No. 491] 



RESPONSE OF TOADS TO SOUND 



681 



within as many minutes, but these may have been the more sensi- 

 tive toads as I had no means of distinguishing one from another. 



From these observations I conclude that both male and female 

 toads can hear and locate in space the call of the male; that the 

 response is unintelligent and mechanical; that to the sound of the 

 mating call a motor response is given, which serves to bring the 

 sexes to the same place; that motion is the stimulus which starts 

 the clasping reflex; that neither sex is able to recognize the other 

 without actual contact; that toads do not quickly profit by experi- 



In comparing the single set of observations here recorded with 

 the experiments of Dr. Yerkes, it will be noted that toads were 

 employed in the former and frogs in the latter; it is not probable, 

 however, that there is any considerable difference in the acoustic 

 sense of such closely related animals. It will also be noted that the 

 observations were made in the early summer, when, according to 

 Dr. Yerkes, the sensitiveness to sound is at its best. But even so, 

 the response observed was greater than the results obtained by Dr. 

 Yerkes seem to indicate. It is possible that the frog is capable of 

 hearing and responding to the call of its mate but has no response 

 ready for the report of a pistol or the Gal ton whistle. It would be 

 interesting to make a j)honographic record of the male call, try its 

 effect on females, and observe the result of changing its pitch, 

 quality, and character. The call of the male is not a contiiuu)us 

 but a throbbing sound. Nerves that are just begituiing to be 

 sensitive to sound might well need a slower rate of vibration than 

 that of the sound itself, and this the throbbing would supj)ly. It 

 was easily perceptible to the ear, so I supjxtsi' could not have been 

 at the rate of more than fifteen or twenty \ihralion> t.. ii second. 

 In Dr. ^Vrkes' experiments the throl)l)ing cKrtric: bell produced 

 "the most marke<l modification (>f reaction,^ probably because it 



lated by soiin.ls a^ lou a^ .".D Nibration. ,HM•^c<•on<l ; "no experi- 

 mental tests were made with lower soimkIs." 



It is posMl.le that the faihue in the ialH,ratnr^ t.. ulnain motor 

 reactions to .soiuul ua^ due t.. the eharaeier of the .sound or to 

 other features of experimentation; on the other hand my observa- 



