FISSION RATE OF STYLONYCHIA PUSTULATA 465 



To answer this question the first seven of the fast lines of 

 Experiment 1, part 2, were each increased (by division) to four 

 and from the eighth two hues were derived, giving thirty fast 

 hues in all. Each of the slow lines of Experiment 1, part 2, 

 was likewise increased to four, with the exception of the last 

 one which was increased to six, thus giving thirty slow lines. 

 These two sets of lines were then selected for fast and slow rates 

 of fission. During the three ten-day periods of this part of 

 Experiment 1, the selection and transfer of animals to fresh 

 slides was made every forty-eight hours instead of at the close 

 of every twenty-four hour interval as heretofore. 



At the end of the first ten-day period the eight fast lines 

 which had produced the highest number of generations were 

 selected and thirty lines were derived from them, care being 

 taken that each group of ten lines, the 'fast' occupants of a 

 single moist chamber, were represented in the new set. Also 

 eight of the slow lines which had produced the smallest number 

 of generations were selected and from them thirty lines for 

 continued slow selection were derived. The same precaution 

 was taken in reference to the distribution of the selected lines 

 among the three moist chambers. These two sets of lines were 

 then selected for fast and slow fission rates during the second 

 ten-day period. Finally this same method of reduplication of 

 the fastest and the slowest lines and the subsequent continued 

 selection of the individual variations of fission rate was followed 

 through the third ten-day period. 



This method of double selection was devised with the purpose 

 of crowding as much selection into the experiment as possible, 

 in the attempt to determine whether continued selection would 

 gradually increase the previously established difference between 

 the average rates of fission of the two sets of lines. It will be 

 remembered that the difference of average fission rates between 

 the two sets of lines at the end of Experiment 1, part 2, was 

 3.57 generations per line per ten-day period as shown by the 

 fifth ten-day period of figure 3 and by table 4. The sixth 

 seventh and eighth ten-day periods of figure 3 show those differ' 

 ences for the three ten-day periods of the present part of Experi 



