Cysts of the placenta have been reported by Millet and others, supposed to have developed from the exudation of blood forming a clot separating the chorion, usually of small size, and in some cases more than one is noted. Ercolani reported two cases; in one the entire fetal surface of the placenta was sown with round tumors covered by chorion—the largest being about the size of a cherry. Some have been opened and the chorionic wall torn, showing a solid material filling the depth of the cyst; others were more solid, and were filled with coagulated fibrin, in which rounded masses of granular hematin could be seen. Ercolani proved that the interior wall was formed by the chorion, which covered the whole bloody mass, of which half projected above the placental surface, while half dipped into the placental tissue, and lay in immediate contact with the effused blood. The term