278 'Journal of Co7nparative Neurology and Psychology. 



between the two sets of apertures f)reventing diffusion of the stimulus 

 from one set to the other. 



Regions Tested. — ^With each solution used, approximately fifty 

 places on the body were tested at each concentration used, and the 

 time of reaction always recorded with a stop watch. These regions 

 included the mouth, nostrils, spiracles, anus, claspers, and selected 

 places on the fins, dorsal, lateral, and ventral surfaces of the fish. For 

 the location of these points see figures 1 and 2. 



Reactions Obtained. 

 The reactions obtained varied according to the part of the body 

 stimulated, as follows: Stimulation of the mouth or spiracles is fol- 

 lowed by one or more violent gulps, accompanied, of course, by a 

 quick ejection of water through the branchial openings. A more rapid 

 respiration for a greater or less length of time, depending on the 

 stimulus, follows this. This is the only reaction secured by chemi- 

 cal stimulation of the mouth and spiracles, and it is secured by stimu- 

 lus of no other region. When the nostrils are stimulated by any of 

 the substances used, the reaction is likewise very characteristic. It 

 consists essentially of a very quick jerk of the head. This reaction is 

 likewise secured by stimulation of no other region. In the case of the 

 paired fins the characteristic reaction is a quick movement of the 

 fins, usually of a vibratory type. Often, particularly if the stimulus 

 is weak, the first reaction is a turning or movement of the whole fin 

 toward the stimulus, occasionally away from it, followed usually by 

 vibration of the fin. With the median fins the reactions are very 

 similar. The more usual reaction, however, begins with the movement 

 of the fin toward the stimulus. Often the small caudal finlets of the 

 median dorsals and the anal fin will react by a rapid vibration, even 

 though that part of the fin is not stimulated. If this reaction occurs, 

 it usually begins by a quick movement of the finlet toward the stimu- 

 lus, more rarely away from it. When the finlet of either the anal or 

 second dorsal fin takes j^art in the reaction, the other does also, so 

 that the action of the two is simultaneous and in the same direction. 

 When the caudal fin is stimulated, the reaction consists in a rather 

 slow sidewise movement of the tail either toward, or away from, the 



