REACTIONS OF A. TIGRINUM 277 



DISCUSSION 



The observations upon the operated larvae show that A. 

 tigrinum possesses an olfactory sense. They also indicate the 

 relative importance of the senses of sight and smell. Sight is 

 undoubtedly the predominant sense in the obtaining of food, 

 although it is rather interesting to observe that under conditions 

 of paucity of food the animals in which the organ of sight has 

 been removed, long before it could possibly function, have a 

 more highly developed sensitivity toward objects giving an 

 olfactory stimulus than do the normal animals. There seems 

 to be a dominance of one sense over the other, this dominance 

 being clearly detrimental to the animal under adverse conditions. 

 This same condition is demonstrated in the observations upon the 

 adult forms. A comparison between the ability of the blinded 

 adults to obtain food and of normal individuals in the dark room 

 is striking. Blinded adults give a positive reaction to olfactory 

 stimulation in practically the same time as normal animals in 

 the light. Risser has noted that there is what he has termed an 

 inhibitory effect of the eyes over the nose in the toad. It is 

 true that an animal possessing sight cannot accommodate it- 

 self to olfactory stimulation under conditions of darkness in the 

 same time that blinded animals which have become accustomed 

 to obtain food substances without the intermediation of sight can 

 do so. 



The factor of taste and its relation to the problem must be 

 considered. Although the animals are no e -stopped (tables 1, 

 series 4; 2, series 2; and 3, series 2), the organs of taste are un- 

 disturbed by this procedure. Water currents are passing in and 

 out of the animal's mouth and some of the diffusing substance 

 should come in contact with the taste buds. If the taste buds 

 are responsible for the reaction, there should be a reaction even 

 in nose-stopped animals. This is not found. In this case, how- 

 ever, the eye is a considerable factor, as is shown by the reaction 

 elicited by moving objects. In the series with eyes removed and 

 the nasal passages closed (tables 1, series 6; 2, series 4; and 3, 

 series 4) there is no reaction to any stimulus applied. The sense 

 of taste, therefore, can be regarded as a negligible factor. 



