Sequential morphological study of teratomas derived from displaced yolk sac.

The sequential histological and ultrastructural morphology of benign teratomas derived from displaced visceral yolk sac is described. The appearance and the differentiation of all the tissues formed in these teratomas is compared to the differentiation of normal embryonic tissues and to the development and differentiation observed in experimental teratocarcinomas. The presence in the teratomas of adult well-differentiated tissues derived from all three germ layers is discussed in relation to the multipotentiality of cells from the extra-embryonic parts of the embryo.