484 



AUSTIN RALPH MIDDLETON 



TABLE 10 



Experivient 1-D: Actual number of geherations and selections per 30 lines per ten- 

 day period during the five ten-day periods of the second reversed selection of the 

 lines of Experiment 1 



The lines from the experiment in reversed "selection (Experi- 

 ment 1-D) just described were next continued under the bal- 

 anced selection method for two ten-day periods in order to de- 

 termine whether the differences in the reverse direction obtained 

 in that experiment were true heritable differences of fission 

 rate. The animals were transferred to fresh slides daily. Figure 

 13 shows the polygon of the average fission rates of these two 

 sets of lines and table 11 gives the actual number of generations 

 produced by each set. From these it appears that the average 

 daily difference of fission rate per line between the two sets of 

 lines is 0.38 generation in favor of the fast selected slow set. 



It is therefore clear that reversed selection had really pro- 

 duced an heritable difference in fission rate in favor of the 

 former slow lines; the relative rates of fission of the two sets 

 was now reversed. As before remarked, this result is to be 

 expected; the earlier experiments show that direct selection pro- 

 duces hereditary differences in one direction; reversed selection 



