Finally, in concluding this chapter, I may add that in those aspects of behavior which received attention in the early chapters of this volume the dancers differ very markedly. Some climb readily on vertical or inclined surfaces to which they can cling; others seldom venture from their horizontally placed dance floor. Some balance themselves skillfully on narrow bridges; others fall off almost immediately. My own observations, as well as a comparison of the accounts of the behavior of the dancer which have been given by Cyon, Zoth, and other investigators, lead me to conclude that there are different kinds of dancing mice. This may be the result of crosses with other species of mice, or it may be merely an expression of the variability of an exceptionally unstable race. I can see no satisfactory grounds for considering the dancer either abnormal or pathological. It is a well-established race, with certain peculiarities to which it breeds true; and no pathological structural conditions, so far as I have been able to learn, have been discovered. I have presented in this chapter on differences a program rather than a completed study. To carry out fully the lines of work which have been suggested by my observations and by the presentation of results would occupy a skilled observer many months. I have not as yet succeeded in accomplishing this, but my failure is not due to lack of interest or of effort. CHAPTER XVIII THE INHERITANCE OF FORMS OF BEHAVIOR In a general way those peculiarities of behavior which suggested the name dancing mouse are inherited. Generation after generation of the mice run in circles, whirl, and move the head restlessly and jerkily from side to side. But these forms of behavior vary greatly. Some individuals whirl infrequently and sporadically; others whirl frequently and persistently, at certain hours of the day. Some are unable to climb a vertical surface; others do so readily. Some respond to sounds; others give no indications of ability to hear. I propose in this chapter to present certain facts concerning the inheritance of individual peculiarities of behavior, and to state the results of a series of experiments by which I had hoped to test the inheritance of individually acquired forms of behavior. My study of the nature of the whirling tendency of the dancer has revealed the fact that certain individuals whirl to the right almost uniformly, others just as regularly to the left, and still others now in one direction, now in the other. On the basis of this observation, the animals have been classified as right, left, or mixed whirlers. Does the dancer transmit to its offspring the tendency to whirl in a definite manner?