FISSION RATE OF STYLONYCHIA PUSTULATA 



483 



an average difference of 0.27 generation established in the reverse 

 direction. 



If this difference shows itself to be heritable, it will appear 

 that it is probably due to the large number of selections prac- 

 tised within the relatively short period of fifty days ; it will indi- 



I 



:J 



10 30 50 



Fig. 12 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-D 

 (reversed selection) . The continuous line of the curve of the former fast lines 

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

 fast-selected. The ordinates are the averages per ten-day periods, the abscissae 

 the ten-day periods. 

 * 



cate that the alteration of fission rate is proportional to the 

 number of selections made, rather than the length of time over 

 which the selections are distributed. This matter is tested in 

 the next experiment. 



Experiment 1-E. Balanced selection after reversed selection, 

 June 2 to June 21, 1914. 



THE JOURNAL OF EXPERIMEXTAL ZOOLOGY, VOL. i9, NO. 4 



