CELL SIZE AND NUCLEAR SIZE on 
clear material as compared with protoplasmic may be prolonged 
beyond the period of segmentation (p. 167). But although he 
emphasizes the growth of the nuclear material as a whole during 
the cleavage, he specifically recognizes the fact that there is a 
rapid reduction in the size of individual nuclei in the early stages 
(pp. 174, 179). Hertwig (03) also has emphasized this great 
growth of the nuclear material during the early stages of develop- 
ment. He says (p. 116): 
There is an enormous disproportion of nucleus and protoplasm at the 
beginning of cleavage, and this disproportion is gradually equalized by 
the transformation of cell substance into nuclear substance. The man- 
ner of this may be imagined by supposing that resting protoplasm con- 
tains chromatin and achromatic material and that at every cell division 
it is analysed into these constituents serving for the growth of the 
nucleus. 
Loeb (09) also has called attention to the doubling of nuclei 
at each division, with the consequent increase of nuclear material 
in a geometric ratio, and the resemblance which this bears to 
autokatalytic reactions. 
The great increase in the nuclear substances during cleavage 
has been commented upon by many writers, and the references 
cited have been chosen rather because of the theories which have 
been based upon this phenomenon than because they represent 
an unusual opinion as to the phenomenon itself. At the time 
when the following computations of the rate of nuclear growth 
during cleavage were made, I was unaware that anyone had made 
computations of a similar sort. Since my material afforded an 
unusually good opportunity for making such computations, I 
carefully measured the diameters of the germinal vesicle, of the 
egg and sperm nuclei, of all the nuclei up to the 24-cell stage, of 
those of the 42-cell stage, and of the 70-cell stage,—every nucleus 
being measured at its maximum size, so far as possible,—with the 
results given in the following tables. These results have been 
as surprising to me as they are likely to be to any of my readers. 
After this work was completed I became acquainted with the 
work of Godlewski (08) and Frl. Erdmann (’08) on the sizes of 
nuclei and of individual chromosomes of the blastomeres of 
