Life Cycle of Hydatma Senta ^^^ 



previous experiments had 1 secured more than four or five suc- 

 cessive generations of all temale-producers. 



Experiment X. The preceding experiment was repeated a 

 number of times. In each case, the two control lines were bred 

 from sisters. The old culture filtrate was not diluted in any of 

 these experiments. 



In A, Table XI, the sisters were derived from the seventh gen- 

 eration of the line bred in undiluted filtrate in Experiment IX; 

 in B, from the third generation of A above; in C, from a line bred 

 for four generations preceding at room temperature, and for ten 

 generations previous to that at a temperature of 7° to 14° C; 

 in D, from a line which had been reared for eleven generations at 

 a temperature of 7° to 14° C, and had produced about 38 per 

 cent of male-producers; in E, from the fifteenth generation of the 

 line bred in the undiluted filtrate in Experiment IX; in F,from the 

 second generation of the line in spring water in E above. 



Here again the evidence all points to the conclusion that sub- 

 stances found in old food cultures tend to reduce the proportion 

 of male-producers. When the number of male-producers is small, 

 as in some of these experiments, it is necessary to take account 

 of death losses. In Experiment IX, in the line bred in spring water 

 24 females died without reproducing; in the line bred in concen- 

 trated filtrate, 18 were lost in like manner. Had all the lost 

 females in the concentrated filtrate been male-producers, and all 

 those in spring water female-producers, the difference in the pro- 

 portion of male-producers between the two lines would noteven then 

 be entirely obliterated. That such selective deaths should occur 

 IS not likely, for in starting a series of generations m the old culture 

 filtrate, many voung females were put into the concentrated fil- 

 trate within one or two hours after hatching, and some of these 

 produced males. They and their male offspring seemed perfectly 

 healthy. I conclude therefore, that the losses by death are as 

 likely to be from among the female-producers as among the male- 

 producers. Moreover, in Experiment X, A, there were onlv two 

 losses in the filtrate, as compared with 33 male-producers in spring 

 water; and in D, only 4 females were lost in the filtrate, as against 

 49 male-producers in spring water. In these two experiments 

 (X, A and D), the death losses are entirely insignificant. 



