286 H. S. JENNINGS 



EXPERIMENTS WITH WILD CULTURES: PARAMECIUM CAUDATUM 



Experiment 1: May 4 to June 7, 1909 



As giving typical results, an experiment which was in progress 

 from May 4 to June 7, 1909, will first be presented. 



The animals were taken from a 'wild" culture of Paramecium 

 caudatum, which was brought from a pool on May 3, 1909. It 

 was found to swarm with the infusoria, and on the evening of 

 May 3 numbers of them were placed in watch glasses; at that 

 time none were conjugating. Early the next morning conjuga- 

 tion was beginning. Thirty-five pairs in the first stages of union 

 were separated in the way already described, but in 11 of these 

 one of the members was killed or lost, so that there remained 59 

 individuals that had gone through the first stages of pairing; 

 among these 59, both members were present in 24 of the 'split 

 pairs.' 



Thirty-one pairs were allowed to complete conjugation, then 

 the two members isolated. One member of one pair was lost, 

 so that from the pairs there were derived 61 lines of propagation, 

 as against 59 from the split pairs. 



In this experiment the 120 lines of propagation were changed, 

 and the records taken, every other day. The numbers of fissions 

 were grouped in weekly periods for each line. 



Thus we have before us 120 individuals undergoing propaga- 

 tion; one set of 61 have just conjugated, while another set of 

 59 were ready to conjugate, but were prevented from doing so. 

 They differ in no other way but in regard to conjugation. What 

 later difference does this make in the two sets? 



1. The first thing that we discover is that the individuals which 

 were ready to conjugate but were prevented, are by no means 

 in a depressed, degenerate condition, unable to propagate farther. 

 On the contrary, they continue to propagate in an active, healthy 

 manner. They continued to do this till the experiment was 

 discontinued five weeks later. 



2. Secondly, we notice that those which have conjugated multi- 

 ply less rapidly than those which have not. This difference is 



