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ROBERT T. HANCE 



through the hot weather in a very healthy condition although 

 the cultures had remained in a room and in which the temperature 

 was at times quite high. Cultures are being carried along at 

 present that are nine months old and although most of the ani-' 

 mals have died there are still a few very active paramoecia 

 remaining. 



The division rate for this race has a somewhat wider range than 

 I have observed in the case of other races. Under normal con- 

 ditions (fresh or nearly fresh hay infusion) these animals divide 

 from one to three times in twenty-four hours. When the cul- 

 ture medium is older the rate may drop below this. There have 

 been times, however, when the animals under observations di- 

 vided as rapidly as five times in twenty-four hours and this 

 rate was maintained for six or seven days. This rate of division 

 is much more rapid than is usual for the two-vacuoled races. 



In an attempt to determine whether or not the rapidity of divi- 

 sion is the sole agent in the production or inhibition of the for- 

 mation of extra vacuoles, several single individuals were isolated in 

 watch glasses containing hay infusions that differed widely in 

 age and condition. Three sets of experiments were set up in 

 each kind of infusion and in three days the number of divisions 

 that had occurred and the percentage of two, three and four- 

 vacuoled animals that were present was recorded for each of the 

 three sets of experiments and for each type of medium. The 

 results obtained in each infusion were averaged and are given 

 below. All the experiments were repeated to determine whether 

 the results of the first set would be constant. The cultures 

 from which the animals for this experiment were drawn was 

 started from a single individual. The number of divisions given 

 is for a period of three days. 



