IMITATION IN MONKEYS 



549 



easily removed. The median ical devices 

 w hich were to be used as problems for tlie 

 monkeys to solve were adjusted in separate 

 boards. The ca^e was made ready for an 

 experiment by removing; one of the plain 

 boards and substitutinii; in its place a board 

 containing a device. In all, tliere were 

 seven problems, which I designated as 

 follows: chute experiment B, rope 

 experiment, paper experiment, screen 

 experiment, plug experiment, button ex- 

 periment, and string experiment. 



Chute experiment B was a modification 

 of the device used in 

 the chute experiment 

 A, which I have al- 

 ready described. The 

 food-door, instead of 

 being in the top of the 

 cage, was placed in- 

 side the chute. A 

 feeder, which was op- 

 erated by the experi- 

 menter's pulling a 

 string, was adjusted 

 so that it would drop 

 food to the trap-door 

 in the chute. The 

 animal could get this 

 food by leaping to the 

 chute, thrusting a 

 hand up inside, and 

 pulling the string. 



For the rope ex- 

 periment, an opening 

 two inches square was 

 cut near the top of 

 one of the boards at 

 the back of the cage. 

 Into this opening was fitted a door which 

 was hinged to open outward, and which, 

 when closed, was flush with the inside of 

 the board. Before this door a rope was 

 suspended from the top of the cage to 

 the floor. Outside the door was food. 

 The monkey could get food by climb- 

 ing the rope and pushing open the food- 

 door. 



For the paper experiment, an opening 

 about seven inches square was cut in the 

 end board so near the floor that the mon- 

 keys could reach it easily when standing 

 upright. On the outside of this board was 

 adjusted a door, in the center of which 

 was a circular opening two inches in di- 

 ameter. The food-box was fastened to 

 the outside of this door below the opening. 



DIAGRAM OF THE NEW CAGE 

 For a description see page 548-9 



With the door open, a sheet of ordinary 

 letter paper was laid over the opening in 

 the board, and the door was then closed 

 upon it. In this way the opening and the 

 food behind it were obscured by the paper. 

 1 he monkey could get the food by tearing 

 the paper away from the hole. 



This same device, with the paper omit- 

 ted, was used for the screen experiment. 

 The hole in the food-door was obscured 

 by a wooden screen, which was adjusted 

 on the inside of the board. The screen 

 was arranged to slide up and down in a 

 frame. In order to 

 reveal the opening, it 

 must be pushed up at 

 least eight inches. 

 I'he only w^ay the ani- 

 mal could do this 

 when standing on the 

 floor was to place his 

 hands flat against the 

 screen and give an 

 upward push. 



For the plug and 

 button experiments an 

 opening was made in 

 the back of the cage, 

 near the floor, and 

 near the wire end. It 

 was covered by a slide 

 door adjusted on the 

 outside of the board. 

 The door w^as glass, ^ 

 and the monkeys could 

 see the food on the 

 outside of the cage. 

 In the plug experi- 

 ment, a string, at- 

 tached to the slide door, passed down un- 

 derneath the cage and up the corner post 

 opposite the door. The end of the string 

 was fastened to a plug which fitted into a 

 hole from the inside, half-way up this post. 

 The animal could open the door by pull- 

 ing out this plug. He could then get food 

 by going to the door. 



In the button experiment the slide door 

 was opened by a w^ooden button on the 

 inside of the cage and about thirt)^-six 

 inches from the door. From the back of 

 this button a string passed out through an 

 opening and along the back of the cage to 

 the door. The button was near enough to 

 the floor for the monkeys to reach it easily. 

 To open the door, the button, which was 

 fastened to the board by a bolt at the top, 



