248 LESLIE B. AREY AND W. J. CROZIER 



trolytes of the sugar type. The order of kation stimulating 

 efficiency for the alkah chlorides, 



K > NH4 > Li > Na, 



is that found in the sensory activation of Balanoglossus (Cro- 

 zier, '15 a), Ascidia (Hecht, '18), Chromodoris (Arey), and 

 other marine animals, and is in accord with the general order of 

 action of these ions upon various protoplasmic processes. The 

 anion order, 



CI > NO3 > Br > I, 



does not agree with that determined by Hecht ('18) for Ascidia; 

 but the methods of experimentation were in the two cases quite 

 different, in the tests with Ascidia the method of limiting effec- 

 tive dilutions being employed and the salts being dissolved in 

 sea-water. For Synaptula (Olmsted, '17 b), the order CI < 

 Br < I, as in Ascidia, was found, by the same general method. 

 Each of these anion series has its counterpart in other salt actions 

 (Hober, '14), but why they should be reciprocal is not altogether 

 clear, particularly since the kation orders obtained by these 

 respectively different methods are in agreement. In Chiton, 

 general chemical excitation is primarily an affair of the kation. 



The minimal concentrations of different electrolytes which are 

 effective in the excitation of different regions of Chiton appear 

 to be as follows (in sea-water solutions) : 



The three organic acids we employed stimulated according to 

 the following order of efficiency: 



Mafic > lactic > acetic (M/lOO in sea-water). This order 

 indicates that for Chiton lactic acid is less efficient as a sensory 

 excitant than malic, which is not the sequence shown (Crozier, 

 '16 a) by the earthworm's reactions, nor in the penetration of 

 tissues by these acids, but does correspond with the respective 

 magnitudes of acid strength. Since the solutions were made up 

 in sea-water, much emphasis cannot be placed on this point. 



The very general nature of Chiton's sensitivity, involving 

 excitation by a great variety of materials in solution, adheres 

 nevertheless to the rules already available in the activation of 



