202 
Allen. — Nuclear Division in the 
phenomena connected with synapsis are remarkably uniform throughout 
the plant and animal kingdoms ; and though some of these phenomena, 
such as the behaviour of the nucleoles and the changes in the affinity of the 
nuclear membrane for stains, are difficult to account for at present, it is 
possible that they may ultimately be shown to have a very important 
relation to the transformations going on in the substance of the spirem. 
The Period of the Uniformly Distributed Spirem. 
There now occurs a set of simultaneous processes which affect 
the arrangement of the spirem thread and the position of the nucleus 
within the cell. The rearrangement of the spirem (Figs. 20, 21) is a further 
manifestation of the tendency, already noted during the latter part of the 
synaptic period, toward a loosening of the coils of the spirem and its more 
even distribution throughout the nuclear cavity. The thread is quite 
uniform in thickness, showing very regularly in triple-stained preparations 
the two rows of dark-staining granules, to which short fibres are attached. 
The effect is, in triple-stained material, to give to the thread a somewhat 
ragged look ; in material stained with haematoxylin this is much less 
apparent, owing to the lack of differentiation of the granules in question, 
and to the general failure of the fibres to take up the stain. In the latter 
mentioned preparations the outline of the thread appears irregularly wavy, 
but not ragged. The thread, as shown by cross sections, is practically 
cylindrical. The nuclear membrane stands out sharply. 
During the rearrangement of the thread, there occurs a change in the 
location of the nucleus as a whole, so that, instead of the position it has for 
some time maintained near one side or one end of the cell, it comes to be 
approximately central. The final result is such a symmetrical arrangement 
of the various parts of the cell as is shown in Fig. 22, PL VII. 
The nuclear thread is now very uniformly distributed throughout 
the whole nuclear cavity. Portions of it are in contact at many points 
with the nuclear membrane. The course of the thread may best be studied 
in sections cut thick enough to include the whole or the greater part 
of a nucleus, stained with iron-haematoxylin and washed out in such a way 
as to decolorize the cell wall and cytoplasm, leaving the intra-nuclear 
substances still black. Fig. 23 is from such a preparation twenty-four 
micra in thickness. Even at this thickness the most favourably situated 
nucleus will be sectioned in one or both of the cutting planes, but enough 
is left to give an adequate notion of the course of the thread. The free 
ends observable in the figure are all on one or the other of the cut surfaces, 
and I have never found a free end except at a cut surface, or at so short 
a distance from the surface as to be easily accounted for by a slight displace- 
ment in cutting. A section thirty micra thick includes some entirely uncut 
