NOTES ON THE DEVELOPMENT OF A YOUNG MONKEY 



K. S. LASHLEY AND JOHN B. WATSON 

 From the Psychological Laboratory of The Johns Hopkins University 



Seven Plates 



Since some interest attaches to the development of the young 

 of any species of animaj on account of its bearing upon the con- 

 trol of experimentation in behavior work, it seems worth while 

 to present the diary given below of the growth of a young 

 Macacus rhesus monkey. The diary affords some rather inter- 

 esting points of comparison between the development of the 

 human infant and the young monkey. While comparisons can 

 not be closely drawn it may be said at the outset that the differ- 

 ence in the motor and sensory preparation of the two species 

 of young at birth is enormous and that the more rapid course 

 of development in the young monkey is still more remarkable. 

 We were not at all prepared to find the absence of a prolonged 

 period of infancy in the monkey. That this is the case is appar- 

 ent from our notes. 



The two male monkeys in the Johns Hopkins Laboratory were 

 purchased at Chicago in 1 904-1 905. The older monkey, Jimmie, 

 was probably at the time of purchase three years old, and the 

 second, Billy, about one year of age. The female, Dolly, was 

 purchased in Baltimore in 1907. She was probably three 

 years old at purchase. Their ages now are (J) eleven, (B) eight, 

 and (D) eight respectively. Until 1911 the monkeys lived 

 together at various times in the ordinary large laboratory cages. 

 A change was then made so as to give the animals greater 

 freedom. A yard was fenced in which connected by a chute 

 (i2 /r xi2 // ) with a steam heated room. The animals could 

 spend their time at will either in the yard or in the room. 

 Even in the coldest weather a large part of their time was spent 

 in the open yard. 



During the three or four years prior to this change in their 

 living arrangements copulation between J. and D. took place 

 frequently but there was never any evidence of conception 

 resulting. We were accordingly not expecting the birth of the 



114 



