IGURE 13.--Multiple-choice apparatus, showing observer's bench
and writing stand.
FIGURE 14.--Apparatus as seen from observer's bench.
FIGURE 15.--Entrances to multiple-choice boxes as seen from
the response-compartment.
FIGURE 16.--Apparatus as seen from the rear, showing exit
doors, food receptacles, and covers for same.

The apparatus was built in room A (figure 12), this room having been
especially planned for it with respect to lighting as well as dimensions
and approaches. It was unfortunately impossible to obtain photographs
showing the whole of the apparatus, but it is hoped that the four
partial views of plate IV may aid the reader who is unfamiliar with
previously described similar devices to grasp readily the chief points
of construction. In this plate, figure 13 shows the front of the
complete apparatus, with the alleyway and door by way of which the
experimenter could enter. The investigator's observation-bench and
record-table also appear in this figure, together with weighted cords
used to operate the various doors and the vertically placed levers by
means of which each pair of doors could be locked. Figure 14 is the view
presented to the observer as he stood on the bench or observation stand
of figure 13 and looked over the entire apparatus. Three of the entrance
doors are shown at the right of this figure as raised, whereas the
remainder of the nine entrance doors of the apparatus are closed. Figure
15 is a view of the entrance doors from below the wire roof of the
apparatus. Again, two of the doors are shown as raised, and three
additional ones as closed. The rear of the apparatus appears in figure
16, in which some of the exit doors are closed and others open. In the
latter case, the food receptacles appear, and on the lower part of the
raised doors of the corresponding boxes may be seen metal covers for the
food receptacles projecting at right angles to the doors, while on the
lower edge of each door is an iron staple used to receive a sliding bar
which could be operated from the observer's bench as a means of locking
the doors after they had been closed. The space beyond the exit doors
was used as an alleyway for the return of the animals to the starting
point.

It will be necessary at various points in later descriptions to refer to
these several figures. But further description of them will be more
readily appreciated after a careful examination of the ground plan of
the apparatus