MONKEYS —GENEEAL 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 Eeng- 

 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 : — 



' 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 



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