The Dancing Mouse: A Study in Animal Behavior

by Robert Mearns Yerkes

Kishi's work was evidently done with admirable carefulness. His methods in the preparation of his materials, so far as can be judged from his report, were safe and satisfactory, and his descriptions of results are minute and give evidence of accuracy and conscientious thoughtfulness. The material for his histological work he obtained from three different animal dealers. It consisted of fifteen adult and nineteen young dancers, and, as material for comparison, ten common gray mice. The animals were studied first biologically, that their habits and behavior might be described accurately and so far as possible accounted for in the light of whatever histological results might be obtained subsequently; then they were studied physiologically, that the functional importance of various organs which would naturally be supposed to have to do with the peculiarities of the mouse might be understood; and, finally, they were killed and their ears and portions of their brains were studied microscopically, that structural conditions for the biological and physiological facts might be discovered.

The ear, which was studied by the use of several series of sections, as well as in gross dissections, is described by Kishi under three headings:—

(1) The sound-receiving apparatus (auditory organs).

(2) The static apparatus (equilibrational organs).

(3) The sound-transmitting apparatus (ear drum, ear bones, etc.).

The chief results of his structural investigation may be stated briefly under these three headings. In the sound-receiving or auditory apparatus, Kishi failed to find the important deviations from the usual structure of the mammalian ear which had been described by Rawitz. The latter distinctly says that although the organ of Corti is present in all of the whirls of the cochlea, the auditory cells in it are noticeably degenerate. Kishi does not agree with Panse's statement (21 p. 476) that the auditory organ of the dancer differs in no important respects from that of the common mouse, for he found that in certain regions the hair cells of the organ of Corti were fewer and smaller in the dancer. He therefore concludes that the auditory organ is not entirely normal, but at the same time he emphasizes the serious discrepancy between his results and those of Rawitz. In not one of the ears of the twelve dancers which he studied did Kishi find the direct communication between the utriculus and the scala tympani which Rawitz described, and such differences as appeared in the organ of Corti were in the nature of slight deviations rather than marked degenerations.

In the outer wall of the ductus cochlearis of the dancer the stria vasculosa is almost or totally lacking, while in the gray mouse it is prominent. This condition of the stria vasculosa Kishi was the first to notice in the dancer; Alexander and Kreidl had previously described a similar condition in an albino cat. If, as has been supposed by some physiologists, the stria vasculosa is really the source of the endolymph, this state of affairs must have a marked influence on the functions of the auditory apparatus and the static apparatus, for pressure differences between the endolymph and the perilymph spaces must be present. And, as Kishi points out, should such pressure differences be proved to exist, the functional disturbance in the organ of hearing which the lack of responses to sounds seems to indicate might better be ascribed to them than to the streaming of the endolymph from the canals into the cochlea as assumed by Rawitz (21 p. 477). Kishi merely suggests that the condition of the stria may account for the deafness of the mouse; he does not feel at all confident of the truth of his explanation, and he therefore promises in his first paper a continuation of his work in an investigation of the functions of the stria. This, however, he seems not to have accomplished thus far.

[Illustration: FIGURE 12.—The inner ear of the dancer. Reproduced from Kishi's figure in the Zeitschrift für wissenschaftliche Zoölogie, Bd. 71. c.c. crus simplex; o.b. anterior vertical canal; h.b. posterior vertical canal; a.b. horizontal canal.]

The static apparatus Kishi describes as closely similar in form to that of the gray mouse. In none of his twelve preparations of the ear of the dancer did he find such abnormalities of form and connections in the semicircular canals as Rawitz's figures and descriptions represent. Rawitz states that the anterior canal is normal except in its lack of connection with the posterior and that the posterior and horizontal are much reduced in size. Kishi, on the contrary, insists that all of the three canals are normal in shape and that the usual connection between the anterior and the posterior canals, the crus simplex, exists. He justifies these statements by presenting photographs of two dancer ears which he carefully removed from the head. Comparison of these photographs (Figures 12 and 13) with Rawitz's drawings of the conditions of the canals and sacs as he found them (Figures 8, 9, and 10), and of both with the condition in the typical mammalian ear as shown by Figure 7, will at once make clear the meaning of Kishi's statements. That Rawitz's descriptions of the canals are not correct is rendered almost certain by the fact that Panse, Baginsky, Alexander and Kreidl, and Kishi all agree in describing them as normal in form.

The only important respects in which Kishi found the membranous labyrinth, that is, the canals and the ear sacs, of the dancer to differ from that of the gray mouse are the following. In the dancer the cupola of the crista acustica is not so plainly marked and not so highly developed, and the raphae of the ampullae and canals, which frequently are clearly visible in the gray mouse, are lacking (21 p. 478).