60 IOWA STUDIES IN NATURAL HISTORY 
If they could be swallowed without difficulty they were prompt- 
ly swallowed, otherwise they were discarded after an attempt to 
swallow them. These animals would seize and swallow pledg- 
ets of cotton quite as promptly as pieces of meat regardless 
of whether or not the pieces of meat and the pledgets of cot- 
ton were concealed in packets which were similar in appear- 
ance. Obviously these animals did not discriminate between 
food and inedible objects. Inasmuch as the de-eyed animals 
did discriminate between edible and inedible objects the con- 
clusion that such discrimination is accomplished primarily by 
the olfactory sense is warranted. 
Attempts to demonstrate a sense of taste in these animals 
resulted negatively. Obviously it would be quite impossible 
to differentiate between the manifestations of an olfactory and 
a gustatory sense in normal animals. However, if animals in 
which the olfactory nerves are severed should react to the fluid 
extracts of food introduced into their mouths such reactions 
might be interpreted as the manifestations of a gustatory sense. 
Accordingly aqueous extracts of frog’s meat and crayfish’s 
meat were introduced into the mouths of the animals whose 
olfactory nerves were severed, but no reactions were elicited. 
The results of the foregoing experiments on Ambystoma tigrin- 
um, in so far as they bear upon the relative importance of the 
sense of sight and the olfactory sense in the feeding reactions, 
agree in general with the results of Copeland’s experiments on 
Diemyctylus viridescens. 
SUMMARY 
The typical response of the larvae of Ambystoma tigrinum to 
the presence of food consists in an ‘‘approaching’’ and a ‘‘seiz- 
ing’’ reaction. Young adults frequently exhibit also a ‘‘nos- 
ing’’ reaction. The ‘‘approaching’’ reaction is commonly a vis- 
ual response. © The ‘‘nosing’’ and ‘‘seizing’’ reactions, except 
when the latter follows the ‘‘approaching’’ reaction more or less 
spontaneously, involve the olfactory sense. 
Moving objects are detected and pursued more promptly than 
objects which are not in motion. 
In the absence of sight food is detected by the sense of smell. 
Discrimination between edible and inedible objects also depends 
- on the olfactory sense. 
