Yerkes, The Sense of Hearing in Frogs. 



285 



size; in case of two individuals 6.5 cm. the measurement of the 

 male was 7.5 mm., that of the female 6.0 mm.; the tympanum 

 of a male 8.8 cm. long measured 11. 5 mm., that of a female 

 9.0 cm. long, 9 mm. In almost all cases the difference in the 

 size is so marked as to be noticeable to a casual observer. 



J^ig. J. Photograph of green frogs (Rana ciatnitans), male on the right, 

 female on the left. To show the difference in size of tympana. 



J. Problems. The purpose of the investigation of which 

 this paper gives an account was the study of the influence of 

 sounds on the reactions of the frog. The definite questions for 

 which answers were sought are four: i. Do frogs react to 

 sound? 2. Do they hear? 3. If so, what sounds are heard? 

 4. Under what conditions do reactions to sounds occur ? 

 No attempt was made to localize the function of audition within 

 the labyrinth organs, for the problems of research concern be- 

 havior rather than the functions of special organs. 



In studies of this sort it is to be remembered that normal 

 behavior can not be studied by vivisectional methods. Oper- 



