118 ROBERT M. YERKES 



merits involving the whole hand or arm, I am rather likely to 

 perform with my right hand. 



It seems not improbable in the light of my own experience 

 that we shall find some specialization among the lower animals 

 with respect to preference for right and left hand or arm. I 

 should not be at all surprised to discover that it is the rule for 

 animals to possess or to develop readily definite preference for 

 one hand in connection with a given act of skill and to have quite 

 as definite a preference for the other hand in connection with a 

 radically different kind of act. 



2. Instinct and emotion 



Of the rnany presumably instinctive modes of behavior which 

 were observed, only those which have to do with social relations 

 seem especially worth reporting. From among them I shall 

 select for description a few which have already been referred 

 to in connection with the experimental observations. 



Maternal Instinct 



Aspects of the maternal instinct I had opportunity to observe 

 in Gertie, who on February 27 gave birth to a male infant, I 

 present below the substance of a previously published note on 

 her behavior (Yerkes, 1915). 



"On February 27 one of the monkeys of our collection gave 

 birth, in the cages at Montecito, to a male infant. The mother 

 is a Macacus cynomolgtis rhesus [P. irits rhesus) who has been 

 described by Hamilton (1914, p. 298) as 'Monkey 9, Gertie, 

 M. cynomolgus rhesus {P. iriis rhesus). Age, 3 years 2 months. 

 (She is now. May 1, 1915, 4 years and 6 months.) Daughter 

 of monkeys 3 and 10. First pregnancy began September, 1913.' 

 The result of this pregnancy was, I am informed, a still-birth. 



" The second pregnancy, which shall now especially concern 

 us, resulted likewise in a still-birth. Parturition occurred Satur- 

 day night, and the writer first observed the behavior of the 

 mother the following Monday morning. In the meantime the 

 laboratory attendant had obtained the data upon which I base 

 the above statements. 



"At the time of parturition Gertie was in a 6 by 6 by 12 foot 

 out-door cage containing a small shelter box, with an excep- 



