THE GREEN FROG 337 



the country knows of the difficulty of approaching these alert 

 creatures, and he knows, too, how to capture them by dang- 

 ling a hook with a piece of red flannel in front of them. 

 Even if well fed the frog seems to find the moving object irre- 

 sistible, and seizes it with wide-open mouth. The tongue is 

 covered with a sticky substance, and can be swiftly extended 

 with unerring aim to a distance of several inches. 



While the frog depends very largely on the sense of sight 

 to warn it of approaching enemies or enable it to distin- 

 guish food, the sense of hearing is also of considerable value. 

 Dr. R. M. Yerkes, of Harvard University, who has studied 

 the sense of hearing in frogs both in the laboratory and in 

 the field, says that he is convinced that sounds which are of 

 importance in the life of the animal, as the splash made by 

 a frog jumping into the water, are not only heard, but that 

 such sounds serve to put other frogs on their guard. The 

 croaking of male frogs in the spring is undoubtedly heard 

 by the female, and serves to make mating more certain. 



The observer just quoted does not give the green frog 

 credit for much intelligence, as his experiments seem to 

 show that nearly all the frog's actions are repeated with 

 machine-like accuracy, and new habits are learned very 

 slowly. He is inclined to think that even the perch learns 

 more rapidly than the frog. He also notes that the frog is 

 very timid, and that fright tends to lengthen the process of 

 learning. 



When suddenly touched, the frog may do one of several 

 things: it may jump, using the strong hind legs sometimes 

 with force enough to carry it several feet ; it may remain 

 perfectly quiet ; or it may crouch with its head close to 

 the ground, at the same time puffing itself out. This last 

 action, Dr. Yerkes has noticed, more often takes place when 

 the animal is touched in front, and is probably useful to 

 render seizure difficult, or to prevent it altogether. If the frog 



