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). The principal results of the early work of Rawitz are summed up in the following quotation from his paper: "The Japanese dancing mice have only one normal canal and that is the anterior vertical. The horizontal and posterior vertical canals are crippled, and frequently they are grown together. The utriculus is a warped, irregular bag, whose sections have become unrecognizable. The utriculus and sacculus are in wide-open communication with each other and have almost become one. The utriculus opens broadly into the scala tympani, and the nervous elements of the cochlea are degenerate.