546 D. D. WHITNEY 



produced. This was accomplished by using a continuous and 

 uniform diet of the flagellate, Polytoma, reared in a solution of 

 cooked horse manure. Throughout this time in side experi- 

 ments on this strain males were produced in large numbers 

 many times by transferring the rotifers to a new mixed food 

 culture. 



Shull carried on many experiments with temperature, starva- 

 tion, and various chemicals and finally corroborated the general 

 conclusions of Punnett and Whitney that temperature and 

 starvation were negative factors in the regulation of the two 

 sexes. He, however, was able to demonstrate that the unknown 

 factor must act upon the grandmother and not upon the mother 

 in order to cause abrupt changes in the sex ratio among the pro- 

 geny. In this point he was in agreement with Maupas' work. 

 However, Shull finally concluded that this influential factor 

 that controlled the production of the two sexes was an i7iternal 

 one. 



Mitchell in working with the rotifer, Asplanchna, recently 

 has found that a continuous diet of a uniform food culture will 

 cause only females to be produced, but if the diet is changed to a 

 new food, males are produced in the third generation (grand- 

 children). He suggested that a change of food might be found 

 to be the controlling factor in regulating the production of the 

 two sexes in Hydatina senta. 



In the experiments of the previous workers upon Hydatina 

 senta very little attention has been given to any particular kind 

 of food. Usually any mixed Protozoa culture upon which the 

 rotifers would thrive was used. However, Shull and Whitney 

 used a more or less pure culture of the colorless flagellate, Poly- 

 toma, but obtained varying results. This may be due to the 

 fact that these cultures in some instances were mixed cultures 

 to a considerable extent although not suspected to be mixed. 

 Whitney's cultures were probably the same throughout the two- 

 year period in which he obtained 289 generations of females. 

 Uniform conditions produced uniform results. At that time 

 this point was not fully appreciated. 



