The Life History of TiUina Magna 399 



approximately the same time. In the history of Colpoda cucullus, 

 division within the cysts may take place either by forming two, four 

 or eight individuals, by successive divisions, in a similar manner 

 to that observed in Tillina, or by forming as many as twenty or 

 more individuals simultaneously, a process of true sporulation. 

 An interesting question in regard to the reproductive cysts, is 

 the significance of single and double divisions forming two and 

 four individuals respectively. This was found to take place also 

 in Colpoda, but not in similarlyshaped cysts as in Tillina. Rhum- 

 bler describes the single divisions as taking place only in the oval 

 cysts, and even then, only very seldom. I have tried to find if 

 there is any relation between the number of single divisions and 

 the vitality of the protoplasm. Diagram I shows the number of 

 single and double divisions in the main B culture during a period 

 of eight months. At the beginning, when the vitality was high, 

 and the divisions frequent (e.g., periods 1-26) there are more 

 double divisions than single, while in some five-day periods there 

 were no single divisions at all (e.g., period 2, 6, 10, 21). As 

 the vitality decreased, the number of single divisions grew more 

 frequent (e.g., periods 28, 29, 31, 35, 36), and at the end of the 

 history, there were more single than double divisions (e.g., periods 

 42, 44, 46, 48-50). Thus the appearance of single divisions might 

 be considered an indication of low protoplasmic vitality. 



V CONJUGATION 



Although the life history of Tillina magna was carefully watched 

 throughout thirteen months, or through 546 generations, no con-, 

 jugations or indications of conjugations were observed. Calkins 

 ('04) was able to bring about conjugation at almost any period by 

 putting in small watch glasses, masses of paramecia that had col- 

 lected about the edge of the culture jar. Similar attempts were 

 made with Tillina, but with no results. Neither individuals of 

 the same nor individuals of different ancestry, starved or well 

 fed, gave any evidence of conjugation. The experiments of 

 Joukowsky ('98), and of WoodrufF('o5), show that many hypotrich- 

 ous ciliates do pass through many generations without conjuga- 

 tion. Joukowsky carried Pleurotricha lanceolata through 460 



