220 
Allen . — Nuclear Division in the 
and spreading apart of the spirem thread, which is now seen to be com- 
posed of segments (Figs. 94, 95), with their ends often close together or in 
contact, as though they had just broken apart from one another. Each 
segment has the shape of a V with its arms more or less curved. The 
angle of the V is on what was in the former division the polar side of 
the nucleus, and its free ends are on the side toward the partition-wall 
between the daughter- cells (the equatorial plane of the first division figure). 
Fig. 94 shows this arrangement of the V’s, the closed angles being on the 
upper side of the figure ; a few free ends are visible on the lower side. In 
some cases an end of one V lies directly over the end of a neighbouring V, 
and it is impossible to determine whether they are separate or attached. 
A comparison of Fig. 94 with Figs. 89 and 92 can leave no doubt, I think, 
that the V-shaped chromosomes which appear in the prophases of the 
second division are identical with the daughter chromosomes of the first 
division. Their arrangement is the same, except for the bending and 
curving due to their being gathered into the rounded cavity of the daughter 
nucleus. They are somewhat longer and thinner, a result of the elongation 
which, as has been mentioned, occurs after the formation of the daughter 
nucleus. The V-shaped chromosomes in Fig. 94 seem to be closed at their 
angles ; but certain of the V’s in Fig. 95, which gives a more oblique view 
of the nucleus than does Fig. 94, lie in such a way that it is evident that the 
two arms (the granddaughter chromosomes of the former division) are only 
in contact, but not fused, at the angle of the V. In the nucleus shown 
in Fig. 95, as in that of Fig. 94, there are twelve V’s. 
The nucleus continues to increase in size, becoming at the same time 
less flattened, so that it is, at the time of the disappearance of the nuclear 
membrane, nearly spherical. The chromosomes remain in the peripheral 
region, the central portion being occupied by nuclear sap. 
As the membrane breaks down and the cytoplasmic fibres enter 
the nuclear cavity (Fig. 96), the chromosomes are crowded into a close 
mass, as in the previous division. No material change has taken place 
in the appearance of the chromosomes since the segmentation of the 
spirem. When they are being pulled into place on the spindle it is often 
apparent that the two arms of each are really separate. Figs. 97-100 
represent individual chromosomes at this stage. The arms remain in con- 
tact at the end at which they were in contact in the anaphases of the 
previous division ; but at other points they may be variously in contact or 
divergent, resulting in figures which remind one of many of the various 
forms of the chromosomes of the first mitosis. They differ, however, from 
the heterotypic chromosomes in that there is never any twisting of the two 
parts about each other. 
Immediately after the disappearance of the nuclear membrane, as 
in the first division, the chromosomes lose the ragged fibres which have 
