210 
Allen.— Nuclear Division in the 
points, arise the many shapes described for the heterotypic division : I’s, 
J’s, X’s, Y’s, V’s, U’s, and O’s, as well as aberrant forms which are difficult 
of classification. 
As a rule, the daughter segments of any mother chromosome shorten 
and thicken at about the same rate; but this is not always the case. 
A marked instance of unequal shortening at an intermediate stage is shown 
in Fig. 35. The difference in length between chromosomes of the same 
nucleus or of different nuclei at about the same stage, due to variations 
in the rate of shortening, persists down to the time of spindle formation. 
When the chromosomes are being pulled into place on the equatorial plate 
some of them have attained nearly or quite their final form, while others 
are still comparatively long and slender. 
At the time of segmentation the distinction between chromatin and 
linin may still be detected in some cases, though I have not obtained any 
preparations of this or later stages in which this differentiation is as well 
marked as in some of the earlier figures. Shortly after segmentation there 
appear, in a few of my preparations, chromosomes in which the diffe- 
rentiation is fairly clear, and which show a double row of chromomeres 
in each daughter chromosome, an appearance already noted at this stage 
in the lily by Gregoire (’ 99 ) and Strasburger (’00), and in the pollen 
mother-cells of Naias by Guignard (’ 99 ), and interpreted by these authors 
as an early indication of the second longitudinal splitting. Miss Sargant 
(’ 96 , ’ 97 ) also finds a double row of c chromatin dots ’ in each daughter 
chromosome ; but her figures indicate that, as in the earlier stages, these 
dots are merely the external projections of the chromomeres. Fig. 31 
represents, on a larger scale, two chromosomes at the same stage as that 
of Fig. 30, in which appears this differentiation between chromatin and 
linin. A few short fibres are also seen attached to the chromomeres. 
It is not uncommon to find a slight forking of the ends of the daughter 
chromosomes (as at a, Fig. 31) ; and rarely there appears ( 5 , Fig. 31) 
a partial split in the interior of the daughter chromosome. There can 
be no doubt, I think, that the appearance of the two rows of chromomeres 
and the occasional partial fission of the daughter chromosomes really 
indicate the initiation of the second longitudinal split which is to be 
completed after the separation of the daughter chromosomes in the meta- 
phases. As the chromosomes shorten still further, the visible distinction 
between chromatin and linin entirely disappears, and with it all suggestion 
of a longitudinal fission of the daughter chromosomes. From this time 
on the substance of the chromosomes appears perfectly homogeneous. 
The fine fibres attached to the chromosomes remain visible, and the 
ragged appearance of the chromosomes increases with their shortening, 
partly from the crowding together of the points of attachment of the fibres, 
partly from a growth of the latter in length and thickness. There is thus 
