FOOD AND OXYGEN IN CONTROLLING SEX 131 



producing daughters within a few days after the cultures were 

 made. No green organisms were present nor was there any oxy- 

 gen being formed in the cultures. Later as the cultures became 

 older and the number of microorganisms in them became fewer 

 the production of male-producing daughters ceased entirely and 

 only female-producing daughters were produced. In some of 

 the present experiments in table 4 Brachionus mulleri produced 

 56 per cent of male-producing females when fed upon an abund- 

 ance of colorless microorganisms. In some of the control ex- 

 periments with Hydatina senta of Shull and Ladoff in which the 

 mothers were subjected to ordinary air conditions and fed color- 

 less zooglea each of several mothers produced from 50 to 56 per 

 cent of male-producing daughters. Thus the experiments of 

 Shull and Ladoff together with the author's former ones and 

 some of the present ones agree in that a mother kept under 

 normal air conditions and fed the proper colorless microorganisms 

 can produce over 50 per cent of male-producing daughters. 



In table 5 there are also some experiments with Hydatina senta 

 which show that when some mothers were put into a dark incu- 

 bator and fed green food, which could produce no oxygen in the 

 dark, produced 76 per cent of male-producing daughters. Thus 

 showing that with the proper food, conditions mothers will pro- 

 duce a high percentage of male-producing daughters in the 

 absence of an excess of oxygen. 



The general summaries of many of the experiments of Shull 

 and Ladoff expressed in tabular form would seem to indicate that 

 an excess of oxygen caused male-producing females to be pro- 

 duced. Such also is the conclusion of Shull and Ladoff. How- 

 ever, when one examines each of the several experiments of such 

 a table one sees that nearly all of the male-producing daughters 

 were produced by a few of the mothers while the majority of the 

 mothers produced female-producing daughters although all of the 

 mothers were under the influenec of an excess of oxygen. If 

 oxygen has any general influence in causing male-producing 

 daughters to be produced it should show an effect upon a ma- 

 jority of the mothers at least. Table 19 of Shull and Ladoff is 

 here inserted to show that in only three out of eleven experiments 



