SENSE OP SMELL IN DOGFISH. 



67 



Table 4.— Records from Three Dogfish under Successive Conditions, Normal, Left Nostril 



Occluded, and Both Nostrils Open. 



It is quite evident from an inspection of table 4 that the conditions recorded in 

 the preceding tables are not due to individual peculiarities on the part of the fish used; 

 that a given fish, which in finding its food normally turns as much to the right as to the 

 left, can be forced to assume either a predominantly right-handed or left-handed course 

 by occluding the appropriate nostril, and that after this treatment the same fish can 

 recover its normal methods of search by the liberation of both nostrils. It must also 

 be evident from the whole series of records that the dogfish does not run upon its food 

 by accident, but finds it in response to an influence more less directive in character. 



The consistent and striking circular courses that these fishes can be forced to assume 

 have, in my opinion, more than a superficial resemblance to the so-called circus move- 

 ments of the invertebrates. These movements are dependent on the differences of 

 intensity of stimulation on the two sides of the body and this explanation holds, I 

 believe, for the circular movements of the dogfish. When a dogfish first enters water 

 permeated with odorous material from its food, it invariably makes a quick turn with 

 its head which, if the conditions of the water have been disturbed by currents, is always 

 toward the bait. This movement is followed by other movements of a like kind whereby 

 the fish eventually reaches the bait. When the normal conditions of the fish are dis- 

 turbed by the complete occlusion of one nostril, the fish swims as though it were in 

 water that was highly charged with odorous particles on the side of its body correspond- 

 ing to the open nostril and devoid of these particles on the opposite side. The fish 

 therefore turns toward the side of the open nostril, but since, under the artificial con- 

 ditions of the experiments, this turn does not equalize the stimulus, the motion is con- 

 tinued and a circular form of locomotion results. Thus, in my opinion, the more or less 

 circular movements induced in a dogfish with an occluded nostril by an odorous bait 

 are to be explained upon the same basis as the circus movements of such invertebrates 

 as crustaceans, insects, etc. 



