THE DEVELOPMENT OF A YOUNG MONKEY 129 



grain. Picked up large handfuls, letting most of it slip to 

 ground. Usually managed to get one sun-flower seed into his 

 mouth, "gummed" it round and round but did not crack hull. 



September g. Uses pouch freely, using back of forefinger as 

 do adults for forcing food into mouth. Mother left him more 

 freely than ever before. Uses the humped up, slow "lope" 

 of adult. Covers ground rapidly. Enormous strides within last 

 two days in motor development. Sure of his leaps and does not 

 over-innervate and lose control. Today for first time left mother 

 and ran up inclined plane almost to top. Could not get over 

 edge. Mother paid no attention to him but ran on up incline 

 and sat on shelf. After three or four efforts youngster clam- 

 bered over and sat on shelf. Mother left him to clamber down 

 for food. Played on shelf for half an hour. Mother lay down, 

 fore-feet out like sleeping cat. Baby played leap-frog over her 

 back,' running the whole length of the shelf. At times would stop, 

 sit on haunches, throwing up one hind-foot and slapping it 

 with fore -foot. These movements were all of the relaxed and 

 infantile type. They seemed to be a part of the play. Indeed, 

 in all of his play movements there seem to be as many of the 

 non-adaptive type as of the adaptive. Those multitudinous 

 functions which are to be of use in the adult seem to gain in 

 accuracy only by being exercised in the act for which they were 

 intended, i.e., are slowly learned as they are called for. 



Within the past week all of the vocal sounds of the adult 

 have been heard with the exception of the ones which are used 

 in the exercise of the sexual function. They are in a high fal- 

 setto key. Many of the adult expressive (emotional) movements 

 are present. On viewing Billy through fence (Sept. 5) he began 

 bouncing on fence with hind legs holding on by fore legs. Ro- 

 tated skin of forehead and scalp up and down as he gazed fixedly 

 at Billy and exchanged similar sounds with him. This type of 

 behavior is like that exhibited by two adult strange monkeys 

 placed in adjoining cages. 



Even during this past week when the young monkey has 

 begun showing independence the rigorous vigilance of the mother 

 is never relaxed. She springs to him upon the occasion of any 

 alarming sound or strange or sudden movement of the experi- 

 menter. She is growing more resentful of any liberties with 

 her food. 



