CELL SIZE AND NUCLEAR SIZE ao 
unsegmented egg; however, in the blastula there is an actual loss, 
the total volume of plasma being about one-third less than in the 
unsegmented egg; during this period the nuclear material has 
increased in volume at the expense of the plasma. Whether the 
plasma actually increases during cleavage at the expense of the 
yolk has not been determined, so far as I am aware, in any case. 
By means of the centrifuge it is possible to throw the yolk out 
of the egg before cleavage and during the early cleavage stages, 
leaving the plasma which can then be readily measured. In 
later cleavage stages I have not been able to throw the yolk out 
of the small blastomeres by means of the centrifuge; but on the 
other hand the protoplasm and yolk are normally segregated in 
these stages so that it is possible to determine the approximate 
dimensions of both without having recourse to the centrifuge. 
The following table gives the total maximum volumes of all the 
nuclei, protoplasm and yolk in the eggs of Crepidula plana at 
various cleavage stages. Following Popoff (08), I have deter- 
mined the coefficients of growth of the nucleus and of the pro- 
toplasm for each stage; these coefficients are obtained by dividing 
the volume of a later stage by that of an earlier one, and they 
represent the growth in ‘times,’ or multiples of the initial quantity. 
In the first half of each column of coefficients the earlier’ stage is 
the one before maturation, while in the second half of each column 
it is the one before the first cleavage. The coefficient of growth of 
TABLE 8 
Total maximum volumes of nuclei, protoplasm and yolk in the eggs and cleavage 
stages of Crepidula plana 
| OTA COEFFICI- | COBFFICIENTS | TOTAL 
STAGE VOLUME OF} VOLUME OF |VOLUME OF VOLUME OF ENTS OF OF KERN- 
| NUCLEI PROTOPLASM YOLK NUCLEAR | PROTOPLASMC | PLASMA- 
| EGG GROWTH GROWTH RELATION 
| =I n 
| cubic w cubic cubic cubic 
Before ma- 
turation... 32,409 |  —-97, 131 1,625,460 | 1,755,000 | 1.0 1.0 1:3 
Before first, | 
cleavage... 21,375 | 121,430 1,346,105 | 1,488,910 |0.65/1.0 | 1.25 | 1.0 | 1:5.6 
2 cells...... | 14,476 123,482 1,100,700 | 1,238,658 | 0.45|0.67| 1.27 | 1.02| 1:8.5 
4 cells...... 23,100 154,280 969,468 | 1,146,848 | 0.71| 1.08] 1.58 | 1.27) 1:6.6 
S cells... ...2. | 25,144 164,136 972,320 | 1,161,600 | 0.77|1.17| 1.68 | 1.35) 1:6.5 
16 cells..... | 23,628 233,608 980,156 | 1,237,302 | 0.72) 1.10] 2.45 | 1.92] 1:9.8 
24 cells.....| 30,164 258,897 390,727 | 1,179,788 | 0.92] 1.41] 2.66 | 2.13) 1:8.6 
| ___ (231,000) (1,151,891) | | | (2.35) 11.90)! (1: 7.7) 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, No. | 
