CESTROUS CYCLE IN THE GUINEA-PIG. 23! 



observation on the oestrous discharge in the guinea-pig it is 

 probable that this plug-like structure was nothing else than a 

 concentrated accumulation of such a discharge, it having become 

 unusually dense or dried out. In fact, as will be shown beyond, 

 the superficial portion of the vaginal plug is actually the sluffed- 

 off vaginal epithelium surrounding the coagulated seminal fluid. 

 Thus the plug is partly of vaginal origin. 



In later papers Lataste makes many contributions to the 

 knowledge of the vaginal plug. In 1883 he described the vaginal 

 plug in other rodents and pointed out that this formation was 

 evidently not limited to a few species but was characteristic of 

 the entire class. 



Regarding the function of the vaginal plug, he slightly modifies 

 his former position and concludes that its role is not only to 

 prevent the sperm from flowing out of the vagina but rather by 

 a filling up to push the sperm into the uterus. He extended the 

 observation of Blanchard that the vaginal plug consists of two 

 parts, differing in structure, a central core and a superficial en- 

 velope. He described the central part as consisting chiefly of the 

 coagulated secretion of the seminal vesicles and also of a quantity 

 of mucus, i888a, while the superficial portion, envelop pe vaginale, 

 was formed of stratified epithelial cells. The enveloppe vaginale 

 is produced in the female by a rapid exfoliation of cells from the 

 uterine glands and the vaginal walls on account of the irritating 

 presence of the coagulated core. (His conception of the cause 

 of the exfoliation is entirely incorrect.) The envelopment of the 

 core by loosened epithelium from the vaginal wall serves to 

 make easy the expulsion of the vaginal plug. This epithelial 

 production he thinks is probably of a pathological nature and 

 ' may be compared to the condition in women known as vagimte 

 exfolianle. 



These studies of more than thirty years ago by Lataste are in 

 most respects surprisingly correct and it is only the nature of 

 the process by which the outer epithelial envelope is formed with 

 which we would materially differ. 



Tafani, in 1888, described the vaginal plug in the mouse and 

 found it to fall out about thirty hours after copulation. 



Steinach ('94) found that the removal of the seminal vesicles 



