FOOD AND OXYGEN IN CONTROLLING SEX 137 



allowed to become scanty very few if any male-producing 

 daughters were produced. 



2. When either the colorless or the green food supply was 

 made very abundant the marine rotifers Brachionus mulleri, 

 produced many male-producing daughters but when such a 

 food supply was allowed to become scanty very few if any 

 male-producing daughters were produced. 



3. The mothers in a race of New Jersey Hydatina senta when 

 fed upon Chlamydomonas in the dark without an excess of oxy- 

 gen present produced male-producing daughters nearly as read- 

 ily as those mothers which were fed upon the Chlamydomonas 

 in the light with an excess of oxygen present. 



4. Culture waters subjected to an excess of from 40 to 60 per 

 cent of oxygen in the atmosphere for from eighteen to forty-six 

 hours caused an increase in numbers of the various kinds of 

 protozoa living in such treated culture waters. 



5. Culture waters subjected to an excess of from 40 to 60 per 

 cent of oxygen in the atmosphere for twenty-four hours caused 

 an increase in the number of bacteria present in the culture 

 water at the end of the majority of the experiments. 



6. Bacterial counts show that a series of culture dishes in an 

 experiment can not be made identical except by chance either 

 at the beginning or at the end of the experiment although all 

 dishes are apparently unjder identical conditions, 



7. With such miscellaneous mixtures of species of bacteria and 

 protozoa in the zooglea it is largely a matter of chance when they 

 are put into various kinds of more dilute culture waters which 

 bacteria and protozoa will survive or flourish and develop such 

 food conditions as will cause the rotifer mothers to produce either 

 male-producing or female-producing daughters. 



8. An excess of oxygen in the culture water does not directly 

 affect a mother and cause her to produce male-producing daugh- 

 ters but by affecting the conditions that influence an increase 

 or a decrease of the microorganisms which constitute the food 

 supply it may indirectly cause her to produce either male- 

 producing or female-producing daughters. 



