50 GEORGE ALFRED BAITSELL 



To summarize briefly, then it has been shown by a number of 

 investigators working on several species of Infusoria that Maupas 

 was incorrect in asserting (1) that the Infusoria have a definite 

 hfe cycle in which can be distinguished a period of sexual maturity 

 during which time conjugation will be fertile and if conjugation 

 does not take place, a resulting period of 'senile degeneration' 

 finally terminating with the death of the organism after a certain 

 number of generations, (2) that conjugation, in order to be fertile, 

 must be between gametes of diverse ancestry. Finally, the work 

 of Woodruff with Paramaecium aurelia has shown that it is 

 possible to breed this organism indefinitely without conjugation 

 or artificial stimulation. 



Inasmuch as Stylonychia pustulata has been shown to be a spe- 

 cies well adapted to the treatment demanded in laboratory cul- 

 tures and also because some of Maupas' conclusions which have 

 been shown not to hold for other of the Infusoria have not been 

 re-investigated in the species which he used, it was decided to 

 make use of this Species in these experiments. In the present 

 paper is presented a study of the following points: 



1. The life history of Stylonychia pustulata when bred on a 

 'constant' culture medium of beef extract and a culture medium 

 of hay infusion. 



2. The morphological and physiological changes during the 

 life of the organism when bred on these culture media. 



3. The relation of conjugation to the environment of the or- 

 ganisms. 



4. The effect of conjugation between closely related individu- 

 als which have had an identical environmental history. 



The writer is glad of the opportunity to express his great indebt- 

 edness to Professor Lorande L. Woodruff not only for suggesting 

 the problem but also for his advice and helpful criticism during the 

 entire course of the work. 



