nges is labelled o in figure 17. The food
receptacles were provided by boring holes in a 2 by 4 inch timber
securely nailed to the floor immediately outside of the exit doors. Into
these holes aluminum cups fitted snugly, and the iron flanges, when the
doors were closed, fitted so closely over the cups that it was
impossible for the animals to obtain food from them.

[Illustration: FIGURE 17.--Ground plan of multiple-choice apparatus in
experiment room A. Scale 1/60

A, record stand; C, bench for observer; B, step as approach to C; D,
alleyway leading to E, response-compartment; F, one of the nine (1-9)
similar multiple-choice boxes; G, H, alleyways leading from boxes to
starting point at D; I, alleyway used by experimenter as approach to
rear of apparatus; W, W, windows; P, alleyway; Z, large cage; 16,
entrance to room A; 17, entrance to apparatus and thence via 10 to
cages; 18, entrance to alleyway 1; 11, 15, entrances to D; 12, entrance
to E; 13, entrance door of box 5; 14, exit door of box 5; o, cover for
food receptacle.]

As originally constructed, no provision was made in the apparatus for
locking the entrance and exit doors of the several boxes when they were
closed. But as two of the subjects after a time learned to open the
doors from either outside or inside the boxes, it became necessary to
introduce locking devices which could be operated by the experimenter
from the observation bench. This was readily accomplished by cutting
holes in the floor, which permitted an iron staple, screwed to the lower
edge of each door, to project through the floor. Through these staples
by means of a lever for each of the nine boxes, the observer was able to
slide a wooden bar, placed beneath the floor of the room, thus locking
or unlocking either the entrance door, the exit door, or both, in the
case of any one of the nine boxes.

Since figure 17 is drawn to scale, it will be needless to give more than
a few of the dimensions of the apparatus. Each of the boxes was 42
inches long, 18 inches wide, and 72 inches deep, inside measurements.
The alleys D, I, and H were 24 inches, and G 30 inches wide, by 6 feet
deep. The doors of the several boxes were 18 inches wide, by 5 feet
high, while those in the alleyways were 24 inches wide by 6 feet high.
The response-compartment E of figure 17 was 14 feet 4 inches, by 8 feet,
by 6 feet in depth. In order that the apparatus might be used with adult
human subjects conveniently, if