IMITATION IN MONKEYS 



545 



the persons in the room. Gradually, how- 

 ever, his fears wore ojFf, and with Jill he 

 went curiously about the cage, biting at 

 every piece of wood, and poking his fingers 

 into every crack and cranny. A small tree 

 was placed in the cage, and the animals 

 could then stretch their tails by wrapping 

 the tip-end around a branch and suspend- 

 ing their whole weight from the limbs, a 

 performance apparently as enjoyable to the 

 monkeys as swimming is to the average 

 boy. 



The animals did not like to be separated. 

 Jack was especially concerned when Jill 

 came out to get food and he was left alone. 

 Often when alone he w^ould utter a shrill, 

 piercing sound, a veritable bark. This 

 was much unlike their usual noises of 

 whistling and crying, and I took it to be a 

 danger-signal, for Jill never failed to climb 

 the cage, window, or anything else near 

 her, when the cry w^as given. Even when, 

 after a day's fast, she was greedily eating 

 her banana, it would be left with startling 

 suddenness, and she would make no delay 

 until she was at the highest point in the 

 room. She never looked about to discover 

 the danger for herself and never ran on 

 the floor. Her action was always an im- 

 petuous scramble to get up. She never 

 remained up long, and often came down 

 immediately. I never heard her utter the 

 cry. Jack sometimes gave it when she was 

 out of sight, but again when she was in 

 plain view and when there was no dis- 

 turbance in the room. In the wild state, 

 such a cry is probably the signal that some 

 enemy is near, and when given, all that 

 hear it scud to the tree-tops as the place of 

 greatest safety. 



After a few weeks in the laboratory, 

 Jill acquired a pugnacious attitude toward 

 certain persons, usually strangers. I first 

 noticed it one day when the expressman 

 called to leave a package. He entered 

 without noticing her, and when he turned 

 to leave, she was on a cage which he must 

 pass in going to the door. Her mouth was 

 open, her teeth showing, and her body was 

 drawn into a crouching attitude, as if about 

 to spring, I intervened, for fear she might 

 bite or scratch him ; she was of course in- 

 capable of doing serious harm. A day or 

 two later she behaved in the same way 

 toward the laboratory mechanic who came 

 in to do some vi^ork. As he went toward 

 the door, her fury increased like that of a 



dog after a retreating enemy. I began to 

 suspect there was more of bluff than fight 

 in her behavior, and my doubts as to her 

 courage were fully justified a few days 

 later. Experiments were over for the day, 

 and Jill was having her freedom about the 

 room, to the delight of the several persons 

 present. A stranger entered the room. 

 She was at the opposite end, and on top of 

 a six-foot cage, when he entered. She im- 

 mediately prepared for war, and her scold- 

 ing and threatening began. She advanced 

 toward him with short leaps, which grew 

 shorter as she neared him. Her scolding 

 increased ; her hair became erect ; her lips 

 drew back ; her keen teeth were ready to 

 bite, and although her jumps shortened, 

 her anger increased. Suddenly she leaped 

 from the cage toward him (most men 

 w^ould have dodged or struck, but this man 

 did neither) and landed plump upon his 

 chest. Instantly her harsh cries became 

 more like the purr of a cat, and her hand 

 found its way to his jeweled tie-pin and on 

 up to his mustache. They were to be 

 friends ! 



One of the happiest days in Jill's labor- 

 atory experience was the day I hung a 

 rope in the experiment cage. It was an 

 inch rope suspended from the top. Jill 

 leaped to it from the wire side of the cage, 

 and grasped it with hands, feet, and tail. 

 As she swung, pendulum-like, back and 

 forth, her eyes were bright and the corners 

 of her wide-open mouth were drawn back 

 as if she were trying to laugh. It was 

 evidently the expression of delight, and 

 although she uttered no sound, it 'came 

 nearer to a laugh than I have seen on any 

 other animal except the apes. Ever after, 

 the swing was a favorite bit of sport for 

 her. 



Jack never assumed the bluffing attitude 

 toward persons, and he never learned to 

 climb the rope during his life in Cam- 

 bridge. The animals always seemed hun- 

 gry, though they were fed each day with a 

 good supply of raw peanuts, sunflower 

 seed, apples, and bananas. Cornmeal mush, 

 meat scraps, milk, and hard-boiled eggs 

 were given occasionally. Meal worms 

 were a delicacy olYered for good work. 



As soon as the monkej^s were accus- 

 tomed to their new home, I began some 

 preliminary experiments. The desire to 

 get food was used as a motive to induce 

 them to work, about as constant a motive 



