TRIAL AND ERROR REACTIONS IN MAMMALS 



35 



gain by experience the information that the above inscriptions 

 would have afforded. 



The floor of the apparatus is of wood, and the top of wire 

 netting, and both are of the form shown in Fig. i . The narrow, 

 rectangular part of this figure represents the entrance hall (EH, 

 Fig. i). This hall can be entered by way of an entrance door 

 (Ent. D, Fig. i), which will swing in the inward direction only, 

 and which fits so snugly within its frame that, once it is closed, 

 it cannot be opened from within the apparatus. It is hung a 

 little out of plumb, so that it will always swing to the closed 

 position when not actually held open by the subject. 



Figure 2 — An exit door, set within its frame, and equipped with button and button 

 strings. B, Button; S^ String number 1; S^, String number 2. 



At the opposite, broader end of the apparatus are four exit 

 doors (Ex D-i, Ex D-2, Ex D-3, Ex D-4, Fig. i). Each of these 

 exit doors opens outward only, and when released from pressure 

 swings to the closed position. Like the entrance door, the exit 

 doors are hung out of plumb. 



The exit doors just described are equidistant from point O 

 in Fig. I. 



Figure 2 is intended to show the manner in which the various 

 exit doors can be " locked " or " unlocked " without the sub- 



