44 EDWIN G. CONKLIN 
pared with that of the germinal vesicle; and even in the 256-cell 
stage the volume of all the nuclei is 77 per cent less than that of 
the germinal vesicle. Comparing the nuclear volumes of subse- 
quent stages with that of the germ nuclei, we find that up to the 
32-cell stage there is an increase of 826 per cent, or an average 
for the first 31 nuclear divisions of 26 per cent for each division; 
from the 32-cell stage to the 256-cell stage there is an increase of 
146 per cent, or an average increase of 0.6 per cent for each divi- 
sion. Since the germinal vesicle is unusually large and the germ 
nuclei unusually small, a better idea of the rate of nuclear growth 
in the egg will be obtained by comparing the nuclear volumes of 
later stages with that of the two cell stage, as was done in the case 
of Crepidula. Such a comparison is given in the last column of 
Coefficients in table 13. From this it appears that the nuclear 
growth from the 2-cell stage to the 32-cell stage is 290 per cent 
or an average increase for each of 30 divisions of 9.6 per cent; 
from the 32-cell stage to the 256-cell stage the nuclear volume in- 
creases 62 per cent, or an average increase for 224 divisions of 
0.27 per cent for each division. 
In the cleavage of the eggs of amphioxus and of echinoderms 
the rate of nuclear growth is essentially similar to that of the 
ascidians. Here also the germinal vesicle is very large and the 
total volume of the nuclei at the close of cleavage is much less 
than the volume of the germinal vesicle, though decidedly greater 
than the volume of the germ nuclei at the beginning of cleavage. 
In all of these cases the nuclei in the early cleavages contain little 
chromatin and much achromatin; while they are more densely 
chromatic in the later stages, showing that the chromatin has 
increased in quantity relatively more than the achromatin. This 
is probably due to the fact that the chromosomes take up less 
cytoplasmic substance in the smaller cells than in the larger ones, 
the amount of achromatin in the nucleus depending in large part 
upon the quantity of cytoplasm in the cell. 
4. Growth of different nuclear constituents. a. Nuclear sap. 
All of the substances within a nucleus do not increase at the same 
rate. The most abundant constituent of a fully formed nucleus 
is nuclear “sap, and this is scarcely present at all in the earliest 
stages of the nuclear cycle. During each resting period the nu- 
