CONTROL OF SEX BY FOOD IN ROTIFERS 287 



In fact in some old cultures where there were great numbers 

 of these full sized flagellates in an active state but not dividing 

 the rotifers died from starvation. The rotifers are transparent 

 and one can see the food in their stomachs after they have eaten. 



By adding fresh stable tea or bouillon or both to the cultures 

 enormous numbers of the small sized Chlamydomonas were 

 produced and in a short time the jars were swarming with fe- 

 male rotifers each of which was carrying many small male eggs. 

 Then if no fresh stable tea or bouillon was added nearly all 

 the flagellates were soon eaten, and consequently nearly all 

 the rotifers died. After a short time the few flagellates that 

 had escaped would increase their numbers considerably and the 

 few rotifers that had escaped starvation could thus get a mod- 

 erate amount of food. Soon the flagellates and the rotifers would 

 form a balanced culture and continue thus for many days. In 

 this balanced condition nearly all female-producing females 

 were produced. However, if fresh stable tea or bouillon were 

 added again to the culture an enormous increase in the num- 

 bers of the small sized Chlamydomonas took place accompanied 

 by a rapid increase of the female rotifers. Soon a very high 

 percentage of these females would be carrying male eggs. Thus 

 it is shown that a moderate amount of the diet Chlamydomonas, 

 will cause only female-producing females to be produced but 

 that an abundant diet or a superabundant diet of the same 

 Chlamydomonas will produce in some experiments as high as 

 90 per cent of male-producing females. 



The details of these experiments with a pure culture of Chlamy- 

 domonas are seen in table 6 and a semi-diagrammatic plotting of 

 the average results of the nine experiments are seen in diagram 

 7. Diagrams of the different stages in the life cycle of Chlamy- 

 domonas is seen in figure 6. 



