anaphase 
(fig. 8, cf fig. 46 of Part I of this paper); in some cases in prophase about 
20 irregular meridional chromatic bands can be counted in the nucleus before 
the membrane disappears (fig. 9). In some later prophases the intra-nuclear 
origin of the greater part of the spindle is seen (fig. 10). Sometimes in 
metaphase in eggs which are not very well fixed the chromosomes become 
2N 2 
