38 EDWIN G. CONKLIN 
Echinus and Strongylocentrotus. Godlewsky found that from 
the 1-cell to the 64-cell stage the nuclear substance grows nearly 
in geometric ratio; from the 64-cell stage to the blastula, with 
about 1256 cells, there is little increase in the nuclear substance, 
but since he supposes that the number and size of the chromo- 
somes in the later stages remain the same as in the earlier ones, 
the nuclei must become richer in chromatin in the later stages. 
He finds that the volume of the plasma in the blastula stage is 
about one-third less than in the unsegmented egg and he con- 
siders that a large part of this lost plasma has been converted into 
chromatin. Erdmann (’08) has made a careful computation of 
the volume of the resting nuclei and of individual chromosomes 
in the early cleavage stages, and in the blastula and gastrula of 
Strongylocentrotus. She finds that the chromosomes of the 
pluteus period have only about one-fortieth the volume of those 
of the first spindle, but though the individual chromosomes grow 
smaller continually, the total nuclear volume increases at the 
expense of the plasma up to the late blastula stage. 
1. Nuclear growth during the cleavage of the egg of Crepidula. 
The maximum, minimum and mean volumes of the nuclei at 
different stages of the cleavage of Crepidula plana are given in 
tables 3 to 5 and the coefficients of growth of all the nuclei are 
given in table 8. It remains only to summarize the facts there 
presented and to give the nuclear volumes and the rate of growth 
in certain later stages of the cleavage. This has been done in 
table 9, where the maximum, miminum and mean nuclear vol- 
umes of every nucleus from the 2-cell to the 32-cell stage is given, 
together with the coefficient of growth for each stage. Since this 
table starts with the 2-cell stage the coefficients of growth are 
different from those given in table 8, where subsequent stages are 
compared with the germinal vesicle or with the germ nuclei. 
For the purpose of determining the usual rate of growth for each 
cycle of cell division during the cleavage it is desirable to start 
with the 2-cell stage. ‘The germinal vesicle is an extraordinarily 
large nucleus, and since two nuclei are present in the egg before 
the first cleavage the nuclear condition at this stage is unusual; 
on this account the rate of nuclear growth during cleavage is 
