480 



DAVID D. WHITNEY 



TABLE 6 

 Showing light conditions of the days during the experiments of table 6 



EXPERIMENTS SHOWING THAT CULTURE WATER CONTAINING 



A VERY LOW PERCENTAGE OF FREE OXYGEN YIELDS 



AS MANY MALE-PRODUCING FEMALES AS CULTURE 



WATER CONTAINING A MUCH HIGHER 



PERCENTAGE OF FREE OXYGEN 



The experiments of the preceding tables 1 to 6 may be of 

 interest, but the crucial test of the effect of oxygen in causing 

 male-producing females to appear is really made in these experi- 

 ments in table 7. All of these experiments were carried on in 

 darkness and the food and culture-water conditions were the 

 same as those in the darkness experiments of table 5 with the 

 exception that the culture water containing the food was put 

 into one 1 1 -inch vial instead of being divided and put into three 

 vials. The vials in lots A were not stoppered, but were kept open 

 so that the surrounding air came into contact with the surface 

 of the water, but the vials of lots B were closed with tightly 

 fitting ground-glass stoppers. A small quantity of air, 3 cc. 

 to 0.5 cc, was left in each vial. In some experiments the vials 

 in lots B were inverted. The inclosed air bubble was changed 

 every morning and evening, otherwise both the food and the 

 rotifers would soon have died from lack of a sufficient oxygen 

 supply. 



Thirteen female rotifers were put into each vial at the begin- 

 ning of each experiment and allowed to remain three days 

 undisturbed. At the end of that time, fifty young females were 



