232 LORANDE LOSS WOODRUFF 
under identical conditions, the aurelia culture has advanced from 
the 1785th generation to the 2117th generation, or 332 genera- 
tions. This gives a difference of only eight generations in the rate 
of reproduction of the two forms during seven months (cf. fig. 1). 
These cultures obviously do not support the statement, frequently 
made, that aurelia is a weaker form than caudatum. 
Maupas remarked that P. aurelia was one of the most common 
infusoria, and Jennings found that a typical wild culture could 
MAY JUNE JULY AUG. SEPT. OCT. NOV. 
1909 
Fig. 1 Diagram showing the comparative rate of division of the pedigree 
cultures of Paramaecium aurelia and Paramaecium caudatum, when bred under 
identical conditions, from May 14, 1910, to November 30, 1910. During this pe- 
riod P. aurelia (designated by continuous line) advanced from 1785 to 2117 genera- 
tions, while P. caudatum (designated by broken line) advanced from 1 to 324 
generations. The rate of division is averaged for ten-day periods. The ordin- 
ates represent the average daily rate of division of the four lines of the cultures. 
be resolved into caudatum and aurelia groups. It has been my 
experience that it is as easy to procure one form as the other in 
the wild state. Certainly my aurelia culture, which theo- 
retically would provide individuals to the number represented 
by 2 to the 2117th power, gives more evidence of vitality and 
reproductive power than has been demonstrated for any other 
animal. 
Conjugation. I have no data in regard to the conjugation of 
either of these forms, for, so far, in all experiments with stock 
