The peculiarities of behavior of the dancing mouse are responsible alike for the widespread interest which it has aroused, and for its name. In a little book on fancy varieties of mice, in which there is much valuable information concerning the care of the animals, one who styles himself "An old fancier" writes thus of the behavior of the dancer: "I believe most people have an idea that the waltzing is a stately dance executed on the hind feet; this is not so. The performer simply goes round and round on all fours, as fast as possible, the head pointing inwards. The giddy whirl, after continuing for about a dozen turns, is then reversed in direction, and each performance usually occupies from one to two minutes. Whether it is voluntary or not, is difficult to determine, but I am inclined to think the mouse can refrain if it wishes to do so, because I never see them drop any food they may be eating, and begin to waltz in the midst of their meal. The dance, if such it can be called, generally seizes the mouse when it first emerges from its darkened sleeping place, and this would lead one to suppose that the light conveys an impression of shock to the brain, through the eyes, which disturbs the diseased centers and starts the giddy gyrations. The mice can walk or run in a fairly straight line when they wish to do so." Some of the old fancier's statements are true, others are mere guesses. Those who have studied the mice carefully will doubtless agree that he has not adequately described the various forms of behavior of which they are capable. I have quoted his description as an illustration of the weakness which is characteristic of most popular accounts of animal behavior. It proves that it is not sufficient to watch and then describe. The fact is that he who adequately describes the behavior of any animal watches again and again under natural and experimental conditions, and by prolonged and patient observation makes himself so familiar with his subject that it comes to possess an individuality as distinctive as that of his human companions. To the casual observer the individuals of a strange race are almost indistinguishable. Similarly, the behavior of all the animals of a particular species seems the same to all except the observer who has devoted himself whole-heartedly to the study of the subject and who has thus become as familiar with their life of action as most of us are with that of our fellow-men; for him each individual has its own unmistakable characteristics. I shall now describe the behavior of the dancing mouse in the light of the results of the observation of scores of individuals for months at a time, and of a large number of experiments. From time to time I shall refer to points in the accounts of the subject previously given by Rawitz (25 p. 236), Cyon (9 p. 214), Alexander and Kreidl (1 p. 542), Zoth (31 p. 147), and Kishi (21 p. 479).