INFLUENCE OF FOOD IN CONTROLLING SEX 555 



food for the rotifers can thus be simply explained. Under certain 

 conditions some of the Protozoa are active and others are more 

 or less quiescent, although they may be reproducing in this 

 quiescent stage. When the conditions are changed, possible 

 in other ways than temperature, the quiescent Protozoa become 

 very active, thus constituting a new diet for the rotifers which 

 eventually causes males to be produced. 



It would be interesting to know the effect of a continuous 

 feeding of a new diet upon the rotifers, but unfortunately it has 

 been impossible to use the green Dunaliella continuously as a 

 diet. They are the most active in sunlight but during the night 

 they become more or less quiescent and consequently can not be 

 used as a food by the rotifers in any appreciable numbers. 



It is very probable that other forms of Protozoa as well as 

 Dunaliella have the same stimulating effect upon female-pro- 

 ducing females of Hydatina senta in causing them to produce 

 male grandchildren because in mixed colorless protozoan cultures 

 epidemics of males often occur. It may be possible to find and 

 cultivate a colorless flagellate which will be even more effective 

 than the green one, Dunaliella, which has already been used 

 and caused the female-producing females to yield as high as 87 + 

 per cent of male-producing daughters. 



The sex strains of Punnett may be more or less due to the 

 diet used. Punnutt states that they were fed upon Euglena 

 most of the time but does not state whether the Euglena were in 

 pure cultures. In some of the food cultures made this year an 

 undetermined species of Euglena was cultivated in the same 

 kind of bouillon solution as was Dunaliella. This was an ex- 

 cellent food for the rotifers but it did not stimulate them to 

 produce males, as the Dunaliella always did when the rotifers 

 were suddenly transferred to it from a Polytoma diet. In a 

 previous paper it has been shown that a constant and uniform 

 food supply caused one family to produce only female offspring 

 through 289 generations, although males were produced in side 

 experiments when the food was changed. Punnett unwittingly 

 may have used a pure Euglena culture as food for some of his 



