The Life History of Tillina Magna 403 



the end. The sudden drop at the last period, and the following 

 death of the culture was unexpected, and cannot be explained. 

 In the ninth period the division rate averaged 1.8 per day, then 

 suddenly many began to encyst, and the division rate fell to i per 

 day. Beef extract, alcohol, K^HPO^, and KCl were used as 

 stimulants, but with no effect, and the cultures died out March 

 I, when A2, the last one to divide, had been encysted for twelve 

 days. The stock material was low, otherwise I think the culture 

 might have been saved. The same sudden drop in the division 

 rate, near the end of the life history, has been noted by Maupas 

 in his culture of Stylonychia, and by Woodruff in his culture of 

 Gastrostyla steinii. In each case a period of comparatively high 

 division rate preceded the sudden death. 



The B culture was started at the same time as the A culture, 

 but from different stock. This culture as a whole was carried 

 through 405 days, a period of thirteen months, during which it 

 passed through 548 generations. 



The main or control culture, consisting of four lines, Bl, B2, 

 B3, B4, lived through 403 generations during 250 days. These 

 lines thus designated were not stimulated at any time in order that 

 the effects of stimulation in the other lines might be more apparent 

 upon comparison. Diagram III shows the life history of this 

 culture. The curve is a normal one, falling naturally into the 

 rhythmical periods already mentioned. There is a gradual de- 

 crease in vitality from beginning to end. At the 24th period the 

 rate of division increased to some extent, chang ng from an aver- 

 age of .87 to 1.37 divisions per day. All the lines increased rap- 

 idly in numbers during this period; this was due undoubtedly to 

 the unusual hot weather. At the end of this period the lines were 

 weak, and all save two stimulated lines, died, in spite of extreme 

 efforts to save them. 



At the beginning of the 12th period, at the time of the death of 

 the A culture, although the main lines of the B series were divid- 

 ing on the average of two divisions a day, it was thought best to 

 try the effect of stimulants on the division rate as previous investi- 

 gators had found that certain stimulants would increase the vital- 

 ity of the protoplasm, and enable it to renew its life process in 



