124 CALVIN P. STONE 



ferences that appear to arise from slightly incomplete coordina- 

 tion of the elements of the complex mechanism involved in the 

 copulatory act. Differences of the first type, being relatively 

 unimportant for this study, will be passed over with only brief 

 remarks as to their nature. 



Limitations in the size of the male and the girth of his fore- 

 limbs cause a slight difference in the placement of the fore- 

 paws on the body of the female as he stands in the copulatory 

 position. Difference in strength of the fore-limbs results in 

 palpation less vigorous than that of the adult. The palpation 

 suffices, nevertheless, to elicit the necessary cooperation of the 

 female. Frequently the backward lunge of the young is greatly 

 reduced in force or even eliminated entirely the male slipping 

 smoothly from the mounting position. 



The second group of differences between the experienced male 

 and the novice needs more careful consideration for it embraces 

 factors that are concerned with the initiation of the copulatory 

 response. During the tests for copulation in young males fear 

 responses, aroused by an attack or threatening attitude of the 

 female, caused the male to move as far from her as the space in 

 the cage permitted. There he remained quietly but on guard 

 against further assault. These responses sometimes last only a 

 few minutes, but in other cases more than an hour. Young rats 

 which had recently been pummeled or bitten severely by adult 

 rats during the daily observation periods sometimes exhibited 

 fear responses to the quick movements of the receptive female 

 in the cage. Such fear responses were sometimes aroused by 

 very docile females which were responding to the male's nosing 

 and licking with the spasmodic jumping that characterizes the 

 female in heat. Evidently the young male does not readily 

 differentiate these quick responses from the aggressive move- 

 ments of attack, and therefore, responds in a manner appro- 

 priate to the avoidance of punishment rather than in a manner 

 appropriate to effecting copulation. Fear responses of this 

 type are seldom seen in the adult male, and they quickly disappear 

 in the young after copulatory experience. In this connection 

 it will be recalled that, according to Miller ('11), the female 



