CELL SIZE AND NUCLEAR SIZE 43 
cleavages is not so marked as in the gastropods, though of neces- 
sity the nuclei must grow smaller in all animals as cleavage 
progresses. 
In the ascidian, Styela (Cynthia) partita, the maximum 
nuclear diameters and volumes in the different cell generations 
are shown in table 12: 
TABLE 12 
Maximum nuclear diameters and volumes in Styela (Cynthia) partita 
COEFFICIENTS OF GROWTH 
Seen le ata | occas mn 
| Nuclear volume Dee 
be cubic Mb | 
Before first ma- 
turation.......| 54 824437 1) Poc0 
Before first | 
cleavage....... | 912+ 12 S09") 4\)) 0202 1.0 
Deelisnsee a 16u [ie EDISTO CONEY IN SDE 1.0 1.0 
Acellsn eee aan 14 (eee 74S:. | SO06s ame seley 1.34 
Sicelles eee cae: 13 fem O208 6° *| + OUTenn5 "Os 214 
Aocellase eae 11 TS! Oe Galan i260 
2 cellser Sue oe, ha vata) | 16,755 | 0.20 | 9.26 3.90 
GAicellsaen ee eee 8 In E52 |  OL20Pa ona 4.00 
ISicellsyyseees 6.5 18406. li .OL22eRtOntz 4.29 
256 cellsian see. 5.25 19,395 | Ob23 5 101,72 4.52 | 13.75 
The nuclei of different blastomeres of the same generation 
vary considerably in size, and I have not attempted to measure 
each individually, as in the case of Crepidula, nevertheless the 
measurements given represent approximately the average nuclear 
diameters for each generation of blastomeres. When the cells 
become very numerous a very slight error in the measurement 
makes a big difference in the results, and the total nuclear volume 
in the later stages may not be very accurate. Nevertheless the 
table does give a true idea of the order of magnitude of the nuclei 
in the different generations. 
In comparing this table with those for Crepidula it will be seen 
at once that the germinal vesicle is relatively larger, the germ 
nuclei smaller and the growth of the nuclear material in the 
early stages greater in Styela than in Crepidula. The volume of 
the egg and sperm nuclei represents a loss of 98 per cent as com- 
