556 D. D. WHITNEY 



strains and mixed cultures for other strains, or he may have used 

 a mixed food culture whose protozoan fauna was stable or varied 

 according to the light conditions or possibly other conditions in 

 the laboratory. 



In order to cause rotifer mothers to produce male-producing 

 daughters by changing the diet from Polytoma to Dunaliella 

 the latter diet must be very abundant so that the mothers may 

 consume enormous quantities of it. A change to a meagre diet of 

 Dunaliella causes no male-producing daughters to be produced. 

 This fact that the Dunaliella diet must be very copious in order 

 that male-producing daughters may be produced, rather indicates 

 that a sudden change in metabolism in which the processes are 

 carried on at their maximum rate, may be a necessary accompany- 

 ing stimulus, coupled with the new diet stimulus that causes 

 male-producing daughters to be produced. 



SUMMARY 



1. In the parthenogenetic reprpduction of Hj^datina senta 

 the influence of the diet acting upon the grandmother determines 

 the sex of the grandchildren. 



2. A continuous diet of the colorless flagellate, Polytoma, 

 causes female grandchildren to be produced. 



3. A sudden change of the diet from Polytoma to an abundant 

 supply of the active green Dunaliella causes male grandchildren 

 to be produced. 



4. The regulation of the sex ratio in the parthenogenetic 

 reproduction of Hydatina senta therefore can be controlled by 

 food conditions. 



Middletown, Conn. 

 August 14. 1914 



