304 Journal of Comparative Neurology and Psychology. 



another stimulus, an auditory stimulus may either reinforce or 

 inhibit the reaction appropriate to that stimulus. What may 

 be called reinforcement-inhibition curves for auditory stimuli 

 are presented in this paper. 



4. The green frog responds to sounds made in the air 

 whether the tympana be in the air or in water. There is some 

 evidence that the influence of auditory stimuli is most 

 marked when the drum is half submerged in water. The influ- 

 ence of sounds upon tactual reactions is evident when the frog 

 is submerged in water to a depth of 4 cm. 



5. Sounds varying in pitch from those of 50 to 10,000 

 vibrations per second effect the frog. The most striking results 

 were obtained by the use of an electric bell with a metal gong. 

 With this sound in connection with a weak tactual stimulus a 

 maximum reaction of the leg may often be obtained even when 

 either stimulus alone causes no perceivable reaction. 



6. Sounds modify the reactions of the frog after tympana 

 and columellae are removed. Cutting of the eighth cranial 

 nerves causes disappearance of the influence of sound. It is 

 clear then that the reactions to sounds are really auditory reac- 

 tions and that the sense of hearing in the frog is fairly well 

 developed, although there is little evidence of such a sense in 

 the motor reactions of the animal. 



7. Those portions of this investigation which were carried 

 out in the spring months show marked influence of sounds for 

 both males and females, whereas experiments made during the 

 winter indicate a much diminished sensitiveness to auditory 

 stimuli in both sexes, but especially in the male. 



