MENTAL LIFE OF MONKEYS AND APES 13 



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 ap- 

 paratus. 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 w^hich 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 



