FOOD AND OXYGEN IN CONTROLLING SEX 117 



on the surface of the water in the jars. This gas caused the 

 glowing end of a burning match to glow more brightly when it 

 was suddenly thrust into a bubble. Presumably this gas was 

 oxygen. However, very few if any male-producing females were 

 produced in these jars in which there was this excess of oxygen. 

 In experiment 2 of table 6 are shown the results of a balanced 

 culture jar containing green microorganisms and the marine 

 rotifer, Brachionus mulleri. At this time about 3 to 4 per cent 

 of the females were carrying male eggs. Compressed oxygen from 

 a cylinder was allowed to pass through this culture for twenty- 

 four hours. This saturation of the culture water with oxygen 

 (perhaps it was already saturated) caused no increase in the 

 numbers of male-producing females thus showing again that 

 oxygen is not a potent factor in the production of male-producing 

 females. 



THE INFLUENCE OF OXYGEN UPON COLORLESS ZOOGLEA AND IN 

 CAUSING A CHANGE IN THE RATIO OF THE FEMALE-PRODUCING 

 FEMALES AND THE MALE-PRODUCING FEMALES OF THE NEW 

 JERSEY HYDATINA SENTA 



In these experiments an attempt has been made to determine 

 the effect of oxygen upon the protozoa and the bacteria contained 

 in the zooglea. This is considered very essential because if the 

 individuals of the zooglea which are the sole food of the rotifers 

 are increased or decreased the welfare of the rotifers is at once 

 effected. An increase of the individuals in this zooglea might 

 cause better food conditions by increasing or maintaining the 

 number of individuals is to be eaten by the rotifers or it might 

 cause worse conditions for the rotifers by too great crowding 

 or by an accumulation of toxic products from the bacteria. 



The zooglea was made by putting about 40 grams of fresh horse 

 manure tied in cheese cloth into a liter of sterilized tap water. 

 This was allowed to stand twenty-four to forty-eight hours and 

 then the old manure was removed and replaced by fresh manure. 

 This process was continued for from one to three weeks. During 

 this time an accumulation of various kinds of bacteria and 

 minute protozoa would form at the surface in a scum. This 



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



