22O BARBARA LEE LUND. 



TABLE IV. 



Didinium. 



A. Time after division when the sisters were killed in iV/2O KCN. One of 

 them had been starving in tap water, the other feeding on Paramecia in tap water. 

 The temperature for this experiment was between 23 and 24 C. throughout, 

 with the exception of the 12-hour lot when the temperature went down to 19 C- 

 This accounts for the longer survival time in that case. 



B and C are self explanatory, each number representing an average of 30 

 individuals. 



D. Difference between the two preceding figures in the same column. That is- 

 each number represents the average difference between 30 starved and 30 fed 

 Didinia sisters. 



increasing difference (Fig. 2, curve D) up to the fourth hour due 

 entirely to the fact that one sister has eaten while the other has 

 not; or do the sisters, presumably identical at the time of 

 separation, gradually diverge as a result of differing rates of 

 maturity, apart from effects of nutrition, so that even though 

 subjected to the same conditions they would show different 

 degrees of resistance as time went on? 



Experiment V. To answer this question an experiment was 

 carried out in the usual way, the dividing animals being isolated 

 and killed with KCN. I found, however, that the concentration 

 of KCN I had previously used did not bring out the small dif- 

 ferences in survival time as well in this case where the sisters were 

 in the same medium and both were without food, as a weaker 

 solution. Thirty pairs or sixty individuals were killed at the 

 end of each period of >, I, 2, 3, 4, 5, 6, 7, 8, 9, 12, 19 and 24 

 hours after division. Since there was no difference in appearance 

 or in previous treatment of the sisters I arbitrarily placed the 

 survival times of the animals which died first in one column, and 

 that of their more resistant sisters in another, took an average 

 of the thirty individuals in each case, and have given in Table V. 



