Introduction 



the mouth widely opened. It is given only when the frog is 

 injured by an enemy or is in a state of great fear. The cry ex- 

 presses distress in large measure, and must imply to the listen- 

 ing frogs the presence of great danger. 



The frog's ear has the functions of balance and orientation 

 as well as the sense of hearing. 1 Sometimes in spring, after the 

 breeding season, a frog is found that has the ear badly injured. 

 Such a frog keeps the head lowered on the wounded side. It 

 cannot progress directly, but moves in a circle instead. The auto- 

 matic action of the frog's ear in the work of orientation is inter- 

 estingly seen when we move a frog in its aquarium or moss gar- 

 den from one part of the room to another; or when we walk 

 from one place in the house to another with a toad or frog sitting 

 on some support which is carried in the hand. At each corner, 

 even at the slightest change in course, the frog turns its head to 

 adjust itself to the new direction. 



Sight and hearing are correlated senses, serving in the cap- 

 ture of food and the escape of enemies. The sense of sight and 

 the temperature sense are correlated in receiving stimuli which 

 result in various protective actions. In normal temperature, 

 frogs are attracted by light and move towards it (positively pho- 

 totactic). That a frog jumps into the water when frightened, in- 

 stead of landwards, probably illustrates the fact that a frog moves 

 toward the stronger light or more brightly illuminated surface. 



Frogs in captivity constantly illustrate this relation to light. 

 In trying to escape from an opaque pail, they leap upwards; in 

 a glass aquarium they struggle to get directly through the glass 

 (even when the glass is covered with'white paper so that they 

 cannot see through it). A tree frog will try for hours to get out 

 at the upper end of a glass beaker turned upside down; darken 

 the upper part and the frog will go to the source of light below 

 and find the opening. A frog moves not only towards diffused 

 light but towards direct sunlight as well. However, it does not 

 remain in the sunlight, but takes a station near it, in diffused light 

 or shadow. 



Frogs do not distinguish between a lighted space and a white 

 solid. They will turn towards a white card or paper and try 



1 The static and acoustic functions lie in the labyrinth organs (connected with the tympanum by 

 means of the columella), since there is no organ of Corti, as in mammals. It is thought that the 

 papilla basilaris (the nerve end organ from which originates the organ of Corti in mammals) is the 



iv*rof f*r\Tie*fmt*fl \n tlif ar-midir- ( unr-t Jr\n 



most concerned in the acoustic function. 



32 



