THE PRODUCTION OF MALES AND FEMALES CON- 

 TROLLED BY FOOD CONDITIONS IN THE 

 ENGLISH HYDATINA SENTA. 



DAVID D. WHITNEY. 



It has been found recently in an American parthenogenetic 

 strain of the rotifer, Hydatina senta, from New Jersey that a 

 continuous diet of the colorless protozoan flagellate, Polytoma, 

 causes practically all females to be produced. 1 This production 

 of only females can be maintained in this manner through 

 generation after generation for several years. If, however, the 

 diet is suddenly changed to a green protozoan flagellate, Chlamy- 

 domonas, that is in an active state, males can be produced in 

 great numbers. 



It has been suggested that perhaps this phenomenon of the 

 regulation of the two sexes by food conditions is peculiar to this 

 particular strain of New Jersey Hydatina senta and is not an 

 universal characteristic of the species. Fortunately it has been 

 possible to test this hypothesis on an English strain of Hydatina 

 senta and some very clear and conclusive results have been 

 obtained. 



I am greatly indebted to A. F. Shull for the stock of English 

 rotifers with the accompanying data. 'The English line was 

 received from Mr. C. F. Rousselet, who collected them as resting 

 eggs in mud at the bottom of a duck pond in England in August, 

 1912. They were sent to me about November I, 1912, in dry 

 dirt. The first ones hatched a few days later and from them the 

 line sent to you has been reared by parthenogenesis ever since. 

 As they were reared there was a generation about every three 

 days and so you have about the 27Oth generation." The stock 

 of this English line was received from Dr. Shull on January 7, 



I9I5- 

 The females of this strain produce fewer offspring in the same 



period of time than the females of the New Jersey strain. This 



1 Jour. Exper. Zoo/., Vol. 17, November, 1914. 



41 



