LIFE HISTORY OF DIDINIUM 233 



division rate, I have worked them out on this basis. The fluc- 

 tuations of the appetite curve follow closely those of the division 

 rate and both are correlated with the fluctuations in the curve 

 of encystment. When the latter reaches 100 per cent both 

 division-rate and appetite-rate fall to zero. The over-lapping 

 at this period (Dec. 25 to Dec. 30) is due to the fact that Para- 

 mecium may be eaten prior to encystment but without division 

 of Didinium. 



TJie second cycle {December 28 to March 5): Individual X » 



All the living material of Didinium in culture and stock dishes 

 became encysted during the period beginning December 25. The 

 race was recovered from encystment December 28, by pouring 

 off the old water and adding fresh water and Paramecium to a 

 Syracuse dish in which stock material of the X series had encysted 

 the week before. The division rate immediately indicated a 

 renewal of vitality, giving an average for the first 20 days of 2.01 

 divisions per day. It then fell to 1.76 for the second 20 days 

 and to 1.25 for the third 20 days. In the last 5-day period 

 (February 28 to March 4) it averaged only 0.52 divisions per 

 day, after which all culture material and stock material en- 

 cysted (chart B). The race passed through 148 generations 

 during this cycle, or 279 generations since the culture experiments 

 started. 



The rate of encystment began at 16 per cent for the first 5-day 

 period but quickly fell and remained low during the first 40 days, 

 after which it maintained an average of about 17 per cent until 

 all individuals became encysted (chart B, bottom). 



An interesting feature of this second cycle was the increase 

 in the average death rate over the first cycle. The average 

 death rate for the entire first cycle was 1.8 per cent and for the 

 entire second cycle it rose to 7 per cent. When we consider the 

 relative infrequency of death of the individuals in culture this 

 phenomenon becomes significant (chart B, top). 



As in the first cycle, the curve for appetite closely follows the 

 curve of reproduction (chart B, dotted line). 



