Balls.—The Mechanism of Nuclear Division . 663 
Achromatic substances. 
Loosely divided into c oxy-chromatin ’ and ‘ linin Oxy-chromatin is 
closely related to chromatin, but its synthesis from, or by, the linin can take 
place without the pre-existence of the f molecular basis ’ (of chromatin) 
necessary for the formation of chromatin. 
The linin is of simpler composition, but very unstable ; in consequence 
of this instability it has the power of movement. 
There cannot well be differentiation of the oxy-chromatin granules, so 
that we may regard the dilated linin of a plasmosome as the reservoir 
in which the chromatin molecules rest. Their emergence from this retreat 
is the sign for their segregation or duplication. 
Linin can pass back into the cytoplasm, as exemplified in the fading of 
inter-chromosome spindle fibres after division. It can also be reconstructed 
from the cytoplasm, as exemplified in the increased size of the synaptic 
mother-cell. It is closely related to cytoplasmic fibrillae, and may even be 
chemically identical with them, but it is morphologically distinct and dis¬ 
continuous from them ; the increase in bulk of either is probably due 
to direct synthesis from simpler, or even non-living, constituents of the 
cytoplasm. 
It is worthy of note that the regularity of distribution of achromatic 
substance is far greater in the reduction division than in the vegetative 
divisions. In the latter, a large plasmosome may be very unequally 
divided. 
It should be noted that the broken spindle fibres contain no oxy- 
chromatin granules, so that the latter are very evenly halved in the reduction 
division. 
The behaviour of the thread-rings in fertilization has yet to be investi¬ 
gated. If the rings do not unite immediately—as seems probable—it will 
be of interest to determine the stage at which this happens, and to ascertain 
what takes place in synapsis. 
The writer is inclined to regard the spireme stage, after the plasmosome 
has disappeared, as being the typical form of the nucleus. From this stage 
it departs towards the resting nucleus with chromatin aggregated in the 
plasmosome, or towards the differentiated chromosomes of the dividing 
nucleus. Any stage other than the close spireme might thus be regarded 
as an adaptation to some special requirement of the cell. The various 
chromosomes are likely to have definite places in this spireme, and to retain 
those places at each successive division ; such geographical localization is 
not, however, an inevitable outcome of the present hypothesis. In those 
cases of vegetative division where the plasmosome is slung in the centre of 
the thread-ring by linin bridles, we see that complete breaking of the 
anastomoses of the reticulum is by no means necessary for regular division. 
In this way the spireme may have been phylogenetically derived from 
Z z % 
