REPRODUCTION OF THE HYPOTRICHOUS INFUSORIA 213 



peared to be a typical 'life cycle/ it would then be evident that 

 they had not died through the ending of a definite life cycle, due 

 to an inherent condition of senescence, but because the culture 

 conditions had not been entirely suitable, inasmuch as 'sister 

 cells' under other culture conditions were able to live indefinitely. 

 In one of the two species employed in this work, Pleurotricha 

 lanceolata, these expectations have been realized. The experi- 

 mental work embraces a study of the following points: 



1. The life history of Oxytricha fallax when bred in beef ex- 

 tract, hay infusion and Varied environment' media under the 

 conditions of daily isolation cultures. 



2. The life history of the same organism when bred in a beef 

 extract medium in mass cultures in test tubes. 



3. The hfe history of Pleurotricha lanceolata when bred in 

 beef extract and hay infusion media under the conditions of 

 daily isolation cultures. 



4. A study of a mass culture of Pleurotricha lanceolata kept 

 on a hay infusion medium in test tubes. 



These experiments have been carried on during a period of 

 two years in the following laboratories: Sheffield Biological Labo- 

 ratory and Osborn Zoological Laboratory of Yale University, 

 Biological Laboratory of Central College, Bella, Iowa, and the 

 Marine Biological Laboratory, Woods Hole, Massachusetts. 



The writer desires to acknowledge his great obligation to Pro- 

 fessor Lorande L. Woodruff for suggesting the problem and for 

 the splendid assistance given during the course of the work, and 

 also to Professor Alexander Petrunkevitch for assistance in mak- 

 ing the microphotographs, 



II. METHODS 



In Part I of these studies is given a full description of the 

 methods used in carrying on the daily isolation cultures, the 

 making of the beef extract, hay infusion and Varied environment' 

 media, the preparation of permanent specimens, and so forth. 

 Inasmuch as all of these methods have been used in the present 

 paper without modification, the reader is referred to the previous 

 paper for these details. 



