Correspondence 167 



especially wrong as regards Hyla arborea L. and likely all tree-frogs. Not only myself, but numbers 

 of my friends have observed dozens of times, that tree-frogs in confinement react with croaking on 

 certain definite sounds, even with the promptness of the release of an irritation. Even a loud human 

 voice may induce the male tree-frog to answer; this succeeds with absolute certainty when I pound with 

 a pestle in a brass mortar. This capacity is not very wonderful. For most of the Hyla kinds live by 

 themselves and often widely disseminated over bushes and trees. I may well assume that their loud 

 voice serves the purpose first of all to allure the female during mating time. This also agrees well 

 with Yerkes' observation, who discovered (Joe. cit., p. 304), at least with experiments conducted in 

 winter, that the reaction on auditory irritations was greater in the female of Rana than in the male." 



Mr. Yerkes' fine work will in many respects lead to discussion and to reflection. 

 It appears to me that we have not yet sufficiently laid down, in a precise manner, 

 fundamental definitions for the phenomena that take place in the central apparatus, 

 for instance, such as occur in course of impressions of special sense, of sensation 

 or of motion, that we are still entirely too much influenced by expressions and 

 categories derived from the physiology of the mammalians. There must be, for 

 instance, an essential difference between the receptions and their effects when an 

 animal possesses only the nuclear apparatus, which receives the nerve of special 

 sense, and when it has tracts leading from the nuclear end to the mid-brain (likely 

 always the case) or when it possesses communications between the primary appa- 

 ratus of receptions and the thalamus. It must, finally, make a tremendous differ- 

 ence whether the receptions reach a cerebral cortex or not, and how the latter is 

 constituted. 



Animals possessing apparatus of association in a well-developed cortex will be 

 able to convert their sensory receptions into sensory perceptions. All these postu- 

 lates are inferred from the greater or lesser complications of the structure as revealed 

 by anatomy. 



Psychology will gradually be able to clear them up, when it is furnished with 

 more treatises of the same exactness as the one which I have here the honor to 

 discuss. 



I am, dear sir. 



Yours truly, 



DR. EDINGEH 



Senckenherg Neurologisches Institut, 

 Frankfurt am Main, Germany. 



Statements tn Reply to Dr. Edinger. 



In fairness to Dr. Edinger and myself certain statements concerning his 

 criticisms should be made at once. 



I do not conclude, as Dr. Edinger states, that the frogs observed by me do 

 not hear; on the contrary I conclude and distinctly state in several places (pp. 287, 

 300, 303) that the use of the word hearing is justified by my experiments. The 

 sentence quoted in the criticism, "but the use of the term audition in connection 

 with these reactions has not been justified," when taken from its context means just 

 the opposite of what I intended. What I proceeded to say after that statement 

 was that the previous experiments had not excluded the possibility of the reactions 

 in question being due to the stimulation of cutaneous or other sense organs than the 



