“…The oldest concept, that of in-situ develop- Table I. Theories on the pathogenesis of endometriosis (modified from Hingst, 1926 andRidley, 1968) In-situ development a. Germinal epithelium of the ovary (Waldeyer, 1870) b. Embryonic cell rests Mesonephric (Wolffian knob, Wolffian duct) (Von Recklinghausen, 1895, Breus, 1894 Paramesonephric (Mullerian ducts) (Cullen, 1896, Russell, 1899 c. Coelomic metaplasia (Iwanoff, 1898, Meyer, 1903, Lauche, 1923 d. Metaplasia by inflammation (Hueter, 1918, Meyer, 1919, Tobler, 1923 e. Metaplasia by hormonal stimulation (Novak, 1931) f. Metaplasia by induction (omnipotent blastema) (Levander, 1941, Merril, 1966 g. Secondary Mullerian system (Lauchlan, 1972) Transplantation a. Implantation, retrograde menstruation (Sampson, 1921) b. Implantation, mechanical transplantation (Greenhill, 1942) c. Benign lymphogenous metastasis (hystero-adenosis metastatica) (Halban, 1924/1925, Javert, 1949 Combination of in-situ development and endometrial transplantation and implantation ment, is that endometriosis develops on the spot where it is found. Development may occur from the remnants of the Wolffian ducts or the Mullerian ducts, or alternatively from metaplasia of the peritoneal or ovarian tissue (Ridley, 1968;Lauchlan, 1972).…”