534 Lewis . — The Behaviour of the Chromosomes 
meres. However, this objection does not hold true for these genera. 
In sections in which the parts of the spirem are well stained differentially, 
the chromomeres are clearly observed in pairs, and this pairing is inter- 
preted as due to a longitudinal fission (Figs. 6 , 7). The formation of the 
spirem from the reticulum of the resting nucleus together with its con- 
tractions and recovery from synapsis and subsequent fission agrees closely 
with that given by Miss Ferguson ( , 04 ). 
In a short time the nuclear thread has completely disentangled itself 
and wound quite evenly throughout the entire cavity (Fig. 8). This figure 
is drawn from a section twelve microns thick. The free ends are seen 
to occur on the cut surfaces, and a study of this stage in preparations 
cut thick enough to include the entire nucleus has convinced me that there 
is present at this time an endless spirem. The spirem is quite jagged 
or granular in appearance, but when one observes closely the chromomeres 
the double nature is always revealed. 
The halves of the spirem now tend to diverge somewhat at intervals, 
but only in occasional nuclei do they ever become widely separated. The 
fission of the spirem was preceded by longitudinal fission of the chromo- 
meres, and this was evident at the time the skein loosened up from the 
synaptic ball. The longitudinal fission never becomes decidedly pro- 
nounced in either genus, in fact it might readily be overlooked entirely. 
Fig. 9 is drawn from the same loculus as Fig. 1 %. The majority of nuclei 
exhibit the structure of Fig. 9. These figures are typical of the spirem 
at this time. It has begun to stain much more uniformly than at the 
stages immediately following synapsis and the ragged nature is beginning 
to disappear. In place of such a structure a smooth homogeneous cord 
is formed (Figs. 10, 11). When one considers the extreme rareness with 
which nuclei are met with that reveal a divergence of the halves of the 
spirem, one is strongly inclined to disregard this as a normal step in the 
process of chromosome development. As the spirem shortens and thickens 
somewhat it becomes generally quite evenly distributed, and almost all 
evidence of longitudinal fission is lost. 
While these changes have been taking place in the chromatin, certain 
changes have gone on in the cell itself, which seem to be typical of this 
stage of mitosis and which may serve in a general way as an index of such 
stages. The cells during the resting period of the nucleus are packed 
together closely and are always polygonal in shape. The nucleus occupies 
a position near the central part of the cell. This position of the nucleus 
does not persist long, and gradually it tends to move toward one end of the 
cell. The cells begin to show signs of dissolution from each other by the 
time the synaptic mass has reached its state of greatest contraction, and 
when the nucleus has fully recovered the cells have rounded up and the 
tissue connexion has been lost. 
