FISSION RATE OF STTLONYCHIA PUSTULATA 



485 



in the same way produces hereditary differences in the opposite 

 direction. 



General results of the first group of experiments. The experi- 

 ments thus far described have all dealt with parts of a single 

 clone of Stylonychia pustulata; selection has been practised on 



10 20 



Fig. 13 Polygon of the average number of generations per line per ten-day 

 period produced by the fast and slow sets of lines of Experiment 1-E (balanced 

 selection after the reversed selection of Experiment 1-D). The continuous line 

 is the curve of the reversed selected former fast lines now balanced selected. 

 The broken line is the curve of the reversed selected former slow lines now bal- 

 anced selected. The ordinates are the averages per ten-day periods ; the abscissae 

 the ten-day periods. 



the variations in fission rate within the clone. For one hun- 

 dred and thirty days two halves of this clone were subjected to 

 selection in opposite directions; this produced a marked and 

 steadily increasing difference in the average fission rate of the 

 two halves. Expressing the excess of generations produced by 

 the fast-selected lines as a percentage of the total number of 



