SEXUAL BEHAVIOR OF ALBINO RAT 123 



With respect to young animals it has been suggested that many 

 of the play activities anticipate the larger acts that are to be 

 performed by the adult for the preservation of self or the species. 

 Groos ('95) interprets the mounting seen in some animals in 

 infancy as anticipatory practice in the reproductive function. 

 Careful watch was kept for this in the young male rat, but no 

 mounting of the kind done by copulating males or males during 

 the period of pre-copulatory activity was noticed. Two male 

 rats that were over seventy days of age which had not had sexual 

 congress were observed, however, to mount cage-mates in the 

 definitely sexual manner, and attempt a complete copulatory 

 act. Small ('99) speaks of the playful sexual activities of rats 

 under thirty days of age. Our own study does not substantiate 

 his observations. When receptive females were placed with the 

 young males the latter showed no definite sexual excitement until 

 approximately 70 days of age. Prior to that tune the smelling 

 of the vaginal region of receptive females was sometimes more 

 extensive than with normal females, but that may be accounted 

 for by the tendency of young rats to smell at any new odors that 

 are introduced. The secretions of the vagina at the time of the 

 oestrum give rise to new olfactory stimuli to be examined, hence 

 the periods of smelling when females in heat are introduced into 

 the cage are somewhat longer. 



B. Initial copulatory act. The initial copulatory act of the 

 young male resembles that of the experienced adult so closely 

 that differences are not easily discerned. Using as a background 

 the descriptive account (pages 101-105) of the copulatory act of the 

 adult, one can get a fairly complete picture of the initial copu- 

 latory act of the young male by considering the differences be- 

 tween the two. 



a. Copulatory act of the young male contrasted with that of 

 the adult. Two kinds of differences between the act of coition 

 of the adult and the young have been found occurring with a 

 fair degree of regularity. The first consists of differences that 

 arise from structural limitations size, girth of forelimbs, and 

 general bodily vigor; the second, of differences which result 

 from the shunting of sexual behavior by fear responses or dif- 



