CELL SIZE AND NUCLEAR SIZE 63 
PARA £1 
EXPERIMENTAL STUDY OF CELL SIZE AND NUCLEAR SIZE IN 
THE EGGS OF CREPIDULA PLANA 
I. Nuclear size and chromosome number 
In Crepidula the relation of nuclear size to chromosome number 
is the same as in the HEchinid larvae studied by Boveri (’05). 
By the use of various hypertonic salt solutions abnormal mitoses 
may be produced in Crepidula eggs; one of the most common 
of these abnormalities consists in the scattering of the chromo- 
somes, so that they do not fuse together to form two daughter 
nuclei, one in each cell, but many small nuclei. Indeed there 
may be almost as many small nuclei as there are chromosomes, 
every isolated chromosome being capable of producing a s° all 
nuclear vesicle. In all such cases the nuclear vesicles formed from 
a small number of chromosomes always remain smaller than 
those formed from a larger number. In any given species the 
size of the nucleus is proportional to the number of chromosomes 
which go into its formation, providing the other factors which 
control nuclear size, viz., quantity of cytoplasm and length of 
resting period, are the same. On the other hand the size of the 
cell body is not dependent upon the size of the nucleus inthe 
early cleavages of Crepidula, as Gerassimoff (’02) found to be the 
case in Spirogyra and as Boveri determined in the case of Echinid 
larvae, but the reverse is true. 
In the eggs of Crepidula which have been treated with salt 
solutions the cell body frequently does not divide at all and many 
nuclei may be left in a single cell; where the cell itself divides 
there is a tendency for the blastomeres to divide in normal fashion, 
giving rise to macromeres or micromeres as in the normal egg, 
even though polyasters and abnormal mitoses are present. Con- 
sequently these eggs afford no evidence that the size of the nucleus 
has an influence on the size of the cell body. 
