THE SENSORY RESPONSES OF CHITON 243 



N/112 Edge of the foot fails; the palp is sensitive on its 

 edge and bends first toward, then away from, the 

 stimulus. 



N/160 Faint responses from the mouth region. 



From one animal, considerably more sensitive than the rest, faint 

 mouth-region responses were also obtained at dilutions N/224 and 

 N/256; this was very exceptional. 



KOH: The dilutions tabulated are here only approximate, owing to 

 the precipitation of calcium and magnesium hydrates at concentra- 

 tions above 0.012 N ± KOH (Haas, '16). 



N/10 Reactions produced on all parts except upon the ven- 

 tral surface of the girdle (mantle edge). 



N/50 to N/125 Same. 



N/250 to N/375 The edge of the foot is but slightly sensitive. 



N/500 No responses from the foot; reaction at the mouth 

 just perceptible; gill responses of fair intensity. 

 HCl: N/10 No reaction from the ventral surface of the mantle 

 edge. 



N/50 to N/425 — responses from all parts, save the mantle 

 edge. 



N/500 No reactions from the foot; very faint responses from 

 the mouth; gills respond more weakly still, but with 

 fair sensitivity. 



Several organic acids were also tested. At M/10 concentration, in 

 rain water, tannic, malic, lactic and acetic acids produced reactions 

 from all parts, including the mantle edge. M/lOO solutions of the same 

 acids made up in sea-water also induced responses, but not from the 

 mantle edge; these acids were compared by noting the 'recovery time' 

 of the gills when stimulated with them (as in the case of salts); the 

 measurements obtained were: 



Tannic, 35 sec. 

 Mahc, 20 sec. 

 Lactic, 12 sec. 

 Acetic, 8 sec. 



Picric acid: made up in sea-water, produced very powerful reactions 

 everywhere, at concentrations above M/150. 



M/250 Responses of the same character, but weaker. 

 M/500 to M/750 The edge of the mantle fails. 

 M/1000 The foot still sensitive, especially along its periphery. 

 M/1200 Gills fail; foot and mouth give good reactions. 

 M/1500 Foot fails; mouth alone responds, but smoothly and 

 evenly. 



