44 



C. M. CHILD. 



In all four species examined the peristome region is very 

 evidently more susceptible to the reagent than other parts. In 

 the remainder of the body the death changes do progress from 

 the oral to the aboral end, but their progress is much more rapid 

 than in Stentor. In KCN o.oi w. disintegration is completed 

 within 5-10 seconds after the pause following peristome disin- 

 tegration. In these forms then the axial gradient consists first 



in a marked decrease in susceptibility from the peristome region 

 to more aboral regions and a slight decrease in the rest of the 

 body from the oral to the aboral end. 



V. HOLOTRICHA. 



Paramcecium is not very susceptible to KCN, but the individual 

 differences in resistance are considerable. In KCN o.oi m. with 

 water-temperature 22-25 C. average survival time of animals 

 from one culture was six or seven hours, but some animals die 

 after two or three hours and some live eight or ten hours. More- 

 over, different cultures differ very considerably in resistance to 

 cyanide. 



When the animals are placed in KCN they at once begin to 

 swim backward. This continues for a period varying from a 

 few minutes to half an hour or in some cases longer. Gradually 

 the backward movement becomes less and less marked until the 

 animal is simply revolving and then sooner or later it begins to 

 swim forward once more and continues until it dies. 



In KCN o.oi m. the disintegration changes begin in the great 



