MYCETES SENICULUS 197 



exclusive of the tail, is from eighteen to twenty inches, while the tail is about 

 thirty inches in length. When these howlers are seen in the forests, three or 

 four of them are usually together on the topmost branches of the trees. They 

 live largely on fruit, although, like other South American monkeys, they 

 are said to feed also on caterpillars and msects. 



General Behavioral Tendencies — Thorndyke's Observations 



In connection with the general behavioral tendencies of Mycetes 

 seniculus, observations made by Professor Edwin L. Thorndyke, of Columbia 

 University, upon several South American monkeys of the Cebus type (species 

 not stated) are of particular importance. They represent the pioneer effort 

 in the attempt to investigate by accurate psychological method certain 

 aspects of simian behavior. Professor Thorndyke was chiefly interested in the 

 manner in which monkeys may vary from other mammals in the general 

 mental functions revealed by their methods of learning, as well as how they 

 may vary from adult ci\'ilizcd human beings. He recognized three diflerent 

 modes by means of which knowledge may be acquired, namely, learning by 

 trial and accidental success, learning by imitation, and learning by ideation. 

 In the latter case the situation calls up some idea which then arouses the act 

 or may in some way modify it. This, in fact, is the method of learning 

 obviously employed in all advances of civilization. 



Professor Thorndyke devised certain more or less complicated experiments 

 by means of which he tested the monkeys. These tests consisted chiefly 

 of boxes with pegs, bolts, single bars, double bars, hooks, strings and 

 wooden plugs. He arranged the plugs or loops in various combinations, the 

 mastery of which was essential to release the animal from confinement or 

 to admit it to a goal containing food. The tests made with such apparatus 

 yielded negative results and made it clear that monkeys do not learn by 

 reasoning. They do, however, form more associations and associations of 



