LIFE-HISTORY OF ROTIFER 241 



or decrease the ratio of the third and fourth antennal segments. 

 He concluded that "Selection from among extreme variants 

 does not alter the mean as obtained for the strain without selec- 

 tion. The offspring of an extreme variant may show, not a 

 reversion to the mean of the line of a strain, but a reversion 

 which swings pendulum-like much beyond the mean .... only 

 to be brought back to its former side of the mean-of-the-strain 

 base line in the next generation." In the second paper this 

 pendulum-like swinging of the mean for the offspring was tested 

 through seven generations with the conclusion that "regression 

 within a pure line of a parthenogenetic form does not follow 

 Galton's law. . . . but .... is somewhat pendulum-like, swinging 

 beyond the mean of the strain, or line." In the last paper 

 extensive experiments carried on with the cornicles, the antennae, 

 and the body length yielded results which pointed to the con- 

 clusion indicated in the earlier work, that selection in a partheno- 

 genetic line had no lasting effect. 



At the present time, then, experimental data on uniparental 

 inheritance point in opposite directions, some work indicating 

 that selection within a pure line is ineffective (Johannsen, 

 Jennings, Ewing, and many botanists), other work, that selection 

 is effective (Jennings, Middleton, Root, Hegner). There was 

 some indication in Proales that an increase in length of Ufe 

 and in number of eggs produced had taken place during the time 

 of cultivation in malted milk. A comparison of 100 organisms 

 isolated in February, 1919, with 100 organisms isolated in 

 June, 1919, shows an increase in average egg production from 

 12.79 to 23.43, with an iacrease in maximum production from 

 23 to 30. This increase in egg production was accompanied by 

 an increase in individual range of life from 3 to 5 days to 2 to 7 

 days. Such increase in egg production and length of life sug- 

 gested that by selection the maximum in both these might be 

 increased still further. An experiment was therefore under- 

 taken to test this. In this experiment in selection an attempt 

 was made to eliminate variations in the conditions as much as 

 possible; the food was prepared carefully from the same jar of 

 malted milk, with water from the same spring throughout the 



