CONTROL OF SEX BY FOOD IN ROTIFERS 293 



GENERAL DISCUSSION 



Probably the production of the male-producing females in all 

 the experiments with the five different species of rotifers can be 

 explained by the quality of the food in the diet. In the experi- 

 ments with Hydatina senta, Diaschiza sterea, and Diglena 

 catellina the colorless flagellate, Polytoma, very Hkely furnished 

 a moderate amount of nutrition so that the rotifers lived and 

 reproduced at a moderate rate. When the rotifers were trans- 

 ferred to the green diet they probably ate about the same amount 

 of food but might have digested and assimilated it more easily 

 and faster, and consequently the formation of eggs was more 

 rapid. However, in some way, as yet unknown,, the green diet 

 changed the mechanism of the eggs in such a manner that in- 

 stead of developing into female-producing females they developed 

 into male-producing females. Moro has shown in her chemical 

 experiments with Brachionus pala that a mother forms and 

 extrudes the eggs that develop into male-producing daughters 

 very much faster than a mother that is forming and extrud- 

 ing eggs which develop into female-producing daughters. The 

 ratio was 4 to 1. 



In my experiments with Brachionus pala and a pure Chlamy- 

 domonas diet it has been found that a mother produces very 

 few eggs that develop into male-producing daughters when she 

 is kept on a scanty diet but when the diet of the same flagel- 

 lates in the same culture water is made abundant or superabun- 

 dant the mother produces many eggs which develop into male- 

 producing daughters. Thus showing that there is something 

 in an abundant diet that causes a mother to produce male- 

 producing daughters. 



Moro concludes that sudden changes of temperature, either 

 the raising or the lowering of it, causes mother's to produce 

 male-producing daughters. In Hydatina senta Punnett, Whit- 

 ney, and Shull have found no evidence to support this con- 

 tention. In the recent experiments with Diaschiza sterea and 

 Diglena catellina the temperature was that of the room at all 

 times. These rotifers in the Polytoma diet produced only fe- 



