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
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