As I shall hope to make clear in a subsequent discussion of the dancer's peculiarities of behavior, in a chapter on individual differences, there is no sufficient reason for doubting the general truth of Cyon's description, although there is abundant evidence of his inaccuracy in details. If, for the present, we accept without further evidence the statement that there is more than one variety of dancer, we shall be able to account for many of the apparent inaccuracies of description which are to be found in the literature on the animal.
As a result of the examination of the facts which this chapter presents we have discovered at least six important peculiarities of behavior of the dancer which demand an explanation in terms of structure. These are: (1) the dance movements—whirling, circling, figure-eights, zigzags; (2) restlessness and the quick, jerky movements of the head; (3) lack of responsiveness to sounds; (4) more or less pronounced deficiency in orientational and equilibrational power; (5) lack of visual dizziness; (6) lack of rotational dizziness.
Naturally enough, biologists from the first appearance of the dancing mouse in Europe have been deeply interested in what we usually speak of as the causes of these peculiarities of behavior. As a result, the structure of those portions of the body which are supposed to have to do with the control of movement, with the phenomena of dizziness, and with the ability to respond to sounds, have been studied thoroughly. In the next chapter we shall examine such facts of structure as have been discovered and attempt to correlate them with the facts of behavior.
CHAPTER V
STRUCTURAL PECULIARITIES AND BEHAVIOR
The activities of an animal are expressions of changes which occur in its structure, and they can be explained satisfactorily only when the facts of structure are known. Such peculiarities of activity as are exhibited by the dancing mouse, as contrasted with the common mouse, suggest at once that this creature has a body which differs in important respects from that of the ordinary mouse. In this chapter I shall present what is known concerning the structural bases for the whirling, the lack of equilibrational ability and of dizziness, the quick jerky head movements, the restlessness, and the partial or total deafness of the dancing mouse.
Comparative physiologists have discovered that the ability of animals to regulate the position of the body with respect to external objects and to respond to sounds is dependent in large measure upon the groups of sense organs which collectively are called the ear. Hence, with reason, investigators who sought structural facts with which to explain the forms of behavior characteristic of the dancer turned their attention first of all to the study of the ear. But the ear of the animal is not, as might be supposed on superficial examination, a perfectly satisfactory natural experiment on the functions of this group of sensory structures, for it is extremely uncertain whether any one of the usual functions of the organ is totally lacking. Dizziness may be lacking, and in the adult hearing also, but in general the functional facts lead the investigator to expect modifications of the sense organs rather than their absence.
I shall now give an account of the results of studies concerning the structure of the ear and brain of the dancer. Since the descriptions given by different anatomists contradict one another in many important points, the several investigations which have been made may best be considered chronologically.
Bernhard Rawitz (25 p. 239) was the first investigator to describe the structure of the ear of the Japanese or Chinese dancers, as he calls them. The definite problem which he proposed to himself at the beginning of his study was, what is the structural basis of the whirling movement and of the deafness of the mice?
In his first paper Rawitz described the form of the ears of five dancers. His method of work was to make microscopic preparations of the ears, and from the sections, by the use of the Born method, to reconstruct the ear in wax. These wax models were then drawn for the illustration of the author's papers (Figures 8, 9, 10).