ovary, instead of lying inside of the Müllerian duct, as it does at first, finally lies behind and below the tube.

FIG. 6.-Internal Genitalia of a Human Fetus, 9 cm. long (enlarged 8 times): H, testicle; E, epididymis (epididymal part of Wolffian body); U, organ of Giraldez (uropoetic part of Wolffian body); G, bundle of connective tissue containing vessels; Y, vas deferens (Wolffian duct) (Waldeyer).

FIG. 7.-Internal Genitalia of a Human Female Fetus, 9 cm, long (enlarged 10 times); 0, ovary; T, tube; O abd., abdominal ostium of tube; E, parovarium; U, uropoetic part of the Wolffian body remaining as tubes between parovarium and uterus; Y, Wolffian duct disappearing lower down; Mp., Malpighian bodies (Waldeyer).

The ovarian vessels enter originally at the upper end of the

Transverse Section of Ovary of Human Embryo of three months (enlarged 43 times): a, mesoarium; a', stroma of the hilum (medullary substance); b, glandular tissue (cortical substance) (Kölliker).

mesoarium from the posterior wall of the abdomen, and are enclosed in a fold of the peritoneum, which in the course of time becomes the infundibulo-pelvic ligament, extending from the fimbria of the tube to

Transverse Section through the Ovarian Region of a Human Embryo of five months; lower surface seen from above (enlarged 3 times): oi, os ilium; 8, sacrum; mo, mesoarium and hilum of ovary, bounded by two lips; o, cut surface of the ovary; v, free ventral surface, or lateral part of the ventral surface, of the ovary; m, rectal surface of ovary, or medial part of its ventral surface; t, tube; mt, mesentery of tube (later ala vespertilionis); r, rectum; u, uterus; ur. ureter; au, umbilical artery; ie, external iliac vessels; nc, anterior crural nerve (Kölliker).

the wall of the pelvis. To the outer side of the mesoarium is attached the mesosalpinx (Fig. 9), or mesentery of the tube, which later is called

Ovary of a Human Fetus of ten or eleven weeks: a, superficial stratum of cells: b, layer of connective tissue; c, trabeculae of connective tissue, the cells having been removed; d, mesoarium; e, part near surface seen with higher power; n, natural size of the specimen (H. Meyer).

ala vespertilionis (the bat's wing), and contains the remnants of the Wolffian body, especially the parovarium, but at this period has no connection with the uterus.

The Formation of Ova and Graafian Follicles.-At the earliest stage the ovary is represented by a mass of cells developed from the peritoneal cover of the Wolffian body, and soon a protuberance of connective tissue enters from behind into this cell-mass. These two elements build up the whole ovary, the cells forming the parenchyma, or glandular element, and the connective tissue the stroma. Pro

FIG. 12.

Part of Ovary near Surface, from Human Fetus of twenty-eight weeks. In some places appears the permanent epithelium, composed of a single layer (H. Meyer).

Part of Ovary near Surface, from a Human Fetus of thirty-six weeks. The single layer of epithelium is interrupted by a belated primordial ovum with its follicular epithelial cells (H. Meyer).

longations from the connective tissue grow in between the cells and separate them, forming groups, and grow together over them; but from this cover new prolongations start, and new cells are constantly formed on the surface (Fig. 10). In this way irregular tubes filled

with cells are formed which connect with one another, much like the canals found in a sponge (Figs. 11, 12, 13); but finally the whole surface is only covered by a single layer of cells, the columnar epithelium, under which is found a layer of connective tissue, the albuginea, and under that we find clusters of cells surrounded by connective tissue (Fig. 14), or sometimes a long row of large cells, each

Part of Section from Surface to Hilum of Ovary of Girl three days old: 8, single layer of epithelium yet in connection with cluster of primordial ova. All ova have disappeared from the surface. A broad layer of stroma separates in most places the epithelium from the follicular zone. The farther we go from the surface toward the hilum, the fewer ova are there in one nest, until, finally, there is only one in its primary follicle; n, natural size of the whole ovary (H. Meyer).

surrounded by smaller cells, until finally all these clusters and columns are broken up into small compartments, each containing one

large cell and one or more smaller ones (Fig. 15). The large cells have each a large nucleus and nucleolus, and are the future ova, and

Perpendicular Section through the Ovary of a Bitch of six months (Hartnack, 3): a, the epithelium; b, epithelial pouch opening on the surface; c, larger group of follicles; d, ovarian tube filled with ova; e, oblique and transverse sections of ovarian tubes (Waldeyer).

are called primordial ova; and the small cells multiply and form the epithelium of the primary follicles, which are the beginning of the

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FIG. 16.

Three Graafian Follicles from the Ovary of a New-born Girl (enlarged 350 times): 1, natural condition; 2, treated with acetic acid; a, structureless membrane; b, epithelium (membrana granulosa); c, yolk; d. germinal vesicle, with germinal spot; e, nuclei of the epithelial cells; f, vitelline membrane (Kölliker).

Graafian follicles (Fig. 16).

The small cells increase in number and form several layers. A fissure is formed between them, and a fluid accumulates in this space, the beginning of the future liquor folliculi. The outer layers form the epithelium of the Graafian follicle, the so-called membrana granulosa; the inner continue to surround the ovum, forming the discus proligerus (Fig. 17). The fibrous membrane of the follicles is formed by a differentiation of the surrounding stroma.

It will be seen from the above description that the ova, the surface epithelium of the ovary, and the epithelium of the Graafian follicles have all one common origin, the cellular mass formed on the inner edge of the Wolffian body. As mother to so many epithelial formations, this is called the germ-epithelium. The formation of ova on the surface of the ovary ceases from the time the single layer of epithelium is formed, about the end of the seventh month, but it seems that the ova themselves multiply by division.