456 AUSTIN RALPH MIDDLE TON 



found to be divided, while the other was not, a selection was 

 made (fig. 1). If the line is under selection for the production 

 of a rapid rate of fission, the two progeny of the individual that 

 has divided are transferred to the new slide, while the undivided 

 individual is rejected. In selection for a slow rate of fission, 

 on the other hand, the individual not yet divided is selected for 



Fig. 1 Diagram of successive fissions among the progeny of a single indi- 

 vidual, illustrating the variations in fission rate which were the subject of selec- 

 tion in the present work. The left side of the figure traces a series of 'fast' 

 selections, the right side a series of 'slow' selections, showing that at a given 

 moment we may have, among the progeny of a single parent individuals of the 

 fourth and of the second generation. 



propagating the stock. This process is continued: a ^selection' 

 is made and counted whenever one of the two parents is found 

 to have thus divided before the other. 



EXPERIMENTS TO TEST THE EFFECT OF SELECTION ON THE 

 FISSION RATE WITHIN A SINGLE CLONE 



1. The first series of experiments 



Experiment 1, part 1. Direct selection in opposite directions, 

 November 3 to December 3, 1913. 



On November 3, sixty animals of the sixth generation from 

 a single individual which had been isolated from a 'wild' labora- 



