The science of life : fully illustrated in tone and line and including many diagrams

BOOK 1

of passages and compartments: the uterus, or womb, where the growing embryo is housed and nourished, the two upper oviducts, leading ova from the ovaries to the womb, and the passage which receives the male gametes. As in the male, these compartments are provided with various accessory glands. The ovary is not tubular in structure as a testis is; the main part of its substance consists of a network of connective tissue bearing in its meshes the interstitial cells, to whose function we shall return. Dotted about in this mass are the ova in various

Ureter

Rectum

Uterus | ry Thine A

Oviduct

Uterus

Oviduct

Fig. 61. Above, Front View of the Female Reproductive Organs (the top of the bladder is removed to display the parts

more clearly). cavities.

stages of development. The ova lie in spherical vesicles called, after their seventeenth century discoverer, the Graafian follicles. The follicles of the youngest and smallest ova consist of a simple layer of cubical cells surrounding the ovum, and nursing and nourishing it, but as the ovum grows the follicle becomes more and more complicated. The largest ova, which are approaching maturity, are surrounded by two layers of follicular tissue each several cells thick, and separated from each other by a space containing a nutrient fluid.

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THE SCIENCE OF LIFE

Below, the same in section, to show their

CHAPTER 4

Thus the female gametes are treated with very much more respect than the male. The spermatozoa proliferate almost untended

in the testis, but the developing ova are

elaborately cared for by the cells of their follicles. Further, ova are not produced by the million ; once every month an ovum ripens in one or other of the two ovaries, and is discharged at the surface of the ovary by the bursting of its follicle.

The oviducts are narrow tubes opening at one end into the uterus, and having at the other a broad, funnel-like expansion, which wraps round and partly encloses the ovary. Into this funnel the ova drop as they are discharged, and they are passed down the oviduct, partly by the action of cilia (chapter 3, § 5) and partly by muscular movements of the duct itself. It is curious to note an imperfection in the design of the reproductive system of most mammals ; the funnel-shaped end of the oviduct does not completely enclose the ovary, and there is, therefore, a slight risk of the discharged ovum failing to find its way into the oviduct and escaping into the general abdominal cavity. Occasionally (but fortunately very rarely) the ovum does this, and still more occasionally it is fertilized in the abdominal cavity by spermatozoa that have penetrated beyond the ends of the oviducts ; the resulting embryo implants itself somewhere among the viscera, and much danger and distress arise. Some mammals, such as the dog and ferret, are better made than we are in this respect, for they are provided with a membranous covering that encloses the ovary and is continuous with the ends of the oviducts, so that with them there is no risk of such extra-uterine pregnancy.

‘The uterus is a pear-shaped tube lying between the bladder and the rectum and having very thick walls. Itis about three inches long in its waiting state in the human subject, but its size varies with its functional condition. It has three openings; above are the very small openings -of the two oviducts, and below is the opening into the outward passage. We shall see later how the uterus encloses and nourishes the growing embryo. The uterus of the Primates (the highest mammals) when not in actual use is subjected to a regular and very stringent periodic overhaul. Once a month the