Individuals three weeks old showed less hesitation about trying to creep along such a narrow pathway than did full-grown dancers three or four months old; and these, in turn, were not so timid apparently as an individual one year old. But the younger animals fell off more frequently than did the older ones. [Illustration: FIGURE 4.--Zoth's photographs of dancers crossing bridges and climbing rods. Reproduced from _Pfluger's Archiv_, Bd. 86.] [Illustration: FIGURE 5--Tracks of common mouse Reproduced from Alexander and Kreidl's figure in _Pfluger's Archiv_, Bd 82] [Illustration: FIGURE 6--Tracks of dancing mouse Reproduced from Alexander and Kreidl's figure in _Pfluger's Archiv_ Bd 82] Additional support for these statements concerning equilibrational ability is furnished by the observations of Kishi (21 p. 482). He built a wooden bridge 60 cm. long, 1 cm. wide at one end, and 1/2 cm. at the other, and supported it at a height of 30 cm. above the ground by posts at the ends. On this bridge ten dancers were tested. Some attempted to move sidewise, others began to whirl and fell to the ground; only one of the ten succeeded in getting all the way across the bridge on the first trial. The second time he was tested this individual crossed the bridge and found the post; and the third time he crossed the bridge and climbed down the post directly. The others did not succeed in descending the post even after having crossed the bridge safely, but, instead, finally fell to the floor from awkwardness or exhaustion. On the basis of these and other similar observations, Kishi says that the dancer possesses a fair degree of ability to orient and balance itself. Inasmuch as equilibration occurs similarly in darkness and in daylight, Zoth thinks that there is neither visual dizziness nor fear of heights. But it is doubtful whether he is right concerning fear. There is no doubt in my mind, in view of the way the mice behave when placed on an elevated surface, that they are timid; but this is due probably to the uncomfortable and unusual position rather than to perception of their distance from the ground. That they lack visual dizziness seems fairly well established. When rotated in a cyclostat[1] the dancer, unlike the common mouse, does not exhibit symptoms of dizziness. The following vivid description of the behavior of both kinds of mice when rotated is given by Alexander and Kreidl (1 p. 548). I have not verified their observations. [Footnote 1: An apparatus consisting of a glass cylinder with a mechanism for turning it steadily and at different speeds about its vertical axis.]