2IO C. M. CHILD AND L. H. HYMAN. 



acropetally, i. e., the susceptibility of these regions was like that 

 of many other detached animals. 



Figs. 80 and 81 show the course of disintegration in an animal 

 which contained a recently ingested chironomid larva when it 

 was placed in cyanide, but disgorged the larva within the first 

 five minutes. Although disintegration did not begin until an 

 hour later, the region of the body in which the larva had been 

 began to disintegrate as soon as the tentacles (Fig. 80) and was 

 completely disintegrated before any other part of the stalk or 

 body except the most apical region (Fig. 81). 



These and numerous other similar cases observed indicate that 

 the activity of the entoderm in digestion extends to the ectoderm 

 of the region concerned. The relations already described be- 

 tween susceptibility and muscular contraction indicate that more 

 or less transmission or irradiation of local excitations inducing 

 contraction occurs, and these cases of high susceptibility asso- 

 ciated with digestive activity indicate an irradiation to the ecto- 

 derm of the entodermal excitation produced by food. Probably 

 no excitation is sharply localized in hydra. 



THE COLOR GRADIENTS IN POTASSIUM PERMANGANATE. 



It has been found by one of us that the axial gradients in phys- 

 iological condition in various plants and animals can be demon- 

 strated as color gradients through the reduction of potassium 

 permanganate to MnO2 by the living protoplasm, the regions of 

 high susceptibility and high oxidation rate reducing the perman- 

 ganate more rapidly and so being stained more rapidly or more 

 deeply by the MnC>2 (Child, '19). Some observations with per- 

 manganate have been made on all three species of hydra but the 

 agent produces a great irritation even in very low concentrations 

 (m/5O,ooo) and the resulting contraction is so extreme that it is 

 difficult to distinguish anything more than the general color 

 gradations in full grown animals and later bud stages. 



The earlier bud stages which possess little or no contractility 

 show a distinct basipetal color gradient in permanganate, cor- 

 responding to the primary susceptibility gradient. In the ten- 

 tacles also the color gradient is basipetal like the susceptibility 

 gradient. Fully developed animals almost invariably detach 



