EFFECT OF EXCRETION PRODUCTS OF PARAMAECIUM 563 

 EXPERIMENTS 



The organisms used in this work were from my pedigree cul- 

 tures of Paramaecium aurelia and Paramaecium caudatum. The 

 experiments were begun on July 24, 1910, when the P. aurelia 

 culture was at the 1903d generation and the P. caudatum was at 

 the 113th generation, and were concluded on October 4, 1910, 

 when the P. aurelia culture was at the 2070th generation and the 

 P. caudatum culture was at the 288th generation. Emphasis 

 is placed on the fact that the animals which formed the subjects 

 for the experiments had been under daily observation for over 

 forty months in the case of aurelia (which was the main 

 culture employed), and over three months in the case of 

 caudatum (which was used in certain experiments for com- 

 parison). Consequently their rate of reproduction, and the 

 exact conditions to which they had been subjected for nearly 

 three and a half years, were known in the case of the main culture. 

 Further, since the pedigree cultures were each originally started 

 with a single individual, all the P. aureha used in this work were 

 'sister cells,' and all the P. caudatum used were 'sister cells.' 

 Therefore all the experiments were performed on the 'same pro- 

 toplasm' of the respective species. Fig. 1 shows graphically the 

 average daily rate of division of the four lines of the P. aureha 

 culture again averaged for each month of its existence to the time 

 it was employed for this work.-' 



1. The effect of different volumes of culture medium on the rate of 

 reproduction of Paramaecium 



A series of four experiments, two of sixteeen days duration and 

 two of twenty days duration were made with P. aurelia. In 

 all the work it was found that sixteen to twenty days was the most 

 suitable length of time for the experiments, because those of less 

 than sixteen days appeared too short to give conclusive results, 

 and in those which were extended beyond twenty days, the ani- 



" For details of these cultures see Woodruff, Biol. Bull., 16, 4, 1909; Archiv f. 

 Protistenkunde, Bd. 21, 3, 1911; and Jour. Morph., vol. 22, 2, 1911. 



