SEXUAL BEHAVIOR OF ALBINO RAT 151 



palpation of female's sides, and reduction of force of backward 

 lunge. More important differences are: Increase of aggressive- 

 ness with sexual experience; incomplete patterns of the act in- 

 volving omission of the essential elements such as palpation, 

 pelvic movements and backward lunge; failure to lick the penis 

 after copulation ; and mounting in a manner that will not permit 

 the completion of the full copulatory act, i.e., mounting at head. 



4. The age at which the initial copulatory act appears is re- 

 lated to general physical development. The earliest age at 

 which the act was initiated in this study was sixty-four days. 

 It does not appear prior to somatic maturity. On the other 

 hand, somatic maturity is not a reliable indication of copulatory 

 ability. 



5. The number of copulations following the initial experience 

 compares favorably with that of adult males. The usual num- 

 ber during thirty minutes subsequent to the first act is from 

 twenty-five to thirty-five. The greatest number observed in 

 this study was 53 during the first twenty minutes. 



6. The movements of a receptive female appear to supply the 

 adequate stimuli for the initiation of the copulatory act. Move- 

 ments of adult rats that simulated those of a female in heat 

 brought out sexual acts, complete in pattern from the male's 

 standpoint, in the case of two males that had not had sexual 

 experience. The quick movements of a guinea pig served to 

 arouse great sexual excitement in a young male. Excitement 

 was accompanied by mounting attempts, but no complete acts. 



7. Sensory controls reveal the following: 



a. Visual stimuli are not essential to the initiation of the copu- 

 latory act. No visible effects in their absence are seen in the 

 nature of the pattern, the pursuit tendency in mounting, the 

 age of first copulation, or the rate at which copulations may take 

 place. 



b. Olfactory stimuli are not necessary for the arousal of sexual 

 excitement or the initiation of the copulatory act. Their ab- 

 sence neither retards the age at which the act first appears, or 

 modifies the sexual drive as manifested by eagerness to copu- 

 late and ability to copulate for a prolonged period of time. 



