For many years they have been a mystery to physiologists, and their origin now is little more than hypothetic.

At one time the fact of finding such a formation in the ovary of an unmarried woman was presumptive evidence that she was unchaste; but this idea was dissipated as soon as examples were reported in children, and to-day we have a well-defined difference between congenital and extrauterine pregnancy.

Dermoid cysts of the ovary may consist only of a wall of connective tissue lined with epidermis and containing distinctly epidermic scales which, however, may be rolled up in firm masses of a more or less soapy consistency; this variety is called by Orth epidermoid cyst; or, according to Warren, a form of cyst made up of skin containing small and ill-defined papillae, but rich in hair follicles and sebaceous glands.

Even the erector pili muscle and the sudoriparous gland are often found.

The hair is partly free and rolled up into thick balls or is still attached to the walls.