OLFACTORY REACTIONS IN AMPHIBIANS 645 



The conclusion reached from these experiments as described 

 for the different broods of tadpoles is that the presence of the 

 nasal plug is effect ve in inhibiting any stimulus coming to the 



sense organ and consequently no corresponding reaction follows. 



* 



DISCUSSION 



1, Toads 



In its method of obtaining food the toad seems to respond 

 to the visual stimulus entirely. This stimulus is apparently 

 effective only when it involves motion. It is not always fol- 

 lowed by perfect reaction, for substances inappropriate as food 

 are often taken accidentally. Rejection of such material occurs 

 in compliance with mechanical or tactile stimulation. 



Nor does the gustatory function appear to be of any im- 

 portance in feeding. Gaupp ('04) does not consider the function 

 of the epithelial endplates of the mouth cavity to be established. 

 He refers to Bethe as bringing forward the best evidence favoring 

 them as tactile organs. It has been shown that strong solutions 

 of picric or acetic acid applied to the epithelium of the mouth 

 cavity will cause appropriate motor activity. Such reactions 

 take place without reference to the point of application of the 

 acid, whether this be in regions supplied with endplates or de- 

 void of them. The latent period between stimulus and reaction 

 is of appreciable duration. 



These considerations speak against the belief that these organs 

 are gustatory in function. 



Until the contrary is proven, the similarity of food materials 

 of frogs and toads argue for similarity in structure of the epi- 

 thelium of the mouth. Observations and feeding experiments 

 tend to confirm this view. Food does not remain in the mouth 

 cavity any great length of time. Deglutition follows almost 

 instantly, and therefore the sense of taste would be of minor 

 importance. Under certain conditions regurgitation may occur. 

 If substances disagreeable to taste are taken into the mouth the 

 animals might be expected to resort to this expediency more 

 often. 



