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 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.