Simple ovarian dermoids are usually of small or moderate size, varying from the size of a hen’s egg to that of the adult head. The cysts rarely contain more than 8 pints of fluid. Dermoid cysts may become larger by fusion with glandular cysts or as the result of inflammation. Dermoid cysts are usually unilateral; both ovaries are affected in about 20 per cent. of the cases. They are primarily unilocular. Sometimes two or more dermoid cysts spring from the same ovary, and these contemporaneous cysts may become united, and the contiguous walls may atrophy so that the cavities communicate. Dermoid cysts of the ovary have been found at all ages--in the fetus of eight months and in women over eighty years of age. They are observed most frequently from the fifteenth to the forty-fifth year. The external appearance of the dermoid cyst differs from that of the glandular cyst. It is dull and often yellowish or brownish in color. Upon the internal surface of the cyst is found a membrane which looks like skin and which has a similar structure. The skin may cover the whole of the surface of the cavity, or it may be restricted to a small area, and with the underlying tissue form a prominence of the cyst wall--the so-called parenchyma body. This body is composed of tissue derivatives of one, two, or all three layers of the blastoderm from the surface inward--the ectoderm, mesoderm, and entoderm. The following cutaneous appendages are found: hair, sebaceous glands, sweat-glands, teeth, mammæ, horn, nails. The cyst may also contain bone, unstriped muscle, and tissue resembling brain-matter. The hair may arise from the whole surface of the cyst, or tufts of various length may be found growing from slight prominences of the surface. The hair is usually short; it is sometimes found, however, varying in length from 4 or 5 inches to 5 feet. There seems to be no relation between the color of the hair of the dermoid and that upon the external surface of the body of the individual. The hair in an ovarian dermoid of a negress has been found of a blonde color. The hair changes in color with age, and in an old woman may become white. The hair is constantly shed, and the cyst may contain a large quantity of short loose hair mixed with the other contents. Sometimes the shed hair is found rolled up in balls of sebaceous matter. Sebaceous glands and sweat-glands are usually numerous. Teeth may be found free in the cyst-cavity, or they may be attached to bone or cartilage within the cyst-wall, while the crowns project into the cavity; or they may lie completely imbedded in the wall. They are often well formed, though they may be faulty in development and shape. They are usually few in number, ranging from one to ten. Many more teeth than this, however, are sometimes found; in one case there were 300.