NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 



307 



very plain that there was no one-sided grouping of the data, the 

 cells of a given size being spread rather evenly over the genera- 

 tions, and the cells of one generation being distributed fairly 

 uniformly with respect to their size. Hence, although the inclu- 

 sion of cells of various sizes greatly increased the probable error 

 of the mean, it could not have altered the mean itself very much. 

 A further test of the significance of the relative nuclear size 

 with relation to the life-cycle was obtained in the following man- 

 ner. It is well known (Shull, '12) that whether a rotifer is to be 



TABLE 5 



Variation in the relative nuclear volume of oocytes of Hydatina senta, with reference 

 to size {stage of growth) of the cells 



a male-producer or a female-producer is decided in the preceding 

 generation, that is, while the egg from which the rotifer develops 

 is still in the body of the mother. If, therefore, relative nuclear 

 volume determines the proportion of male-producers, that volume 

 in generations preceding many male-producers should be dif- 

 ferent from the corresponding relative volume in generations 

 preceding no male-producers. In table 1 it is shown that there 

 were in the line studied nine generations preceding generations 

 that included male-producers. The measurements of oocytes 

 from these two groups of generations have been collected sepa- 



