Throughout the year's work 

 every effort has been made to 

 secure conjugation and encystment 

 in the mass cultures, though with- 

 out result. Furthermore, an in- 

 tensive study, involving che making 

 of more than a thousand perma- 

 nent preparations of pedigree 

 animals at all stages in the life of 

 the culture, 24 has failed to reveal 

 any indications of endomixis. 

 Therefore, it can be stated posi- 

 tively that endomixis has not oc- 

 curred in this culture, although 

 there are fluctuations of the divis- 

 ion rate somewhat similar to those 

 associated with endomixis in P. 

 aurelia and P. caudatum.-' This 

 point will be considered in detail in 

 another paper. 



As is well known, the diet of 

 Didinium nasutum is almost exclu- 

 sively confined to paramecia, and 

 it has not been possible to culti- 

 vate successfully the former with- 

 out this food. An experiment ex- 

 tending through several months 

 showed that Didinium thrives on 

 P. calkinsi just as well as on P. 

 aurelia further evidence that the 

 new species is a Paramecium! 



From the foregoing description of 

 the structure and life history of P. 

 calkinsi it is apparent that this 



24 I am indebted to Miss Hope Spencer of 

 the Osborn Laboratory for assistance in carry- 

 ing out this work. 



26 Woodruff and Baitsell, "Rhythms in the 

 Reproductive Activity of Infusoria," Jour. 

 Exper. Zoo/., n, 1911. Woodruff and Erd- 

 mann, "A Normal Periodic Reorganization 

 Process without Cell fusion in Paramecium," 

 Jour. Exper. Zool., 17, 1914. Erdmann and 

 Woodruff, "The Periodic Reorganization 

 Piocess in Paramecium caudaliim," Jour. 

 Exper. Zool., 2'-, 1916. 



o _ 





~ o 



