CELL SIZE AND NUCLEAR SIZE 55 
only equal to that of the germinal vesicle, though the volume of 
the chromosomal plates has increased 250 per cent; in Styela 
the volume of all the nuclei of the 256-cell stage is 77 per cent 
less than that of the germinal vesicle, though the total chromoso- 
mal volume has increased many fold during this period. 
Linin is a nuclear constituent which is found also in the proto- 
plasm, and during cleavage it grows in quantity at about the 
same rate as the nuclear and protoplasmic materials as a whole. 
The polar parts of the spindle and the astral rays arise in the pro- 
toplasm outside the nucleus, while the equatorial portion of the 
spindle comes from the nucleus, as is shown with great clearness 
in the cleavage mitoses of ascidians. Correspondingly the size 
of the spindle is a resultant of the volume of the nucleus and of 
the protoplasm. 
Chromatin is more distinctively a nuclear substance than the 
nuclear sap or linin, though it undoubtedly grows at the expense 
of substance received from the protoplasm and in turn contributes 
material to the protoplasm. From the 2-cell to the 32-cell stage 
in Crepidula the growth, of the chromatin amounts to between 
6 per cent and 10 per cent for each division, and as the fluid con- 
tents of the nuclei do not increase during cleavage the nuclei 
become more chromatic in later stages than in earlier ones. 
Chromosomal material, as represented in the condensed chro- 
mosomal plates of the anaphase, increases in volume 248 per cent 
from the 2-cell to the 32-cell stages of Crepidula, or an average 
growth of about 8 per cent for each division. Individual chromo- 
somes grow smaller as cleavage advances, but this is due to the 
smaller size of the nuclei from which they come rather than to the 
cell generation to which they belong; nuclei of the same genera- 
tion which differ greatly in size produce chromosomes which differ 
in size, the larger nucleus producing larger chromosomes than the 
smaller one. 
In the blastomeres of Crepidula the size and number of nucleoli 
(plasmasomes) are influenced by the size of the nucleus and the 
length of the resting period. In most of the nuclei there are two 
nucleoli, but when the resting period is long, these fuse into a 
single one. In experiments, anything which prolongs the resting 
