MONKEYS —GENERAL INTELLIGENCE. 
481 
The orang which Cuvier had used to draw a chair from 
one end to the other of a room, in order to stand upon 
it so as to reach a latch which it desired to open ; and in 
this we have a display of rationally adaptive action 
which no dog has equalled, although, as in the case before 
given of the dog dragging the mat, it has been closely 
approached. Again, Eengger describes a monkey em- 
ploying a stick wherewith to prise up the lid of a chest, 
which was too heavy for the animal to raise otherwise. 
This use of a lever as a mechanical instrument is an 
action to which no animal other than a monkey has ever 
been known to attain ; and, as we shall subsequently see, 
my own observation has fully corroborated that of Reng- 
ger in this respect. More remarkable still, as we shall 
also subsequently see, the monkey to which I allude as 
having myself observed, succeeded also by methodical 
investigation, and without any assistance, in discovering 
for himself the mechanical principle of the screw ; and 
that monkeys well understand how to use stones as ham- 
mers is a matter of common observation since Dampier 
and Wafer first described this action as practised by 
these animals in the breaking open of oyster-shells. The 
additional observation of Gernelli Carreri of monkeys 
thrusting stones into the open valves of oysters so as 
to save themselves the trouble of smashing the shells, 
though not incredible, requires confirmation. But Mr. 
Haden, of Dundee, has communicated to me the follow- 
ing very remarkable appreciation of mechanical principles 
which he himself observed in a monkey (species not noted), 
and which would certainly be beyond the mental powers 
of any other animal : — - 
4 A large monkey, confined alone in a large cage, had 
its sleeping-place in the form of a kind of hut in the 
centre of the cage. Springing near the hut was a tree, 
or imitation tree, the main branch of which ascended 
over the top of the hut, and then came forwards 
away from it. Whether the roof of the hut enabled 
this animal to gain any part of this branch, I did not 
observe, but only remarked its method at the time of 
gaining the part of the branch which led frontwards, and 
