THE GENITAL ORGANIS OF THE FEMALE. 



987 



Fig. 531. 



accompanying it proliferates and forms two layers — membrana granulosa — around 

 them. The surrounding connective tissue, pressed out, accommodates itself to 

 the surface of the mass, and gradually constitutes a spherical shell — the fibrous 

 envelope ; then the Graafian vesicle is formed. Soon the two layers of the 

 membrana granulosa separate at one part to form a cavity — the cavity of the 

 vesicle (Fig. 529, 5, G, 7) ; but as the separation is not complete, the ovum, 

 encircled by the internal membrane, lies beside the external membrane. As the 

 cavity of the vesicle enlarges, the tissue of the ovary becomes more condensed, 

 uiid constitutes the fibrous wall, which soon receives a network of vessels. 



(This description does not altogether agree with what is taught by physiologists. 

 It would appear that, in the course of development, groups of cylindrical cells 

 grow up from the stroma of the ovary so as to enclose the primordial ova. 

 These may even form tubular-like structures, called by some German writers the 

 ova-tubes. By-and-by, each ovum is surrounded by cells, forming a little round 

 body called the primary follicle, which consists of the 

 ovum and of epithelial cells surrounding it. The forma- 

 tion of this follicle around each ovum is for the purpose, 

 in due time, of ejecting the ovum from the ovary. The 

 size of the follicle increases by the multiplication of 

 epithelium-cells, and soon a space exists round the ovum 

 which is filled with a fluid — the liquor foUindi. This 

 liquid may be formed by transudation from the surround- 

 ing blood-vessels, and, as some have suggested, by the dis- 

 integration and melting away of some of the epithelial 

 cells. We have now a vesicle filled with fluid — the 

 Graafian vesicle — having a diameter of from "5 to h mm. 

 The connective tissue forms the wall of the vesicle. It 

 consists of : 1. A connective tissue covering the fhera folH- 

 culi, which is formed of two strata — an outer of fibrous 

 tissue, tunica fibrosa ; and an inner, tunica propria, rich 

 in cells and vessels. 2. A lining of stratified follicular 

 epithelium, sometimes called the membrana granulosa. 

 This lining of epithelium-cells forms a prominence at one 

 side, called the cuymilus ovigerus, or discus jiroliqerus, and 

 the layer surrounding the ovum has been termed the 

 tunica granulosa. The space is occupied, as already men- 

 tioned, by the liquor folliculi. When the ovum reaches 

 maturity, the Graafian vesicle is full of fluid, and binges out from the surface of 

 the ovary. It may be mentioned that the primordial ovum is a large round cell, 

 provided with a nucleus and nucleolus ; it originates from a single cell of the 

 germ-epithelium. 



In the Cow, at puberty the stroma of the ovary is crowded with follicles so 

 minute, that it has been computed that a cubic inch would contain two hundred 

 millions of them. 



Puberty occurs earlier in small than in large animals. In the Rabbit, 

 Guinea-pig, Rat, and Birds, it is reached during the first year ; in the Dog and 

 Cat, in the second year ; in the Ox,- Horse, and Lion, in the third year ; in the 

 Camel, in the fifth year ; and in the Elephant, between the twentieth and thirtieth 

 year. Menstruation — or a series of phenomena resembling this function in 

 Woman — occurs in many animals, and is known as the rut, or heat. Cows and 



OVARIUM OF THE RAHIilT 

 AT THE PERIOD OP 

 CESTROM, SHOWING 

 VARIOUS STAGES OF 

 THE EXTRUSION OF 

 OVA. 



