4 EDWIN G. CONKLIN 
PART I 
CELL SIZE AND NUCLEAR SIZE IN NORMAL DEVELOPMENT 
I. Unequal cell divisions 
1. The maturation divisions. The most unequal of all cell 
divisions are those which give rise to the polar bodies. The 
actual diameter of the first polar body and of the egg, and the 
relative volumes of the two, are here given for a number of dif- 
ferent animals. These measurements were made on eggs which 
had been fixed, stained, and mounted in balsam. 
TABLE 1 
Sizes of polar bodies and eggs 
SPECIES oe anol Rees RELATIVE VOLUMES 
| 
Me Me 
Cumingia ‘tellincides. cs... eee 6 45 1 : 421.8 
Amphioxus lanceolatus................ 6 : 108 =| 1 : 5832.0 
Cynthia partitaw.-. A eee 9 | 105 | 1:1560.8 
Cerpidulasplande.=.2.- >). wae ee 12 | 136 1 : 1442.8 
Crepidulavfornicatase....{¢2 eee 12 | 182 1 : 3443.0 
Crepidulavconwexas can... ae 15 280 1 : 6434.8 
Crepidulayaduncay. s.r! el eee 15 | 410 1 : 20123 .6 
IDiUIIA DOORN AMOR, oi Ho mchaomed ehh ate alan cs oe. | 15 | 1600 iL SPA eis 0) 
In many other cases, such as the eggs of selachians, amphib- 
ians and birds, the disproportion between the polar body and the 
egg is much greater than in the cases here measured. The sig- 
nificant thing here is not merely the degree of inequality, but also 
the relative uniformity in size of the polar bodies as compared 
with the egg. Although the eggs of different animals vary enor- 
mously in size, the polar bodies vary relatively little, and it is 
safe to conclude, both from observation and experiment, that the 
polar bodies are in general the smallest cells which can be formed 
from egg cells by the process of normal cell division. 
In spite of this very great inequality of the daughter cells, the 
mitotic figure in the first maturation division of Crepidula and 
of many other animals is the largest in the whole life cycle. When 
