2 I 2 
Allen . — Nuclear Division in the 
at definite points. The change is not in the outline of the chromosome 
itself, but in the attached fibrous material. It would seem that all of this 
material formerly present within the nucleus is made use of in the con- 
struction of the spindle. 
At the time of the disappearance of the nuclear membrane, the 
chromosomes have not, as a rule, shortened to their final form ; and, as 
in earlier stages, there is, between individual chromosomes, often con- 
siderable difference as to the amount of contraction that has occurred. 
The shortening is completed, however, by the time of their arrangement 
upon the equatorial plate (Figs. 56, 57). Even yet, as appears best in polar 
view (Fig. 57), there is a considerable diversity in their length, due for 
the most part to an actual difference in mass between individual chromo- 
somes ; and as to their arrangement on the spindle, their degree of 
curvature, and the relation to each other of the daughter segments, there 
is, as many writers have noted, a remarkable diversity. 
While the multipolar spindle is being transformed into the bipolar 
form the individual chromosomes become separated from the close mass 
in which they appear immediately after the collapse of the nuclear 
membrane. By the time of the formation of the ‘ multipolar diarch 5 figure 
the chromosomes are scattered irregularly along the whole length of the 
spindle. The majority of them lie with their long axes parallel, or nearly 
parallel, with the axis of the spindle ; and a chromosome so arranged 
is often seen to have a bundle of fibres attached at the end nearest the 
equatorial plane. Others lie transversely to the spindle. 
The chromosomes do not reach the equatorial plane at the same 
time ; and the separation into daughter chromosomes of those first arriving 
in this plane begins while the tardier ones are still scattered along the 
spindle. It is also not uncommon, before a chromosome has reached its 
position in the plate, to find its daughter segments diverging at one end 
toward the poles of the spindle, with a bundle of fibres connecting each 
diverging end with the corresponding pole. By the time of the completion 
of the plate, therefore (Fig. 56), it is a regular thing to find that the 
separation of some at least of the daughter chromosomes has already 
begun ; but the process of separation is for a time quite slow, even after 
the plate is fully formed. 
The chromosomes of the equatorial plate are arranged nearly in 
a single plane ; they seem to be somewhat crowded (Fig. 57), so that often 
one or more may be slightly above or below the plane of the rest. The 
apparent divergence from a single plane shown by the chromosomes in 
Fig. 56 is due in part to the fact that the plane of the section is not quite 
perpendicular to the equatorial plane of the spindle. 
The chromosomes still show much the same variations in shape that 
have been noted at earlier stages. Each chromosome is composed of two 
