The Dancing Mouse: A Study in Animal Behavior

by Robert Mearns Yerkes

[Illustration: FIGURE 13.—The inner ear of the dancer, showing the spiral form of the cochlea. After Kishi.]

The sound-transmitting apparatus of the dancer, according to Kishi, differs only very slightly from that of the gray mouse, and there is no reason to consider the differences which appear as important (21 p. 478).

Almost as amusing as the way in which Cyon's theory of space perception disappears in the light of critical research is Panse's explanation of the deafness of the dancer. Failing to find any defects in the auditory apparatus of the inner ear which seemed adequate to account for the obvious lack of responsiveness to sounds, this investigator concluded that plugs of wax which he had noticed in the auditory meatus of the dancer excluded sounds or in some way interfered with the functioning of the tympanic membrane. Kishi reports that he found such plugs of wax in the ears of one gray mouse, but in none of the dancers which he examined did he discover them (21 p. 479). Panse's explanation of the defective hearing of the dancer neither needs nor deserves further comment.

As one result of his investigation, Kishi is convinced that the dance movements are not due to peculiarities in the semicircular canals and their sense organs, as Rawitz claimed, for the general form and finer structure of these organs in the dancer is practically the same as in the common mouse. Kishi is just as certain that the whirling is not due to defects in the canal organs, as Rawitz is that it is due to such structural conditions! It is rather surprising that any one should feel confident of the power of the microscope to reveal all those structural conditions which are important as conditions of function. Probably there are histological differences between the ear of the dancer and that of the gray mouse, which, although undetectable by scientific means at present, furnish the structural basis for the marked differences in behavior. As has been set forth already (p. 9), Kishi accounts for the dance movements by assuming the inheritance of an acquired character of behavior. This inherited tendency to dance, he thinks, has been accentuated by the confinement of the mice in narrow cages and their long-continued movement in the wheels which are placed in the cages (21 p. 481).

Rawitz, Cyon, and Alexander and Kreidl felt themselves under the necessity of finding peculiarities of behavior in the dancer which could be referred to the various abnormalities of structure which they had either seen or accepted on faith; Kishi found himself in a very different predicament, for he had on his hands the commonly accepted statement that the animals are deaf, without being able to find any structural basis for this defect. To avoid the difficulty he questions the existence of deafness! If perchance they are deaf, he thinks that it is possibly because of the defect in the stria vasculosa. This suggestion Kishi makes despite the fact that our ignorance of the function of the stria renders it impossible for us to do otherwise than guess at its relation to hearing.

We have now briefly reviewed the results of the various important investigations of the behavior and structure of the dancer.

The observations of Cyon, Zoth, and the writer establish beyond doubt the existence of important individual differences in behavior if not of distinct divisions within the species of mouse, and the general results of the several anatomical investigations make it seem highly probable that the structure of the ear, as well as the externally visible structural features of the animals, vary widely. Unfortunately, the lack of agreement in the descriptions of the ear given by the different students of the subject renders impossible any certain correlation of structural and functional facts. That the whirling and the lack of dizziness and of hearing have their structural bases no one doubts, but whether it is in the brain itself, in the sense organs, or in the labyrinth, our knowledge does not permit us to say. With this statement Rawitz, Cyon, and Alexander and Kreidl would not agree, for they believe that they have discovered structural peculiarities which fully explain the behavior of the dancer. Panse and Kishi, on the other hand, contend that the ear gives no structural signs of such peculiarities as the dancing and deafness suggest; they therefore look to the cerebellum for the seat of the disturbance. With the same possibility in mind the author of "Fancy Varieties of Mice" writes: "These quaint little creatures make amusing pets for any one who is not scientific, or very fond of knowing 'the reason why.' In their case, the reason of the peculiarity which gives them their name is rather a sad one. It is now pretty conclusively established that they are no more Japanese than they are of any other country in particular, but that the originators of the breed were common fancy mice which were suffering from a disease of the brain analogous to the 'gid' in sheep. In the latter, the complaint is caused by a parasite in the brain; in the case of the Waltzing Mouse, it is probably due to an hereditary malformation therein. Be this as it may, the breed is now a firmly established one, and the children of waltzing mice waltz like their parents" (32 p. 45). Although it is quite possible that peculiarities in the central nervous system, rather than in the peripheral nervous system, may be responsible for the forms of behavior exhibited by the dancer, it must be remembered that no such peculiarities have been revealed by the examination of the central nervous system. The old fancier has neither better nor worse grounds for his belief than have Panse and Kishi.

So far as the reliability of the anatomical work which has been discussed is in question, it would seem that Rawitz's results are rendered somewhat unsatisfactory by the carelessness of Cyon in fixing the materials; that Panse's descriptions and comparisons are neither careful nor detailed enough to be convincing; that the work of Alexander and Kreidl, as well as that of Kishi, gives evidence of accuracy and trustworthiness. The fact that the statements of Alexander and Kreidl frequently do not agree with those of Kishi proves that there are serious errors in the work of one or another of these investigators. Cyon's discussion of the anatomy of the dancer is not to be taken too seriously, for by his theory of space perception and of a sixth sense he was unduly biased in favor of the structural peculiarities described by Rawitz. Nevertheless, his discussion is not without interest, for the way in which he succeeded in making every structural fact which Rawitz suggested fit into his theories and help to account for the functional peculiarities which he had himself observed, is extremely clever and indicates a splendid scientific imagination.

To sum up: All the facts of behavior and physiology which have been established lead us to expect certain marked structural differences between the dancer and the common mouse. The bizarre movements, lack of equilibrational ability, and the nervous shaking of the head suggest the presence of peculiar conditions in the semicircular canals or their sense organs; and the lack of sensitiveness to sounds indicates defects in the cochlea. Yet, strange as it may seem to those who are not familiar with the difficulties of the study of the minute structure of these organs, no structural conditions have been discovered which account satisfactorily for the dancer's peculiarities of behavior. That the ear is unusual in form is highly probable, since three of the four investigators who have studied it carefully agree that it differs more or less markedly from that of the common mouse. But, on the other hand, the serious lack of agreement in their several descriptions of the conditions which they observed renders their results utterly inconclusive and extremely unsatisfactory. The status of our knowledge of the structure of the central nervous system is even less satisfactory, if possible, than that of our knowledge of those portions of the peripheral nervous system which would naturally be supposed to have to do with such functional peculiarities as the dancer exhibits. So far as I have been able to learn, no investigator has carefully examined the brain and spinal cord in comparison with those of the common mouse, and only those who have failed to find any structural basis for the facts of behavior in the organs of the ear have attempted to account for the dancer's whirling and deafness by assuming that the cerebellum is unusual in structure. We are, therefore, forced to conclude that our knowledge of the nervous system of the dancing mouse does not at present enable us to explain the behavior of the animal.

It seems highly probable to me, in the light of my observation of the dancer and my study of the entire literature concerning the animal, that no adequate explanation of its activities can be given in terms of the structure of the peripheral or the central nervous system, or of both, but that the structure of the entire organism will have to be taken into account. The dancer's physiological characteristics, in fact, suggest multitudinous structural peculiarities. I have confined my study to its behavior, not because the problems of structure seemed less interesting or less important, but simply because I found it necessary thus to limit the field of research in order to accomplish what I wished within a limited period.