136 DAVID DAY WHITNEY 



pass through the water the females were carrying one to two 

 eggs but within a few hours after the oxygen began to pass 

 through the water each female was seen to be carrying three to 

 five eggs. The oxygen passing through the culture water may 

 have caused a more rapid reproduction of the protozoa or it 

 may have caused all the protozoa in the jar to have become 

 more accessible to the rotifers. It also, of course, produced 

 optimum oxygen conditions for all life processes of the rotifers. 

 Before the oxygen was allowed to pass through the culture 

 water the rotifers remained near the surface and thus were able 

 to eat only such protozoa as were at the surface but as soon as 

 the culture water became saturated with oxygen the rotifers 

 became distributed more or less uniformly throughout the cul- 

 ture water, living as readily at the bottom as at the surface of 

 the culture water. During this period of increased egg produc- 

 tion in culture water saturated with oxygen the number of male- 

 producing daughters increased only about 1 per cent or less thus 

 showing the negligible influence of oxygen in causing male- 

 producing daughters to be produced. 



When, however, bouillon was repeatedly added to this same 

 culture water a few days after the oxygen experiment had been 

 finished the number of bacteria and of protozoa were so enormous- 

 ly increased that the rotifers being furnished with such an abun- 

 dant food supply began producing more eggs until some of the 

 female-producing females were found to have as many as eight 

 eggs attached to their bodies. Soon there appeared in this cul- 

 ture male-producing females which rapidly increased in num- 

 bers until they formed 50 per cent of the total population of the 

 jar. The contrasting results obtained by oxygen and by food 

 on the same rotifers in the same culture water demonstrates 

 plainly which factor is the influential one. 



SUMMARY 



1. When the green food supply of Chlamydomonas was made 

 very abundant the rotifers Brachionus militaris, Brachionus 

 bakeri, and Euchlanis dilatata produced a high percentage of 

 male-producing daughters but when the green food supply was 



