NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 311 



age to old age is due to decreases in both nuclear and cytosomal 

 volume, the percentage of cytosomal decrease being much the 

 greater. 



The variability of nuclear and cytosomal volumes, as indicated 

 by the standard deviation (o-), is perhaps worth noting. The 

 nuclear volumes are much more uniform in the early adults than 

 later, while the cytosomal volumes are more constant in middle 

 life. The probable errors pertaining to the values of the standard 

 deviation appear to show that this conclusion is well founded. 



Stomach-intestine. The relative volumes of the nuclei of the 

 cells in this organ are summarized as follows : 



Relative nuclear volume in stomach-intestine of young 



adult females 0.071 ± 0.003 



In middle-aged females 0.072 ±0.002 



In old females 0.077 ± 0.004 



Although there is a slight progressive increase in the relative 

 nuclear volume through life, the size of the probable errors indi- 

 cates that no significance of the differences is proved. However, 

 the comparative uniformity of the relative nuclear volume seems 

 not to be due to stationary size of both nucleus and cytosome 

 during the lifetime. For, when the absolute nuclear sizes are 

 averaged, the following results are obtained: 



Size of intestinal nuclei in young adults 0.325 ± 0.0088 



Size of intestinal nuclei in middle-aged females .357 ± .0086 



Size of intestinal nuclei in old females .384 ± .0130 



While one would hesitate to ascribe significance to the difference 

 between young and middle-aged, or between middle-aged and 

 old females, the difference between young and old fulfills the 

 usual statistical requirement for significance, indicating that the 

 smaller differences between middle-aged indi\dduals on the one 

 hand and young and old females on the other are also significant. 

 There is an increase, therefore, in the size of the cytosome from 

 early adult life to old age, to maintain the comparative constancy 

 of the relative nuclear volume shown above. 



Oocytes. The mean relative sizes of the nuclei in the oocytes 

 of females of different ages were found to be as follows : 



