It has been observed by Sampson1 that in women between the age of 30 and the menopause a frequent pathologic condition is found which consists in part of the presence of "chocolate" cysts of the ovary. These cysts are lined with ciliated epithelium, are surrounded by stroma like that of the endometrium, and take part in the menstrual cycle in much the same manner as does the uterine mucosa. When a cyst is close to the surface of the ovary, it may, and frequently does, rupture during menstruation, scattering, in the pelvic cavity, epithelial cells of the type lining the cyst and also menstrual blood. The menstrual blood possibly contains a substance which is capable of so altering the peritoneum that the epithelial cells from the cyst may become implanted where the peritoneum is injured, and develop, producing adenoma-like growths; or these cells may invade, from the outside, such