CESTROUS CYCLE IN THE GUINEA-PIG. 22Q 



hasten ovulation, or that the act itself may facilitate the bursting 

 of the Graafian follicles, which is a very old conception. 



The act of copulation is short, lasting a few seconds only, while 

 the preceding time of sexual excitement leading up to it is rather 

 long. The male becomes excited by the presence of the female 

 some time before she reaches the proper condition for copulation. 

 A male after long isolation from females becomes sexually excited 

 by the presence of any female irrespective or her sexual condition, 

 and he invariably attempts to copulate. Nevertheless, the 

 excitement of the male is not so strong nor prolonged when in 

 the company of a female during sexual inactivity as with one 

 during her sexual season. When the female is nearing oestrus 

 the male is extremely excited and tries again and again to 

 copulate, while at other times he soon tires and loses interest 

 and ceases his aggressive behavior. 



The male and female never fight during the long period of 

 aggressiveness on the part of the male, which often lasts for 

 many hours. The male tries to induce the female to copulate by 

 irritation and excitement rather than by forcing her. The female 

 may at times become nervous and attempt to bite the male, 

 but an actual fight such as occasionally occurs between two 

 males never takes place. No mating by force is observed; the 

 consent of the female is necessary for the completion of copula- 

 tion. Copulation is followed by a state of relaxation similar to 

 that observed among mammals in general, and immediately 

 afterwards both male and female may spend some time in cleaning 

 their external genitalia. 



3. THE VAGINAL PLUG, ITS FORMATION, LENGTH OF EXISTENCE 

 AND MANNER OF DISCHARGE. 



The spermatic fluid of the guinea-pig, especially that portion 

 derived from the seminal vesicles, on entering the vagina of the 

 female coagulates to form the boudwn vaginal, a rigid plug, 

 filling the lumen of the vagina. This plug prevents the outflow 

 of the sperm after every copulation. Such a vaginal plug has 

 been described in many species of rodents and seems in general 

 to be characteristic of this class of mammals. It was first 

 observed in the guinea-pig by Leuckart in 1847. He correctly 



