52 EDWIN G. CONKLIN 
together becoming fewer and larger as the individual chromosomal 
vesicles fuse. For a considerable period two nucleoli are com- 
monly found in each nucleus, one in each gonomere, or nuclear 
half. However, when the resting stage is long, these two fuse 
into a single large plasmasome. 
While the nucleus continues to grow in size up to the time of 
the dissolution of the nuclear membrane, the plasmasome usually 
disappears before the formation of the spireme. In comparing 
the relative sizes of nucleoli it is important to compare corre- 
sponding stages; accordingly in my measurements they were 
measured when they had reached approximately their maximum 
size, and before the nucleus had reached its maximum. Nucleoli 
differ more or less in size even in different cells of the same genera- 
tion, owing perhaps to the more or less complete fusion of the 
many original nucleoli; it is significant in this connection that 
after a long resting period they are much more uniform in size 
and constant in number than when the resting period is short. 
The following table gives the diameters of nuclei and nucleoli 
(plasmasomes) in various blastomeres of Crepidula: 
, TABLE 14 
Maximum nucleolar size and nuclear size in the blastomeres of Gini plana 
| DIAMETER | VOLUME NUMBER | DIAMETER VOLUME | NUCLEAR- 
STAGE BLASTOMERES Or | OF | OF OF | OF NUCLEOLAR 
| NUCLEUS NUCLEUS | NUCLEOLI | NUCLEOLI | NUCLEOLI RATIO 
ML cubic | : a cubic pL 
lcell,beforematuration 42 | 32,409 | 1 12 905.0 35:1 
ZcellayA By CD rants 20 4,189 2 3 28.0 | 149: 1 
A cells) Ass © 2D a5 ae. 15 1,767 | 2 25, 14 Meee 220) So 
Scalia PAID: al “19 3,091 | 2 3 | 28.0 | 128-3 1 
Haldar | lS. 1,150 | 2 Dales 7.0 | 164 :1 
2A-2D...5.:.) 14 1,437 2 2 S75) 180521 
12cells 2 } | 
Oy Ge sate bh \15 tener. 2 2 8.3 | 220:1 
Geechee Taide... 12 905 | 2 332 18.3 | 50 al! 
Lat-td? ees. 7 180 2 1 1.0 | 180 :1 
3A-3D.. ge 1,767 1 74 221'0)| S31 
20cells 2 2 | 2 
Car Nsesodam 15 1,767 | 2 3 28.0 63:1 
25 cells ric ea Pee | 9 382 | 1 3 14:0 | 2/7 
32 cells, 4a-4chs,-co5- 50 13 905 1 6 113.0 Sica 
Ca. 100 cells, 4A-4D.. 15 1,767 1 9 382.0 | 4.6 :1 
Fulgur carica: 
Ca. 1000 cells, 4A-4D_ 96 462,192 1 27 10306.0 | 44:1 
