FOOD AND OXYGEN IN CONTROLLING SEX 133 



experiment and one is allowed to stand in ordinary air conditions 

 and the other one is put under an excess of oxygen it seems a 

 matter of chance just what will happen. In a majority of the 

 experiments the cultures under the influence of oxygen contained 

 many more organisms at the end of twenty-four hours than did 

 the cultures under air conditions but in some experiments the 

 cultures under oxygen conditions contained fewer bacteria than 

 those under air conditions. Whether the bacteria furnish the 

 food for the protozoa in the zooglea and the protozoa are eaten 

 by the rotifers or whether the rotifers eat both the bacteria and 

 the protozoa is immaterial. However this may be, the bacteria 

 are the original source of food supply for the rotifers in these 

 cultures of colorless microorganisms. 



With the present technique of manipulating the rotifers and 

 their food cultures of zooglea it seems to be a matter of chance 

 what the food conditions will be both at the beginning and at 

 the end of a parallel series of experiments extending through 

 twenty-four hours either under air conditions or under oxygen 

 conditions. This, of course, can be readily explained as being 

 due to the chance development and ascendency of any of the 

 various species of bacteria in the zooglea. 



Table 16 from the paper of Shull and Ladoff is here inserted to 

 show a fine example of this chance development of optimum food 

 conditions. 



Under air conditions nine mothers out of a total of twenty- 

 two mothers produced nearly all of the male-producing daugh- 

 ters and under 60 per cent oxygen conditions seven mothers 

 out of a total of twenty mothers produced nearly all of the 

 male-producing daughters. The total summary shows those 

 mothers which were under air conditions produced more male- 

 producing daughters than did those mothers which were under 

 oxygen conditions. Opposite results are shown in the present 

 inserted table 19 of Shull and Ladoff. Why do these experi- 

 ments disagree? Shull and Ladoff assert that it is because one 

 was a New Jersey race and the other was a Nebraska race of 

 Hydatina senta that was used in the respective experiments! 

 It is conceivable that if the experiments of Shull and Ladoff in 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 24, NO. 1 



