S3S 



Aaron Franklin Shiill 



TABLE XII 



Showing the number of male- and female-producers in a series of families of Hydatina senta bred from the 

 first member, and another series from the last member of successive generations, all being the 

 progeny of a single individual. 



Experiment XII. The preceding experiment was repeated 

 four times. In only a few cases did the first member of a family 

 die without laying eggs, or produce males, and so make it neces- 

 sary to derive the "first-born" from a later member. Table 

 XIII gives the results in condensed form. 



Although in one case the difference in the proportion of male- 

 producers between the first-born and last-born is practically 

 zero, and in two other cases less marked than in the preceding 

 experiment, in no case was there a higher percentage among 

 the last-born. The difference is especially marked where the first- 

 born are yielding many male-producers. 



Experiment XIII. The first and fifteenth daughters of one 

 of the females of Experiment I became the parents of two 

 series of generations; one of these was bred successively from 

 the first-born, the other from the fifteenth member, with cer- 



