OXYGEN AND MALE PRODUCTION 481 



selected at random and isolated in watch-glasses. In some ex- 

 periments there were fewer than fifty young daughter females 

 produced, and in such cases all of the young females were iso- 

 lated as in lots B of experiments 13 and 14. An equal number 

 of young females were isolated from the control lots A. 



The quantity of free oxygen in the culture water was de- 

 termined both at the beginning and at the end of each experi- 

 ment in both lots A and lots B. Old culture water was used 

 which was made about the middle of the previous August and 

 which contained only a small quantity of free oxygen. After 

 this culture water was filtered it absorbed additional free oxygen 

 from the air in lots A, while in lots B, in the stoppered vials, the 

 quantity of free oxygen was diminished when the air bubble 

 was made small enough as in lots B of experiments 9 to 17 and 

 19. In experiments 9, 10, 12, 13, 14, and 18 the oxygen supply 

 became so low in lots B that none of the rotifer eggs hatched 

 until the vials were opened and additional oxygen was supplied. 

 In lots B of experiments 8, 11, 15, 16, 17, and 19 fewer eggs had 

 hatched than in lots A, in all of which there were more than 

 fifty young females at the end of three days. 



In lots A the free oxygen increased by absorption from the air 

 to from 6 to 8 cc. per liter, while in lots B it ranged from 6 to 1 

 cc. per liter at the end of the experiments. However much the 

 two lots, A and B, varied in their oxygen content, the per cent 

 of male-producing females produced was about equivalent in 

 each lot of the individual experiments and also in the general 

 average of the summary of all of the experiments. In fact, the 

 per cent of male-producing females in the summary of all lots 

 A and lots B is practically identical. Such equivalent results in 

 two parallel lots of rotifers, even under the same conditions, 

 never previously have been obtained by the author. 



The most striking result of these experiments is the pro- 

 duction of such a high per cent of male-producing females in 

 culture water that was nearly depleted of free oxygen. The 

 highest per cent among fifty young females was ninety-two. It 

 is recorded in lot B of experiment 5. Only two or three lots 

 exposed to the air exceeded this. 



