508 JENNINGS— HEREDITY IN PROTOZOA. LAprii 24, 



microns ; for i it was 88.268 X 30.268. On this date I placed in 

 separate watch-glasses the ten largest specimens of g and the ten 

 smallest specimens of i, keeping them under the same conditions. 



On November 29 I again selected from the progeny of these the 

 ten largest g and the ten smallest i, destroying the others. 



On December 7 the same selection was repeated ; the remainder 

 of each lot was killed and measured. The mean measurements were 

 g, 120.590 X 41-115 microns. 

 i, 98.709 X 34-2o8 microns. 



Thus, in spite of the fact that for at least fourteen generations 

 we have selected for propagation the largest of g and the smallest of 

 i, g has become smaller and i has become larger! The results of 

 selection, if there are any, quite disappear in comparison with the 

 effects of slight environmental dififerences. 



In spite of this discouraging result, the experiment was con- 

 tinued. On December 16 I selected the five largest g and the five 

 smallest i and again measured the rest of each. The results were 

 g, 127.059 X 38.588 microns. 

 i, 98.608 X 29.739 microns. 



Thus, i retains the same length, while g has increased, but has not 

 regained the length it had at the beginning of the experiment. 



On December 25 the five largest g and the five smallest i were 

 again selected for propagation. 



On December 30, thirty-seven days after the beginning of the 

 experiment, I again measured all but the five largest of g and the 

 five smallest of i. The results are 



g, 112.600 X 30.300 microns. 

 i, 86.756 X 22.062 microns. 



Thus, i has decreased as compared with its original length, while 

 g, which was selected for increase of size, has decreased a great 

 deal more ! The decrease in length of i is less than two microns ; 

 the decrease in g is more than sixteen microns ! And this is the 

 result of five selections, taking for g the largest, for i the smallest, 

 specimens produced in the course of at least thirty generations !^ 



' The number of specimens on which the measurements are based will 

 be found in Table XXIIL, page 488, which includes, for another purpose, the 

 measurements from these experiments. 



