536 



WALDO SHUMWAY 



has been one-half strength standard hay infusion used after 

 coohng. The life history as averaged for ten day periods is 

 shown in figure 3. 



In this connection it may be pointed out that the last two 

 races, B' and C, were derived from a single reorganized indi- 

 vidual of an endogamous conjugant and present protoplasm as 

 homogeneous as possible. It will also be observed that these 

 conjugations serve as logical starting points for the life histories, 

 a point of considerable importance for experiments such as these, 

 in view of the fact that the protoplasm of Paramaecium is in 

 different conditions at different stages of the life history. 



Aug. 



Si 



Oct 



No K 



''^^^^ 



lOO generations 



Fig. 3 Graph showing life history of the C race in average daily division 

 rate re-averaged by ten day periods. 



FEEDING EXPERIMENTS 



a. On the A race. Nine experiments on this race of Paramae- 

 cium aurelia in which parallel hues were maintained on hay in- 

 fusion and thyroid media are here cited (tables 1 to 9) ; a summary 

 (table 10) is added for comparison with the results obtained with 

 Paramaecium caudatum. The relation of the different experi- 

 ments to the life cycle of the race is shown in figure 1, where the 

 points at which the experiments were begun are indicated by 

 roman numerals. 



Experiment A 1 was initiated by extracting two lines from the 

 control and treating one daily with thyroid, the other with thy- 

 mus. These gland preparations were from three sources, a, 



