490 DAVID D. WHITNEY 



nevertheless, it is one of the potent factors in causing male- 

 producing females to increase in number. The author takes the 

 opposite view-point that oxygen is not influential in causing an 

 increase of the male-producing females. 



In the experiments of Shull under air conditions, the rotifers 

 produced to 52 per cent of male-producing females in indi- 

 vidual experiments and the average in the grand total pro- 

 duction of 2334 females in tables 1, 2, and 5 to 8 was 10 + per 

 cent of male-producing females. This per cent was of those 

 females produced during the first twenty-four hours of the 

 experiments. According to sample tests of such culture water 

 as constituted these experiments, the quantity of free oxygen 

 present during the twenty-four hour period was 5 -|- to 4 + cc. 

 per liter. These results comprised of the production of about 

 10 per cent male-producing females in culture water containing 

 5 + to 4 + cc. of free oxygen per liter should now be compared 

 with the author's experiments, lots B in table 7. In these lots 

 with the diminished air supply the quantity of free oxygen at 

 the end of the three-day period of the individual experiments 

 was in some instances 1 + cc, per liter. The average quantity 

 of free oxygen in all of the lots at the end was 3 -1- cc. per liter. 

 This was a lesser quantity than was found in the experiments of 

 Shull in the air. Shull obtained an average of 10 + per cent 

 male-producing females in culture water containing 5 to 4 + cc. 

 of oxygen per liter, while the author obtained an average of 74 -|- 

 per cent of male-producing females in culture water containing 

 3 + cc. of oxygen per liter. In individual lots B of experiments 

 13, 17, and 19 in which the free oxygen was never more than 2 

 cc. per liter throughout the experiment and in lots B of experi- 

 ments 13 and 17 in which the oxygen was diminished from 2 -|- 

 cc. to 1 -|- cc. per liter during the experiment, the per cent of 

 male-producing females ranged from 72 to 88. If these lots B 

 of experiments 13, 17, and 19 are compared with the parallel 

 lots A of the same experiments in which the quantity of free 

 oxygen ranges from 3 + cc. to 8 -f- cc. per liter during the three- 

 day period of the experiments, it is seen that in this increased 

 quantity of free oxygen there is no increase in the percentage of 



