438 LORANDE LOSS WOODRUFF. 



such as markedly different culture media and temperatures on 

 rhythms and endomixis. It seemed important to obtain a more 

 definite background of knowledge of the influence of what 

 perhaps may be called normal environmental changes before 

 attempting to study the influence of, for example, specific chem- 

 ical agents on the process. 



It is assumed in the present paper that the reader is familiar 

 with the earlier work on Paramecium which has been published 

 from the Yale Laboratory. 



MATERIAL AND METHODS. 



The organisms employed in the work were from pedigreed 

 cultures of Paramecium aurelia. Some of these had been under 

 culture conditions for long periods one for more than 5,000 

 generations while others were started with this work in mind. 

 Each of the five races used was started originally with a 'wild' 

 individual which was secured from a locality far removed from 

 that of the others, so that representative diverse material was 

 afforded. The early life history of each of these cultures has 

 been presented in connection with other work and the reader is 

 referred to these papers for further details. 1 



All the organisms studied have been carried in pedigreed 

 subcultures isolated from the respective main cultures of the 

 various races, and since the method of conducting such cultures 

 has been described many times in earlier papers it need not be 

 repeated in detail here. Suffice it to say that the method 

 involves the isolation of one or more animals from each line of 

 every subculture practically every day and in addition, for 

 the work in hand, the preservation and cytological study of 

 some of the stock animals left over at the time of the daily 

 isolations. In this way the occurrence of endomixis has been 

 determined. 



The main cultures have been carried on the 'varied' culture 

 medium which we have found for ten years so favorable in 

 breeding Paramecium. 2 This consists of infusions of vegetable 

 and animal debris collected from time to time from laboratory 



1 Cf. especially Woodruff, BIOL. BULL., XXXIII., 1917. 



2 Woodruff : "The Life Cycle of Paramecium when Subjected to a Varied 

 Environment," American Naturalist, XLII., 1908. 



