Abstract
Spontaneous ovarian teratomas in mice (LT/Sv and LT/SvXBJ) and experimental teratomas (the result of blastocyst transplantation underneath a testicle capsule of CBAXC57 mice) are represented with derivatives of three germ layers. During the process of cytodifferentiation, the epithelium of various origins forms closed cavities (cysts), whereas in more complex morphogenetic processes, the epithelium participates in reduced organogenesis. Intestine analogs have been reported in spontaneous and experimental teratomas, but skin analogs have been shown only in experimental teratomas. The mitotic activity of lining epithelia of organ analogs differs significantly from karyokinetic figures of similar epithelia in cysts. Possible reasons for this phenomenon are discussed in this paper.