THE DEVELOPMENT OF A YOUNG MONKEY 135 



The first teeth, the incisors, were cut during the fifth week; 

 the molars did not appear until the 15th. Teething seemed to 

 be somewhat difficult. The first manifestations of sexual activ- 

 ity were noted during the ninth week. 



Sensory-Motor 



First week. On the first day the little monkey was very still, 

 moving only when forced to do so by the movements of the 

 adult. However, certain reflexes seemed to be well established 

 even on this day. Those observed were sucking, grasping, 

 muzzling, crying, sneezing, winking (not in response to visual 

 stimuli), inco-ordinated movements of the legs when the stim- 

 ulus for grasping was removed, and an increased muscular 

 tension of the legs in response to the mother's movements. 



During the second day there appeared to be a slight un- 

 adaptive response to sound. In the human infant this varies 

 in time of appearance from the second to the tenth day. By 

 the third day his strength had increased so that his grasp upon 

 his mother's hair had become secure. The head and eyes were 

 at this age first turned to follow a moving object. Two days 

 later appeared the reflex grasping at an object seen. 



Second week. By the end of the first week his muscular activ- 

 ity was greatly increased, although most of his movements were 

 still of the non-adaptive type. Complex co-ordinated movements 

 of the limbs, as in jumping, appeared, and voluntary reaching 

 toward moving objects became more frequent. The scratching 

 reflex was established. On the nth day he reached out and 

 grasped small objects. By this time his responses to sound 

 indicated some degree of localization. On the 12th day he 

 first attempted to walk. The movements were very badly 

 executed and showed a decided lack of co-ordination. 



Third week. The third week, the first week of walking, was 

 marked by a tremendous increase in his muscular control. The 

 movements of the larger muscles of the limbs became fairly well 

 adjusted to the demands made upon them, and many infantile 

 movements were gradually made adaptive. The first definite 

 play activities appeared, with contractions of the facial muscles 

 in pursing the lips. 



