presented as figure 17 In accordance with the labelling of
this figure, the experimenter enters the apparatus room through doorway
16, passes thence through doorways 17 and 10 to the large cage Z, from
which he has direct access to the animals and can bring them into the
apparatus. The multiple-choice mechanism proper, consisting of nine
similar boxes (nine were used instead of twelve as a matter of
convenience of construction, not because this smaller number is
otherwise preferable) is labelled F. These boxes are numbered 1 to 9,
beginning at the left. This numbering was adhered to in the recording of
results throughout the investigation. The other important portions of
the apparatus are the runway D, from which the subject at the
experimenter's pleasure could be admitted through doorway 12 to the
large response-chamber E; the alleyways G, H, and I, by way of which
return to the starting point was possible; the observation bench C, with
its approach step 13; and the observer's writing table A.

In the construction of this large apparatus, it was necessary to make
provision for the extremely destructive tendencies of monkeys and
anthropoid apes,--hence the apparent cumbersomeness of certain portions.
It was equally necessary to provide for the protection of the observer
and the prevention of escape of the subjects by completely covering the
apparatus and alleyways with a heavy wire netting.

Each of the eighteen doors of the multiple-choice boxes, and in addition
doors 11, 12, and 15 of the runway D, were operated by the observer from
his bench C by means of weighted window cords which were carried by
pulleys appropriately placed above the apparatus. Each weight was so
chosen as to be just sufficient to hold its door in position after the
experimenter had raised it. For the convenience of the experimenter in
the rapid operation of the twenty-one doors, the weights for the doors
of runway D were painted gray, those for the entrance doors, white, and
those for the exit doors, black.

In each entrance door, as is shown in figure 15 of plate IV, a window
was cut so that the experimenter might watch the animal after it had
entered a given box, and especially note when it left the box after
having received its reward. This window was covered with wire netting.
No such windows were necessary in the exit doors, but to them were
attached heavy galvanized iron flanges which served to cover the food
receptacles. One of these fla