The Mental Life of the Monkeys 179 
Box SS (triple; wood-plug, hook and bar) was a box 
about the size of BB. To open the door, a bar had to be 
pushed around, a hook unhooked and a plug removed from 
a hole in the top of the box. 
Box TT (nail plug) was 14 by 10 by 10 inches with a door 
5-5 by ro on the right side of the front, the rest of the front 
being barred up. The door was hinged at the bottom and 
fastened at its top to a wire which was fastened to a nail 
2.5 inches long, which, when inserted in a hole 0.25 inches 
in diameter at the back of the top of the box, held the door 
closed. By drawing out this nail and pulling the door 
the animal could open the door. 
Box VV (plug at side) was a box about 18 by 10 by 10, 
the door held by a plug passing through a hole in the side 
of the box. When the plug was pulled out, the door could 
be pushed inward. 
Box W (loop) was 17 by 10 by ro inches with a door 5 by 9 
at the left side of its front hinged at the bottom. The door 
was prevented from falling inward by a wire stretched 
behind it. It was prevented from falling outward by a 
wire firmly fastened at the right side and held by a loop over 
a nail at the left. By pulling the loop outward and to the 
left it could be freed from the nail. The door could then 
be pulled open. 
Box WW (bar inside) was 16 by 14 by 10 inches with a 
door 4 by 11 at the left of its front hinged at the bottom. 
The door could be pushed in or pulled out when a bar on 
its inside was lifted out of a latch. The bar was accessible 
from the outside through an opening in the front of the 
box. It had to be lifted to a height of 1.5 inches (an angle 
of about 30°). 
Box XX (bar outside) was about 13 by 11 by ro inches 
with a door 7 by 8 on the left side of the front. The door 
