434 H. S. JENNINGS AND K. S. LASHLEY 



were cultivated side by side in the two concavities of a single slide. 

 In changing the animals to new fluid, it appears possible that the 

 pipette, after transferring a, would retain some of the bacteria 

 from the a drop, and mingle it with the h drop, when h was 

 changed. Thus possibly the bacterial content of the cultures of 

 the two members of pairs might be on the whole a little more 

 uniform than that of two cultures taken at random; this might 

 cause the rate of reproduction to be a little more alike in the two 

 members of pairs or of split pairs, producing a correlation. 



For these and other reasons it was determined to undertake 

 a very extensive experiment, giving numbers sufficiently large 

 to make the results reliable, and at the same time fulfilling all 

 conditions which the experiment demands. For this purpose 

 the two authors of Part II joined forces, since it is physically 

 impossible for one person to care for so many ' cultures as are 

 required. 



We shall call this Experiment 16, in order that there may be 

 no confusion with Experiments 1 to 15 described in the senior 

 author's paper on the Effects of Conjugation (this Journal, vol. 

 14, 1913, pages 279-391), since in the present paper it is neces- 

 sary to refer frequently to these fifteen experiments. In Experi- 

 ment 16 as carried out, 482 strains, derived from the two members 

 (a and h) of 241 pairs of conjugants, were propagated forty- 

 seven days, an exact record being kept throughout of the num- 

 ber of fissions for each strain; also of the dying out of strains. 

 The important facts as to the culture methods used are as 

 follows : 



On March 23, 1912, 250 pairs were isolated from watch glasses 

 that had been taken the night before from a wild culture of Para- 

 mecium caudatum. Accidents later reduced this number to 

 241 pairs. As soon as the two members separated, they were 

 transferred to separate shdes, giving us thus 482 distinct strains. 

 To each pair a number was given, while the two individuals form- 

 ing the pair were called a and 6; the progeny of each of these 

 received the same designation. Each strain was therefore desig- 

 nated by a number and a letter, giving precisely its origin and 

 relationship; the designations running from 1 to 241, a and h. 



