9i6 Aaron Franklin Shull 



lowed, and that ratio would be fairly constant regardless of ex- 

 ternal conditions, until the parthenogenetic series was terminated. 



Whitney ('07) made more extensive experiments, including 

 several thousand individual records, which sustained Punnett's 

 conclusion that neither temperature nor food influenced the per- 

 centage of male-producers. He found no evidence, however, of 

 constant strains, for he was able to derive lines yielding many 

 male-producers from lines yielding few, and vice versa. He 

 attempted to explain Maupas's results in two ways. First, he 

 found that at the high temperature used by Maupas (26° to 

 28°C.), male-producers laid from two to four times as many eggs 

 as did female-producers. Maupas probably assumed that the 

 number of eggs was approximately the same for each, and in this 

 way, Whitney concludes, introduced an error. Second, Whitney 

 found that the male-producers appeared chiefly in the early part 

 of the family, and since the high temperature used by Mau- 

 pas reduced the size of the families, the proportion of male-pro- 

 ducers was accordingly raised. That the first explanation is 

 invalid will be shown later. On the second point, some light is 

 thrown by data given in this paper. 



In view of these conflicting results, it seemed highly desirable 

 that the whole question be reexamined. I undertook the work at 

 the suggestion of Prof. T. H. Morgan, and I am indebted to 

 him for suggestions and encouragement throughout. 



PROBLEM AND METHODS 



The problem in Hydatina, briefly stated, was to discover the 

 factor or factors, either external or internal, which determine 

 the proportion of male-producers. 



In the experiments to be described, each female was isolated 

 in a Syracuse watch-glass, and kept in about 2 cc. of Great Bear 

 Spring water. The food used was chiefly a colorless flagellate, 

 Polytoma uvella. I have had much better success with this than 

 with Euglena or its allies. It was originally secured from a small 

 stream containing kitchen drainage on the Palisades in Gran twood, 

 N. y., in June, 1909, and has been readily propagated from one 



