rods, thus giving rise to 12 groups of 4 chromosomes, or 12 tetrads. The mother cell now divides into 2 unequal parts, the process consisting in a distribution of the rods composing the tetrads in such a way that the pairs of rods derived from one set of daughter loops pass to the one daughter cell, and those derived from the other set to the second daughter cell. In this manner are formed the large egg daughter cells (O. Hertwig) or oocytes of the second order, and a smaller cell, the first polar body. From this it is seen that the daughter cell still retains 12 pairs of rods. A second unequal division immediately follows without a period of rest, but in this case the component parts of the pairs of rods are so divided that each separate rod moves away from its fellow, although they both originated from the same daughter loop. In this manner a cell of the third generation is formed, the oocyte of the third order, or mature ovum, as well as a second polar body. The second division in the period of maturation is peculiar in that here daughter chromosomes are formed, not by a longitudinal splitting of the chromosomes, but by a transverse division.

In the process of development of the ova, three periods are therefore distinguishable. The first, or period of proliferation, represents a stage of repeated mitotic division in the oogonia, during which the latter become gradually reduced in size. In the second, or period of growth, the oogonia increase in size and are then ready for the third, or period of maturation. In the latter, by means of a modified double mitotic division, uninterrupted by any resting stage, the matured ovum and the polar bodies are formed. several periods are represented in figure 265.

These

The manner in which the fully developed Graafian follicle bursts and its ovum is freed is still a subject of controversy; the following may be said regarding it: By a softening of the cells forming the pedicle of the discus proligerus, the latter, together with the ovum, are separated from the remaining granulosa, and lie free in the liquor folliculi. At the point where the follicle comes in contact with the tunica albuginea of the ovary, the latter, with the theca folliculi, becomes thin, and in this region, known as the stigma, the blood-vessels are obliterated and the entire tissue gradually atrophies; thus a point of least resistance is formed which gives way at the slightest increase in pressure within the follicle, or in its neighborhood.

The increase of pressure within the follicle, leading to its rupture, is, according to Nagel (96), due to a thickening of the tunica interna of the theca of the follicle. The cells of this layer proliferate and increase in size and show yellowish colored granules. This cell-proliferation leads to a folding of the tunica interna, the folds encroaching on the cavity of the follicle, and causing its contents to be pushed toward the stigma.

When the ovum is released, the rest of the follicle remains behind to form a corpus luteum. In the formation of the much larger

corpus luteum verum-i. e., one whose ovum has been fertilized and is in process of further development-the regressive metamorphosis is much slower than is the case with the corpora lutea spuria, whose ova have not been impregnated. In place of the liquor folliculi the corpus luteum usually contains a blood coagulum which is formed as a result of the rupture of the adjacent blood-vessels. Then follows a proliferation of the tissue composing the tunica interna of the theca folliculi. This ingrowth gradually surrounds and finally penetrates into the coagulum and the few granulosa cells remaining, while the latter degenerate and are eventually absorbed. The proliferating tissue contains cells filled with pigment, the lutein cells, and it is these which give rise to the characteristic yellow color of the bodies. The inner wall of the corpus luteum is gradually folded in and the

Fig. 265.-Scheme of the development and maturation of an ascaris ovum (after Boveri): P. B., Polar bodies. (From "Ergebn. d. Anat. u. Entw.," Bd. I.)

degenerating central portion is finally penetrated by vessels and absorbed by the proliferating cells from the outer wall. In the folds of the tunica interna, composed of lutein cells, there is found a variable amount of fibrous connective tissue carrying blood-vessels which break up into capillaries, the latter penetrating between the lutein cells.

According to Sobotta (96 and 97), the corpus luteum of both the mouse and the rabbit is formed chiefly by a hypertrophy of the epithelial cells, while the vascular connective tissue of the inner thecal layer penetrates between the epithelial cells in the shape of processes accompanied by leucocytes, which form a cellular network around the central coagulum. The blood is finally absorbed

without the formation of hematoidin crystals, and a mucoid connective-tissue mass is the result. There is then no further proliferation of connective tissue and the corpus luteum is fully developed in this condition. Later, fat globules are deposited in the greatly enlarged epithelial cells. In the mouse there is no difference as to structure or size between corpora lutea derived from follicles whose ova have been impregnated and those whose ova have not been fertilized.

After a variable time the tissue of the corpus luteum itself undergoes hyaloid degeneration, a process which may be compared to the formation of scar tissue, and which finally results in the formation of the corpus albicans. The latter is then in its turn

Fig. 266.-Section of fully developed Graafian follicle from injected ovary of pig;

X 50.

absorbed, and in the end there remains in its place only a connective tissue containing very few fibers.

Not all of the eggs and follicles reach maturity; very many are destroyed by a regressive process known as atresia of the follicles. This process may begin at any stage, even affecting the primitive ova while still imbedded in the germinal epithelium-first attacking the egg itself and later the surrounding follicular epithelium, although in both the degenerative process is identical. The germinal vesicle and the nuclei of the follicular cells usually undergo a chromatolytic degeneration, although they sometimes disappear without apparent chromatolysis (direct atrophy), while

the cell-bodies are generally subjected to a fatty degeneration or may even undergo what is known among pathologists as an albuminous degeneration-i. e., one characterized by granulation and showing no fat reaction but numerous reactions such as are observed where albumin is present. These two forms of metamor

phosis result in a liquefaction of the cell-body, and finally lead to a hyaline swelling, which renders the substance of the cell homogeneous. The zona pellucida softens, increases in volume, becomes wrinkled, and after some time is absorbed. A further stage in the regressive process consists in the formation of scar tissue, as in the case of the corpus luteum. Here leucocytes accompany the proliferation from the tunica interna of the theca folliculi, and assist in absorbing the products of degeneration, the result being a connective-tissue scar (vid. G. Ruge, and Schottländer, 91, 93).

The blood-vessels of the ovary enter at the hilum and branch in the medullary substance of the ovary. From these medullary vessels branches are given off which penetrate the follicular zone, giving off branches to the follicles and terminating in a capillary network in the tunica albuginea (Clark, 1900). The relations of the branches to the follicles are such that in the outer layer of the theca folliculi the vessels form a network with wide meshes while the inner layer contains a fine capillary network (Fig. 266). The veins are of large caliber and form a plexus at the hilum of the

ovary.

The lymphatics of the ovary are numerous. They begin in clefts in the follicular zone, which unite to form vessels lined by endothelial cells in the medulla. They leave the ovary at the hilum.

The nerves accompany and surround the blood-vessels, while very few nerve-fibers penetrate into the theca folliculi; those doing so form a network around the follicle and end often in small nodules without penetrating beyond the theca itself. Ganglion cells of the sympathetic type also occur in the medulla of the ovary near the hilum (Retzius, 93; Riese, Gawronski).

3. THE FALLOPIAN TUBES, UTERUS, AND VAGINA. The Fallopian tubes consist of a mucous membrane, muscular coat, and peritoneal covering.

The mucous membrane presents a large number of longitudinal folds which frequently communicate with one another. Very early in the development four of these folds are particularly noticeable in the isthmus; these may also be recognized at times in the adult. These are the chief folds, in contradistinction to the rest, which are known as the accessory folds (Frommel). The accessory folds are well developed in the isthmus, and are here so closely arranged that no lumen can be seen with the naked eye. The epithelium lining the tubes is composed of a single layer of ciliated columnar

cells which entirely cover the folds as well as the tissue between them. Glands do not occur in the oviducts, unless the crypts between the folds may be considered as such. The mucosa beneath the epithelium contains relatively few connective-tissue fibers, but numerous cellular elements. In the isthmus it is compact, but in the ampulla and infundibulum its structure is looser. The mucosa contains a few nonstriated muscle-fibers, which have a longitudinal direction and extend into the chief folds, but not into. the accessory folds.

External to the mucosa is found the muscular coat, consisting of an inner circular and an outer and thinner longitudinal layer. The latter is imperfectly developed in the ampulla and may be

Fig. 267.-Section of oviduct of young woman. To the left and above are two enlarged ciliated epithelial cells from the same tube; × 170.

entirely absent in the infundibulum. The peritoneal layer consists of a loose connective tissue covered by mesothelium.

The uterus is composed of a mucous, a muscular, and a peritoneal coat.

The mucosa of the body of the uterus and cervix is lined by a single layer of columnar ciliated epithelial cells; these are somewhat higher in the cervix than in the corpus. Barfurth (96) has found intercellular bridges between the cells of the uterine epithelium in the guinea-pig and rabbit. In the cervix of the virgin the ciliated columnar epithelium extends as far as the external os, at which point this usually changes to a stratified squamous epithelium. In