The ovary is unaffected unless the cyst be of very large size, in which case the ovary may be stretched upon the surface of the cyst, so that its position becomes difficult to determine. There are two varieties of parovarian cyst--the simple and the papillomatous. The _simple parovarian cyst_ has a very thin wall of uniform thickness. In small cysts, less than the size of a child’s head, the wall may be transparent. It is of a light yellowish or greenish color, and the fine vessels ramifying upon the surface are plainly visible. As one would expect from the direction of growth, the outer covering of the cyst is peritoneum, which is not adherent and may be readily stripped off. The middle coat is composed of fibrous tissue containing unstriped muscle. The lining membrane is ciliated columnar epithelium, stratified epithelium, or simple fibrous tissue, according to the size of the cyst. The changes in the character of the epithelium are due to pressure. The cyst-contents are a clear, limpid, opalescent fluid of a specific gravity below 1010. In the _papillomatous parovarian cyst_ the interior is covered with warts or papillomatous growths resembling in every respect those that occur in the cyst of the paroöphoron, already described. The papillomatous parovarian cyst exhibits the same clinical features, and is liable to the same accidents, as the paroöphoritic cyst. It may become perforated and infect the general peritoneum. The walls of the papillomatous parovarian cyst are somewhat thicker than those of the simple parovarian cyst; the fluid contents are not so clear and limpid, and may contain altered blood that has escaped from the papillomata. Parovarian cysts are almost invariably unilocular. Only a few cases have been reported in which two or more cavities were present. The cysts are of small size, not often exceeding that of a child’s head. They may, however, attain large dimensions and contain several quarts of fluid. Parovarian cysts are of very slow growth, and refill but slowly after tapping or rupture. On account of the thinness of the cyst-walls, these cysts seem especially liable to the accident of rupture. Unless the cyst be papillomatous, the bland, unirritating fluid is readily absorbed by the peritoneum, and the cyst may remain quiescent for a long period. Cysts of the parovarium occur most frequently during the period of active sexual life. Unlike dermoids and cysts of the oöphoron, they are unknown in childhood. Cysts of the parovarium are much less common than cysts of the oöphoron and paroöphoron. In 284 tumors of the ovary and parovarium operated upon by Olshausen, about 11 per cent. originated in the parovarium. Some authorities maintain that in rare instances dermoid cysts may arise from the parovarium.