REPRODUCTION OF THE HYPOTRICHOUS INFUSORIA 231 



out at the 131st generation. Culture Oh was started October 

 27, 1911, by isolating an individual from the Ob culture, and it 

 was carried until February 1, 1912, on a hay infusion medium, 

 when it died out at the 159th generation. Culture Ove was 

 started October 27, 1911, by the isolation of an individual from 

 the Ob culture and it was carried until January 14, 1912, on a 

 'varied environment' medium, when it died out at the 150th 

 generation. These three were all daily isolation cultures. Cul- 

 ture Obtt, a mass culture, carried on a beef extract medium and 

 kept in test tubes, was started October 22, 1911, by the isolation 

 of an individual from the Ob culture and was carried until May 

 15, 1913, when it died out. Graphs showing the life history of 

 each of the daily isolation cultures have been plotted by aver- 

 aging the divisions in the four lines of each culture for five-day 

 periods. 



4. Three cultures of Pleurotricha lanceolata have been under 

 observation, all of which were started from descendants of an 

 original individual isolated from a laboratory hay infusion Jan- 

 uary 6, 1912. Culture Ph was started January 9, 1912, and 

 was carried on a hay infusion medium until September 25, 1912, 

 when it died out at the 656th generation. Culture Pb was 

 started January 9, 1912, and was carried until May 1, 1913, 

 on a beef extract medium, when it died out at the 943d gener- 

 ation. Both of these were daily isolation cultures. Culture 

 Phtt, a mass culture kept in test tubes on a hay infusion medi- 

 um, was started January 9, 1912, and has, so far, been carried 

 over 22 months and gives every evidence of being able to live 

 indefinitely. Graphs showing the life history of each of the 

 daily isolation cultures have been plotted by averaging the divi- 

 sions in the four lines of each culture for ten-day periods. 



5. The study of the graphs in all the daily isolation cultures 

 of both species reveals what might be termed typical 'life cycles' 

 in these organisms. 



6. The study of the prepared material shows that, although 

 the animals at the beginning of the work gave every evidence of 

 a normal morphological condition, previous to the death of a 

 culture atypical and degenerate individuals appear and these 



