Determniation of Sex ni Hydatina senta c 



Experiment II, temperature 14° C. Five female-laying females, 

 kept from the time of hatching at this temperature, produced no 

 eggs; 24 per cent developed into male-laying females. 



The same five female-laying females were then placed at a tem- 

 perature of 26° to 28° C. and produced 81 per cent male-laying 

 females. 



Experiment III, temperature 14° C. Six female-laying females 

 which had been kept at this temperature from the time of hatch- 

 ing produced 34 eggs, of which 12 per cent developed into male- 

 laying females. 



The same six female-laying females were then placed at a tem- 

 perature of 26° to 28° C. and allowed to produce 44 eggs, of which 

 95 per cent developed into male-laying females. These six females 

 were alternately placed at 14° C. and 28° C. several times and 

 always gave a high percentage of male-laying females at the 

 higher temperature. 



2 Author s Experiments 

 a Temperature 20° to 22° C. 



Experiment I, October 24, 1906. A female-laying female was 

 isolated from a jar which was stocked with rotifers collected Octo- 

 ber 2, from the same pool in which the animals were found in the 

 preceding spring. 



This strain was carried through twelve generations and the 

 percentage of male-laying females determined. Each female was 

 supplied with an abundance of food from the time of hatching, 

 isolated in a separate watch-glass, and kept upon the laboratory 

 table at room-temperature. 



Table I gives the ratio of the mother individuals producing 

 male and female offspring in the 3264 daughter-females of 95 

 female-laying females in the twelve generations. 



This experiment was made in order to obtain the percentage 

 of male-laying females produced at room temperature of 20° to 

 22° C, in order to be able to have some standard percentage of 

 male-laying females with which to compare the results of the 

 experiments conducted at lower and higher temperatures. 



