No. 519] THE LIFE CYCLE OF HYDAT1NA SENT A 147 



however, been able to scenic winter eggs and males from 

 the same parent. Since in all cases known, a female 

 lays parthenogenetic eggs of only one sex, there can be 

 little doubt that sexual eggs and male eggs are identical. 



To test the influence of substances in the food cultures, 

 lines of rotifers were reared in the water of some old 

 cultures, from which the protozoa had been removed by 

 filtering. Various dilutions of this water were used, one 

 fourth, one half, three fourths and undiluted, as well as 

 pure spring water. The same kind and quantity of 

 food, a flagellate, Poh,t<nnn urrlla, was added to each, 

 and was found to live readily in all concentrations of 

 the filtrate. The results of eight or more generations 

 bred simultaneously under these conditions are shown 

 in Table I. 



Table I 



There is a gradual decrease in the proportion of sexual 

 females from the line bred in pure spring water to that 

 in the undiluted filtrate. The series in the dilute filtrate 

 were discontinued at this point, but those in spring water 

 and in concentrated filtrate were continued. Tn the 



without a single >e\ual female, while in spring water the 



to the end of the experiment. 



The experiment was repeated by removing to spring 

 water a female of the seventh generation of the series 

 bred, in the preceding experiment, in concentrated fil- 

 trate. The results of this change are shown in Table IT. 



