Observation of the behavior of the dancer under natural conditions caused me to suspect that it is either defective in color vision or possesses a sense which is very different from human vision. I therefore devised the following extremely simple method of testing the animal's ability to distinguish one color from another. In opposite corners of a wooden box 26 cm. long, 23 cm. wide, and 11 cm. deep, two tin boxes 5 cm. in diameter and 1.5 cm. deep were placed, as is shown in part I of Figure 18. One of these boxes was covered on the outside with blue paper (_B_ of Figure 18), and the other with orange[1] (_O_ of Figure 18). A small quantity of "force" was placed in the orange box. As the purpose of the test was to discover whether the animals could learn to go directly to the box which contained the food, the experiments were made each morning before the mice had been fed. The experimental procedure consisted in placing the individual to be tested in the end of the large wooden box opposite the color boxes, and then permitting it to run about exploring the box until it found the food in the orange box. While it was busily engaged in eating a piece of "force" which it had taken from the box and was holding in its fore paws, squirrel fashion, the color boxes were quickly and without disturbance shifted in the directions indicated by the arrows of Figure 18, I. Consequently, when the animal was ready for another piece of "force," the food-box was in the corresponding corner of the opposite end of the experiment box (position 2, 18, II). After the mouse had again succeeded in finding it, the orange box was shifted in position as is indicated by the arrows in Figure 18, II. Thus the tests were continued, the boxes being shifted after each success on the part of the animal in such a way that for no two successive tests was the position of the food- box the same; it occupied successively the positions 1, 2, 3, and 4 of the figure, and then returned to 1. Each series consisted of 20 tests. [Footnote 1: These were the Milton Bradley blue and orange papers.] [Illustration: FIGURE 18.--Food-box apparatus for color discrimination experiments. _O_, orange food-box; _B_, blue food-box; 1, 2, 3, 4, different positions of the food-boxes, _O_ and _B_; I, II, III, IV, figures in which the arrows indicate the direction in which the food-boxes were moved.] [Illustration: FIGURE 19.--Food-box apparatus with movable partitions. _O_, orange food-box; _B_, blue food-box; _X_, starting point for mouse; _A_, point at which both food-boxes become visible to the mouse as it approaches them; 1, 2, two different positions of the food-boxes; _T_, _T_, movable partitions. (After Doctor Waugh.)]