28 IOWA STUDIES IN NATURAL HISTORY 
depends less on their capacity to escape their enemies by imme- 
diate effort than on the protection afforded by the environment. 
Consequently there is a priori no ground for the assumption 
that these animals possess associative memory or the capacity to 
learn by repeated experience to a greater degree than certain of 
the fish, even though the latter possess a relatively less complex 
nervous mechanism. 
Neither is there any ground for the assumption that the Uro- 
dela and Anura possess associative memory in like degree. Fur- 
thermore, the animals used in this study had not yet attained 
their adult condition. | Consequently, direct comparison of 
their achievements with those of the animals used in the studies 
referred to above would have little significance. 
One of the most important factors in studies of this character 
is the stimulus employed. It must be one which will insure 
more or less continuous effort on the part of the animal until 
the object is reached. Some of the lower vertebrates, when 
hungry, are stimulated strongly by the presence of food. Such 
animals, under proper conditions, make a more or less continu- 
ous effort to find the way through a simple maze in order to se- 
cure food. In such eases food is a very satisfactory stimulus. 
The larvae of Ambystoma are not sufficiently strongly stimulat- 
ed by the presence of food, even when hungry, to insure a sus- 
tained effort to secure it. However, they react strongly to in- 
tense light. When exposed to direct sunlight they seek any 
available shaded area. They are not always as persistent in 
their efforts to escape the direct rays of the sun as the ex- 
perimenter might wish. Nevertheless, direct sunlight probably 
is the best stimulus available for studies of this character on 
the larvae of Ambystoma. 
A simple maze (fig. 1), similar to those used by Thorndike 
and Churchill, was arranged in an aquarium (62x21x23 em.) 
with metal walls. In the bottom of the aquarium was a bed 
of sand approximately 4 em. in depth. The water over the sand 
was approximately 6 em. in depth. The aquarium was placed 
in direct sunlight so that the entire area of the water except 
that which fell within the shadow of the end wall toward the 
sun was exposed to the sun’s rays. 
Animals which react negatively to intense light commonly re- 
