SEXUAL BEHAVIOR OF ALBINO RAT 125 



brown rat chased the young males about the cage and would not 

 permit copulation, but when placed with large males she became 

 quite submissive. 



The sexual aggression of the young male is thwarted by slight 

 resistance of the female more readily than is that of the adult 

 male. Females which back-kick, and run wildly about the cages 

 are less often subjugated by the young male. Likewise those 

 that are extremely lethargic are less often forced into positions 

 favorable for copulation. Although this is due, in part, to a 

 difference in strength of the mature and immature male, it is 

 due in greater part to a difference in aggressiveness. A change 

 in this respect comes on rapidly after the act of coition has been 

 initiated. Craig ('14) reports a similar change in the behavior 

 of one of the doves. 



Another kind of difference centers about the appearance of 

 the elements of the copulatory act in a stage of slight disorgani- 

 zation. Illustrations of this are common in the copulatory 

 attempts of the inexperienced male just prior to the first suc- 

 cessful copulatory act. These elements may consist of mount- 

 ing with or without definite clasp, mounting and palpation of the 

 female's sides, and rarely, mounting and palpation of her sides 

 with feeble pelvic movements that do not effect vaginal en- 

 trance. In the latter case further attempts to repeat the act 

 are not made at once, contrary to the general rule in the case 

 of the experienced male. The frequency of occurence of these 

 partial attempts has been calculated for thirty young males 

 from the records of their behavior with a female just prior to 

 sexual experience. Sometimes the elements which appeared in 

 dissociated or only partially integrated patterns anticipated the 

 complete act by only a few minutes or an hour or two. In other 

 cases they appeared several days earlier. These records show 

 that of the thirty rats: 



Six mounted with firm clasp, but with no other elements of the copu- 

 latory act involved, prior to the first complete act of coition. 



Fourteen mounted and palpated the female's sides, but did not make 

 pelvic movements. 



Eight animals performed the complete act without previously per- 

 forming any of the partial acts given above. 



