56 EDWIN G. CONKLIN 
period leads to an increase in the size of the nucleoli. During 
the normal cleavage of Crepidula the ratio of the nuclear volume 
to the nucleolar volume varies from 220 :1 to 4.6 : 1. 
Centrosomes and spheres are proportional in size to the volume 
of the protoplasm in which they lhe; they are always larger in 
large cells than in small ones and hence they grow progressively 
smaller as cleavage advances. 
In general the volume of each of the nuclear constituents named 
is influenced by the volume of protoplasm of the cell, and by the 
length of the resting period. The protoplasm contributes sub- 
stances to the growth of each of these constituents, and the more 
abundant it is the larger they grow, provided the period of growth 
is the same in all cases. Where the growth peroid (interkinesis) 
is very long the nuclei becomes unusually large and may ulti- 
mately absorb the greater part of the protoplasm. 
6. Comparison of growth of chromatin with increase of chemical 
substances and processes during cleavage. Loeb in several import- 
ant papers has shown that the nucleus is the oxidizing center of 
the cell, and that the chromatin is chiefly concerned in bringing 
about oxidations. Warburg (’08) found the oxidative power of 
the egg to increase at a relatively slow rate during cleavage. 
More recently, in view o: the oft-repeated assertion that the chro- 
matin doubles at each division, Loeb (’09) concluded that the 
supposed growth of chromatin in geometric ratio indicates that 
nuclear synthesis is of the nature of an autokatalytic reaction. 
Masing (’10) has shown that in the eggs of Arbacea pustulosa the 
nucleinic acid in the fertilized but unsegmented egg is as great 
as in the ‘morula’ with 500 to 1000 cells. He concludes that, 
‘“the colossal increase of nuclear mass in the cleavage leads to no 
perceptible increase of nucleinic acid in the germ. A corollary 
of this must be that the total quantity of nucleinic acid necessary 
to build up the nuclear apparatus of the germ must be preformed 
in the protoplasm” (quoted *from Godlewski, ’11). Shackell 
(11) has reached a similar conclusion with regard to the nuclein 
content of the egg and blastula of Arbacea punctulata. ; 
The results of my observations as to the rate of the growth of 
chromatin is especially significant when compared with the work 
