Yerkes, The Sense of Hearing in Frogs. 



297 



floating upward by the attachment of a one gram weight. The 

 two stimuli were given by means of the hand key, K. In all 

 cases the auditory stimulus was the sound of an electric bell, B^ 

 suspended above the water in such a way that its vibrations 

 could not be transmitted either to the aquarium or the frog 

 holder. Precautions were taken to exclude also the influence 

 of visual stimuli. 



During the month of December, 1904, ten green frogs 

 were tested with this apparatus and it was found, contrary to 

 the expectations aroused by previous results, that the females 



Fig. 7. Auditory apparatus for testing hearing in air and in water. A^ 

 aquarium ; B, electric bell ; T, tactual stimulus apparatus ; K, hand-key for gir- 

 ing stimuli ; tc, weight to hold leg. 



reacted far more uniformly and vigorously to sounds than the 

 males. Indeed the irregularity of response and irresponsive- 

 ness of the males were so marked that it was seldom possible 

 to get more than two or three pairs of reactions in series. For 

 this reason it has been impossible to present averages for the 

 males. The females reacted with a fair degree of regularity, 

 but with notning like the vigor and uniformity which character- 

 ized the reactions of animals tested in April and May. Evi- 



