CORRESPONDENCE. 



To the Editor J journal of Comparative Neurology and Psychology: 



Dear Sir: — I have read with great interest the article of Mr. Yerkes on the 

 sense of hearing in frogs, in No. 4, of last year. 



Mr. Yerkes concludes that the frogs observed by him did not hear, but that 

 the receptions transmitted by the Acusticus influenced their movements; "but the 

 use of the term audition in connection with these reactions has not been justified" 

 (p. 301). The behavior of the frogs in freedom as well as in confinement — noises 

 do not cause them to flee — justifies his conclusion. I am well acquainted with the 

 brain of the frog. No connection at present traceable — certainly not a larger one, 

 which could not have escaped our notice — exists between the cerebrum and the 

 acoustic terminal stations in the domain of the mid-brain. The auditory nerve 

 terminates essentially in the medulla oblongata. Even this circumstance alone 

 gives rise to the presumption, that irritations transmitted by the eighth nerve are 

 not turned to account in the same manner by frogs as by higher vertebrates; we 

 cannot, therefore, conclude that hearing is lacking merely on account of the absence 

 of expected movements of flight. Movements alone reveal to us that which is 

 induced by a sensory reception; but it should not necessarily be denied that there 

 are receptions which do not lead to movements. For instance, an animal may 

 hear, without the noise causing it to move. 



It is no doubt true, that Mr. Yerkes' very clever arrangement of experimenta- 

 tion shows that noises irritate the auditory nerve and that they influence the animal's 

 movements, even though in a different way than expected. But those experiments 

 do not allow us to say "the frog does not hear." All we may say is: "the frog does 

 not respond to auditory impressions like a higher animal." 



There are experiences that argue in favor of the assumption that the apparatus 

 for the reception of sound, which in the frog is so clearly present and especially 

 constructed, must allow the possibility of hearing also in the sense of our anrhro- 

 pocentric psychology. When one frog in a pond, for instance raises his voice, 

 on a warm summer evening, another one answers first and gradually others join 

 in, until finally a general croaking extends all over the pond. 



In answer to an inquiry on my part Prof. Boettcher, probably the best 

 informed authority of the present day on amphibian life, the editor of the volume 

 Amphibia in Brehm's "Thierleben" (Animal Life), writes as follows: 



"We can readily agree with Mr. Yerkes' statement regarding 'The Sense of Hearing in Frogs' 

 but we must repel the idea that the conclusions which the author draws from his experiments, should be 

 generalized. 



"His experiments may be correct as far as Rana clamata Daud (clamitans Merr.) and the allied 

 R. catesbiana Shaw, also R. halecina Kalm are concerned, and even for our European kinds R. escu- 

 lenta L. and R. temporaria L.; but they do not apply to all 'Anura Batrachians.' It is very easy to 

 prove that the sentence, he. cit., p. 303: 'When given alone a sound never causes a motor reaction' is 



