AXIAL GRADIENT IX CILIATE IXFUSORIA. 51 



the rate of reaction sufficiently high to bring about the rapid 

 change. In higher concentrations the special susceptibility 

 may appear in both vacuolar regions, but even in such cases the 

 swelling usually appears earlier or is of larger size in the anterior 

 region. In short the facts indicate that the two vacuolar regions 

 of Paramcecium are more or less definitely localized regions of 

 relatively high rate of metabolism or more specifically of res- 

 piration and, furthermore, that the rate in the anterior vacuolar 

 region is higher than that in the posterior. 



The lower susceptibility of the posterior vacuolar region to 

 KCN and the lower rate of pulsation of the posterior vacuole 

 in normal living animals suggest the existence of an axial gradient 

 in rate of metabolism, and in the death and disintegration of the 

 body in general this gradient appears as has been shown. When 

 the disintegrative change begins to spread from the vacuolar 

 region the anterior end of the body is attacked first and from 

 this end the process of disintegration spreads downward to the 

 posterior end. The differences in susceptibility along the axis 

 are not as great as the differences between peristome and other 

 regions in Stentor and Vorticella, in other words the axial gradient 

 in rate is less steep in Paramcecium than in those forms. 



A general relation seems to exist between the character of the 

 gradient and the degree of morphological and physiological 

 "cephalization" in these different forms. In Paramcecium the 

 gradient is comparatively slight and apparently uniform except 

 for the vacuolar regions. In Stylonychia and En plot es the gra- 

 dient is steeper, i. e., the differences are greater but here also 

 it is uniform or nearly so. In Stentor a distinct gradient, steeper 

 in the more anterior regions than that in Paramcecium, extends 

 throughout the length of the body, but the peristome region is 

 distinctly marked off from other parts by its higher rate, i. e., 

 the gradient from the peristome region to other parts is steeper 

 than the gradient in other regions. And finally in Vorticella and 

 Carchesium the gradient between peristome and other regions 

 is steep as in Stentor but in other parts of the body the gradient 

 is slight. When we compare these facts with the differences in 

 morphology and behavior of these different species and of the 

 different regions of the body in each the general parallelism 



