14 ROBERT M. YERKES 



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 start- 

 ing point was possible ; the observation bench C, with its approach 

 step B; 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 cumber- 

 someness of certain portions. It was equally necessary to pro- 

 vide 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 suffi- 

 cient 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 flanges 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. 



