INTELLIGENCE IN LOWER VERTEBRATES 229 
In another set of experiments frogs were offered earth- 
worms which had been dipped in chemicals. These worms 
were frequently snapped at and swallowed. The diet pro- 
duced in some cases symptoms of uneasiness and some of 
the frogs would avoid eating earthworms for several days 
afterward, although they would partake freely of other 
kinds of food. 
An apparatus was arranged so that the frogs would re- 
ceive an electric shock every time they snapped at a worm. 
These frogs would avoid food altogether for a few days 
after the shock. Whether an association was formed in 
this case, or whether the result is due simply to the per- 
sistance of the effect of the strong stimulus is uncertain. 
That the frogs learn to avoid certain kinds of food more 
quickly than they learn to follow a particular path may, 
as Schaeffer suggests, be due to the fact that the discrim- 
ination of food is so common an experience in the course 
of a frog’s daily life. The greater severity of the penalty 
for error may be also a factor. 
What has been written on intelligence of reptiles is for 
the most part in the form of scattered, casual observations. 
We have several records of the taming of different reptiles, 
of their following their keepers, their distinguishing between 
different persons, and their coming when called. Delboeuf 
kept two lizards in captivity and in time they became quite 
attached to their keeper. They would run to him from 
across the room when called and crawl upon his body in the 
hope of being fed. Each showed jealousy if any attention 
were paid to the other. 
Gilbert White in his Natural History of Selbourne gives 
an account of a tortoise which distinguished between dif- 
ferent persons and became much attached to an old lady so 
that “whenever the good old lady came in sight who had 
