LIFE CYCLE OF HYDATINA SENTA 141 



cases there presented, where differences in the proportion of 

 male-producers were obtained within the same pure line. That did 

 not, however, exclude the possibility that such internal differences 

 do exist. In the hope of finding pure lines showing different 

 behavior with respect to the life cycle, search was made for 

 rotifers in different localities near New York. But this species 

 was nowhere found except at Grantwood, N. J. Eventually some 

 specimens were obtained from Baltimore, Md. 



Experiment XXXII. A culture of Hydatina was obtained from 

 Baltimore through the courtesy of Prof. H. S. Jennings, and 

 brought to New York, on March 23, 1910, by Prof. T. H. Morgan. 

 The culture was labeled "Hydatina (Old Culture) Curtis Bay, 

 March 6." One of the females from this culture was isolated 

 March 23, and from her sixty successive generations were bred. 

 On the same day, a female was isolated from the pure line used 

 as control in Experiment XVHI, which was originally obtained 

 from New York, as described in that experiment. From this 

 female over fifty generations were reared. Both pure lines were 

 bred in Great Bear spring water, and the same food was used every 

 day for both. The conditions were kept as nearly alike as possible. 

 It was believed that any internal difference between the two lines 

 would be shown in so large a number of generations. In table 

 34 the two lines are compared in detail. 



In the three months and a half through which this experiment 

 extended, the New York line produced only 11.1 per cent of 

 male-producers, the Baltimore line 18.5 per cent. Had such a 

 difference been obtained in any of the experiments with external 

 agents, it would have been taken as good evidence of a positive 

 effect of the environment. It can scarcely be regarded as other 

 than good evidence here. The difference is not due to some sudden 

 increase in the number of male-producers in one line without a 

 corresponding increase in the other line, for taken by and large 

 the periods of many male-producers occur about the same time 

 in both lines. Nor is the difference in the two percentages due 

 to the fact that the experiment was terminated at one time rather 

 than at another; for the experiment could have been brought to a 

 close at any time, even after a single generation, and the Balti- 



