CONTROL OF SEX BY FOOD IN ROTIFERS 267 



from the winter eggs which are the fertilized eggs. Such eggs 

 of Hydatina senta have been found to live six years in old culture 

 water and three years in a dried state. When dried they have 

 withstood for several days the extreme low temperature of 

 liquid air which is about — 191°C. and also they have withstood 

 as high a temperature as +110°C. for a few hours. Moreover, 

 it has been found that species of rotifers that produce fertilized 

 eggs cannot themselves be dried and later be revived by plac- 

 ing in water as is true of those rotifers which do not produce 

 fertilized eggs. 



These females of Brachionus pala continued to live and to 

 reproduce rather slowly in the culture jar of bouillon and water. 

 From this stock jar females were taken and many preliminary 

 experiments were carried out in attempts to find optimum food 

 conditions. Finally it was found that when bouillon cultures, 

 inoculated with the miscellaneous green flagellates that developed 

 from the same mud from which the rotifers developed, were 

 placed in direct sunlight they developed very fine food cultures 

 for the rotifers. In order to prevent the temperature of the 

 culture jars from rising too high in the direct sunlight and there- 

 by killing all the flagellates as well as the rotifers that might 

 be in them, the jars were placed in a large pan through which 

 tap water flowed. In this way the temperature could be regu- 

 lated at will and was not allowed to rise above 35°C. to 37°C. 

 The green flagellates seem to be the most active at this temper- 

 ature and as the rotifers could eat them only in an active state 

 all the cultures were usually kept in this pan. At night and on 

 cloudy days the temperature would be the same as the room 

 temperature of about 20°C. 



The stock solution of bouillon was made by boiling one Ar- 

 mour's beef bouillon cube in 400 cc. of tap water. 



The bouillon culture of green flagellates was allowed usually 

 to stand from several days to several weeks in direct sunlight 

 with occasional additions of fresh bouillon. During this time 

 several inoculations with the rotifers were made and usually 

 at the end of a few days there would be a good culture of both 

 the green flagellates and the rotifers. After some time if no 



THE JOURNAL OF EXPERIMENTAI- ZOOLOGY, VOL. 20, NO. 2 



