Mare, cow, ewe, sow, bitch, hen. Forms. Histogenesis. Dilated vesicles, egg tubes, blood obstruction. Lesions: Ovary large, smooth, lobulated, vascular, size, connective tissue, epithelium, liquid contents. Abscess. Symptoms: impaired portal circulation, muco-enteritis, piles, intestinal torpor, impaction, constriction, obstruction, congestions, inflammation. Urinary disorder. Strangulation. Sterility. Abortion. Dystokia. Indigestion. Anorexia. Colic. Genital erethism. Straining. Altered Urine. Peritonitis. Septic infection. Collapse. Rectal palpation, enlarged, sensitive ovary. _Treatment_: Castration. Tapping cyst. Rupturing cyst by compression. These have been met with in all races of domestic animals, mare, cow, ewe, sow, bitch and hen. They vary greatly in their characters, being unilocular, multilocular, rounded or lobulated, serous, albuminous, colloid or hæmorrhagic, strictly ovarian or parovarian (in broad ligaments), in one ovary or in both. _Histogenesis._ The source of these cysts has been much debated. Many have held with Spencer Wells that they have their origin in dilated Graafian vesicles, and the discovery of an ovum in the contents, by Rokitansky and Ritchie showed at least that this follicle had formed part of the cyst. On the other hand Foster, Rivolta, Klebs, Malassez and others, constantly failed to find ova or other distinct elements of the Graafian follicles, but did find epithelial elements, and note that the cysts are at an early stage connected with the surface of the ovary like the egg tubes. These embryonic tubules of Pflueger are therefore held to be the starting point for the cysts, which because of their mixed epithelial as well as liquid contents, seem allied to adenoma. From observations on the ovarian cysts of the lower animals Galtier, attaches great importance to vascular obstructions. Obstruction by pressure or otherwise led to hæmorrhages and transudation of blood, and the cavities formed in this way became the seats of epithelial growth, and liquid effusion. The blood remained for a time as distinct clots, and was later indicated by the pigmentation of the walls of the cyst.