228 INTELLIGENCE IN LOWER VERTEBRATES 
limited. Abbot placed a large fly on a piece of thin mica 
surrounded by needles so that the frog would be pricked 
in its efforts to seize it. This did not prevent the creature 
from snapping at the fly indefinitely. “In one instance 
the frog, which had been fasting for seventy-two hours, 
continued to snap at the needle protected fly until it had 
entirely skinned its upper jaw.” This convinced Abbot 
that “the wits of a frog were too limited to be demon- 
strated.’’ Knauer found that frogs would snap at worms on 
the other side of a glass plate and persist in doing so at inter- 
vals all day without learning that their attempts were futile. 
On the other hand, several cases are recorded of frogs as 
well as toads being trained to come for food. Toads often 
occupy for a long time a particular retreat to which they 
return after making their nocturnal tours, thus showing 
that they have a memory for location. Yerkes in his stud- 
ies of habit formation in frogs finds that frogs learn very 
slowly. In the experiments performed the frogs were placed 
in a long box furnished with a tank filled with water at one 
end and divided so that the frog would have to take a cer- 
tain course from the point of entrance to get into the tank. 
The labyrinth employed was very simple, but it took from 
50 to 100 trials for a frog to learn to avoid the closed pas- 
sages and to reach the water by the most direct route. The 
associations once formed were found to persist for over a 
month. 
Schaeffer’s recent experiments on habit formation in 
frogs have shown that frogs may learn to avoid disagree- 
able objects after a very few trials. When offered hairy 
caterpillars the frogs would eagerly snap at them and then 
quickly eject them from the mouth. After from four to 
seven such experiences the frogs came to leave the cater- 
pillars alone. 
