Follicular cysts of the ovary do not increase indefinitely with age. They are limited in growth, and in this respect differ essentially from the glandular oöphoritic cysts. They are usually about the size of a hen’s egg. They rarely attain a size greater than that of the adult fist. Exceptional cases have been reported in which the ovarian tumor was the size of the adult head. The tumor may be composed of one chief cyst-cavity, while the rest of the ovary may present a much less marked degree of cystic distention; or a large number of follicles may be uniformly distended each to the size of a cherry, forming an ovarian tumor as large as a child’s head. When the ovarian follicle becomes distended the walls usually increase in thickness and strength. The interior of the cyst is smooth. The character of the lining membrane varies with the size of the cavity. In small cysts it is the membrana granulosa--columnar epithelium. In cysts of medium size the cavity is lined with stratified epithelium. In the largest cavities there may be no epithelium present, the lining membrane being fibrous tissue. The follicular cyst is usually filled with clear serum having a specific gravity of 1005 to 1020. It resembles normal liquor folliculi. The fluid may be purulent as a result of septic infection, or it may be brown or black from the presence of altered blood. Ova are sometimes found in follicular cysts of moderate size. Sometimes hemorrhage takes place into the follicular cyst, forming a follicular blood-cyst, which may attain the size of a man’s fist. _Cyst of the Corpus Luteum._--A variety of the follicular cyst is the cyst of the corpus luteum. Such a cyst is formed by the degeneration and cystic distention of a corpus luteum. These cysts are usually of small size, rarely exceeding that of a walnut. The walls are thick and of a characteristic light-yellow color. The cavity is lined by a delicate membrane. Cysts of the corpus luteum are rare in the human female, but are very common in some of the lower animals--the cow and the mare. [Illustration: FIG. 166.--Cyst of the corpus luteum, showing the yellow lining membrane (_a_); _b_, small follicular cyst.] The _symptoms_ caused by follicular cysts are those of pressure and ovarian pain. The cyst may become impacted and adherent in the pelvis, and may cause pressure. The ovarian pain is analogous to that described under Chronic Oöphoritis. The pain that accompanies this form of cystic tumor of the ovary is much more marked than in the case of the larger kinds of ovarian cyst, which may be unattended by any ovarian pain whatever. In some cases follicular cystic disease of the ovaries is accompanied by menorrhagia or metrorrhagia which is only relieved by oöphorectomy. This symptom, however, is not usual.