II CLEAVAGE 57 



The ratios given are for a temperature of 10, but the same 

 diminution with a slight rise at the end occurs at the higher 

 temperatures. The final values reached are practically the 

 same at all temperatures, and this suggests some causal rela- 

 tion between the amount of chromatin and the size of the 

 nucleus and cell. The ratio of plasma to nucleus diminishes, 

 as originally suggested by Boveri, but not at anything like 

 the rate which a growth of the nucleus to its original size 

 after each division would involve. At a low temperature this 

 ratio reaches a lower value, that is the nucleus is relatively 

 larger than at a high temperature. This is in accordance 

 with a rule which the studies of R. Hertwig and his pupils 

 on Protozoa seem to have established. 



Lastly, the ratio of the surface-area of the nucleus to the 

 chromosome volume does not remain constant, but diminishes 



and increases again. 



TABLE IX. 



As we have already seen, the nuclear surface diminishes as 

 development proceeds, though of course not as fast as the 

 nuclear volume. The nuclear surface, therefore, is determined 

 neither by the number nor by the volume of the chromosomes 

 taken alone. 



This, however, does not necessarily invalidate Boveri's state- 

 ment, which was based on a comparison of nuclear surfaces at 

 corresponding stages with a varying number of chromosomes, 

 not on a comparison of successive stages with the same number 

 of chromosomes. 



In the studies just considered the plasma whose volume is 

 determined includes the yolk-granules as well as the actual 

 living cytoplasm. It is the great merit of Conklin to have 

 attempted to measure the volume of the cytoplasm as distinct 

 from the yolk, at successive stages, and in the different cells. 



