REPKODUCTION OF THE HYPOTRICHOUS INFUSORIA 73 



tract medium until February 24, 1911, when it died out at the 

 403rd generation, following an epidemic of conjugation. Culture 

 'Sbh was started November 23, 1910, from culture Sb when it was 

 at the 150th generation and was carried on a hay infusion medium 

 until August 15, 1911, when it died out at the 572nd generation. 

 Culture Sbhb was started from culture Shb March 3, 1911, at the 

 360th generation and was carried on the beef medium until July 

 5, 1911, when it died out at the 507th generation, following an 

 epidemic of conjugation. Graphs showing the life history of each 

 culture have been plotted by averaging the divisions in the four 

 lines of each culture for ten day periods. 



4. In the culture kept on the hay medium conjugation never oc- 

 curred and abnormal or degenerating animals did not appear, but 

 after a gradual decline in the fission rate the culture finally died 

 out. It is not believed that this result was due to the ending of any 

 definite life-cycle but rather to the failure of the hay medium to 

 furnish an environment which was exactly suitable for the contin- 

 ued existence of this species. This view is substantiated by work 

 to be reported in a subsequent paper. 



5. In both of the cultures kept on the beef medium an epidemic 

 of iiifertile conjugation occurred, and within three weeks after its 

 appearance all the non-conjugants in both of the cultures died, 



6. Careful study of the living and prepared material shows a 

 normal morphological condition of the animals at the time of con- 

 jugation, but shortly after its appearance degenerative changes 

 were evide.it. 



7. All ex-conjugants passed through degenerative stages which 

 ended in their death within forty-eight hours after separation with- 

 out division. 



8. A study of the prepared material shows that the micronuclei 

 are present in non-conjugants, conjugants and ex-conjugants at all 

 stages. 



9. There is no evidence to show that the infertility of conjuga- 

 tion was due to any abnormal conditions previous to, or during, 

 conjugation. 



10. The experiments show conclusively, it is believed, that con- 

 jugation is induced by external conditions affecting the organism. 



