NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 319 



might lead one to assign to them a significance in relation to the 

 life-cycle, but in each case tests of the same phenomena in other 

 ways have negatived such an assumption. 



2. The relative volume of nuclei in the yolk gland increased 

 steadily through a series of nineteen generations. This increase 

 was due almost solely to an absolute increase of the nucleus, 

 while the volume of the cytosome remained nearly stationary. 

 The significance of this nuclear enlargement is discussed. 



3. The relative nuclear volume of cells in the stomach-intestine 

 remained on the whole nearly constant through the first ten or 

 twelve generations of the line on which this study was based, and 

 then decreased somewhat to the end of the series (nineteen genera- 

 tions). This decrease was apparently due to absolute decrease 

 of the size of the nuclei, not to a change of the cytosome. 



4. The relative volume of the nuclei of the oocytes appeared 

 not to change during nineteen generations. Determination of 

 'long range' changes in the nuclei of the oocytes is made difficult, 

 however, by a marked change in the relative nuclear volume 

 during the growth of each cell. The ratio of nuclear volume to 

 cytosomal volume is about five times as great in a moderately 

 early stage of growth as it is when growth is nearly completed. 



5. The ratio of nuclear volume to cytosomal volume in the 

 yolk gland increases considerably during the lifetime of the 

 individual. This increase is brought about by an increase of the 

 absolute size of both nuclei and cytosome during early adult life, 

 and a decrease of the absolute size of both nuclei and cytosome in 

 later life. The absolute increase referred to is relatively more 

 rapid in the nuclei than in the cytosome, while in later life the 

 decrease is less rapid in the nuclei than in the cytosome. The 

 net result is a steady increase of the relative nuclear volume 

 throughout life. 



6. The absolute size of both nuclei and cytosome in the stom- 

 ach-intestine increases with age, the nuclear increase being 

 perhaps slightly the more rapid. Hence the relative nuclear 

 volume is nearly stationary throughout life, or perhaps increases 

 slightly with increased age. 



7. The relative nuclear volume of the oocj^tes probably does 

 not change with the age of the female. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 35, NO. 3 



