COMPETITION FOR COMMON FOOD IN PROTOZOA 



99 



process of competition was studied in 21 microcosms for a period of 

 25 days. Table IX shows the combinations of separate species of 

 Protozoa which were used. Let us first of all analyze the competition 

 between Paramecium caudatum and Paramecium aurelia. The data 

 on the growth of pure and mixed populations of these species are 

 presented in Table 3 (Appendix) which gives the number of individ- 

 uals in a sample of 0.5 cm 3 taken from a culture of 5 cm 3 in volume. 

 (A separate counting of the number of individuals in every culture 

 was discontinued from the twentieth day, and we began to take 

 average samples from the similar cultures.) 



Fig. 20. Paramecium caudatum (1) and Paramecium aurelia (2) according to 

 Kalmus ('31). (3) Measurements for the calculation of volume of Para- 



mecium. 



In order to investigate the process of competition, we had to pass 

 from the number of individuals of P. caudatum and P. aurelia to their 

 biomasses, as these species differ rather strongly in size (see Fig. 20). 

 In order to obtain an idea of the biomass we had recourse to the vol- 

 umes of these species. P. caudatum and P. aurelia were measured 

 under the conditions of our experiments (Table X) and on the basis 

 of these measurements the volumes were calculated. As in shape 

 Paramecium after fixation approaches somewhat closely to an ellip- 

 soid of rotation with the half -axes: -, -, - (see Fig. 20), the calcula- 



a Ji a 



tion of the volumes was made according to the formula for this body. 



