178 Animal Intelligence 
The door was held by a bar about 3 by 1 by 5 inches which 
swung on a nail at the left side. 
Box CCC (double bar) was CC with a second similar 
bar on the right side of the door. 
Box NN (hook) was a box about the size of BB with its 
door held by an ordinary hook on the left side which hooked 
through an eyelet screwed into the door. 
Box NNN was NN with the hook on the right instead 
of the left side. 
Box NNNN was box NN with two hooks, one on each 
side. 
Apparatus OO (string box) consisted of a square box tied 
to a string, which formed a loop running over a pulley by 
the cage and a pulley outside, so that pulling on the under 
string would bring the box to the cage. In each experiment 
the box was first pulled back to a distance of 2 feet 3 inches 
from the cage, and a piece of banana putinit. The mon- 
key could, of course, secure the banana by pulling the box 
near enough. 
Apparatus OOO was the same as OO, with the box tied 
to the upper string, so that the upper string had to be pulled 
instead of the lower. 
Box PP was about the size of BB. Its door was held by 
a large string securely fastened at the right, passing across 
the front of the door and ending in a loop which was put 
over a nail on the box at the left of the door. By pulling 
the string off the nail the door could be opened. 
Box RR (wood plug) was a box about the size of BB. 
The door was held by a string at its top, which passed up 
over the front and top to the rear, where it was fastened 
to a wooden plug which was inserted in a hole in the top of 
the box. When the plug was pulled out of the hole, the 
door would fall open. 
