ENDOMIXIS IN PARAMECIUM AURELIA. 



449 



that the periodicity of endomixis is largely independent of the 

 character of the culture medium the general environmental 

 conditions within the rather wide limits in which it has been 

 varied in parts A, B and C of this series of experiments. At 

 most the culture conditions initially influence the appearance of 

 endomixis. In other words, the organism is set, so to speak, 

 to undergo endomixis approximately once a month and this it 

 does under any more or less favorable environmental conditions. 

 A sudden change, however, of these conditions may bring about 

 endomixis slightly earlier than it otherwise would have occurred 

 but after this the usual rhythmic period of the species is main- 

 tained. 



EXPERIMENTS SERIES II. 



The experiments of this series may be outlined as follows: 



A. Study of the periodicity of rhythms and endomixis in 

 different races of Paramecium aurelia when bred in a relatively 

 large amount of culture medium supplied fresh daily. 



B. Study of the periodicity of rhythms and endomixis in 

 different races of Paramecium aurelia 



when bred in a relatively small amount 

 of culture medium changed on alternate 

 days. 



C. Study of the periodicity of rhythms 

 and endomixis in the same races of Par- 

 amecium aurelia when bred in a relative- 

 ly large amount of culture medium sup 

 plied fresh daily, and in a relatively 

 small amount of culture medium changed 

 on alternate days. 



These experiments were begun on July 

 2, 1915, and continued until February 

 22, 1916. Five different races of the 

 organism were employed. Three of 

 them (A , 0, and B} were the same FrG - 6 - 



subcultures which were used in the experiments of Series I., 

 and which had been continued during the interim that is, from 

 March, 1915, to July, 1915. Therefore the numbering of the 

 five-day periods was continued from the earlier work and the 



B 



B, 



