THE INTELLIGENCE OF THE FROG 



355 



water if they can perceive it, even when they cannot get 

 into it, although they may easily reach another body of 

 water at a somewhat greater distance. Abbott buried a 

 pail of water to the brim in dry ground within fifty yards of 

 a running brook, and covered it with a sieve. He then 

 " took seven frogs of three species and placed them on the 



FIG. 94. — Labyrinth used in studying the formation of habits by the frog. 

 From A the frog enters at E. G, glass plate ; P, partition ; P, red surface ; 

 W, white surface ; T, tank. (After Yerkes.) 



sieve, which was about half an inch above the surface of the 

 water. Here five of them remained during the whole day, 

 exposed to the glare and heat of a cloudless summer day. 

 The evaporation from the water beneath barely kept them 

 alive ; and yet within so short a distance was a running 

 brook, with all the attractive features of ideal frog life." 

 An animal like a dog, after finding that it could not get 

 at the water in the pail, would waste little time in making 

 for the brook ; but the frog is so limited in its resources, 

 that such a course is out of reach of its powers. 



Yerkes has studied the power of forming associations in 

 frogs, and has come to the conclusion that their learning is 

 slow, but that habits once formed are hard to change. The 

 frogs experimented with were placed in a labyrinth (Fig. 94) 

 formed by a box 72 cm. long, 28 cm. wide, and 28 cm. deep. 

 The frog enters the box through a small opening at one end 

 A. At the other end of the box an opening at one side leads 



