“…Observations that the administration of progestogens to rodents during early pregnancy induces virilization of the foetal genital tract (Mey & Scheid, 1959;Revesz, Chappel & Gaudry, 1960;Falconi, Gardi, Bruni & Ercoli, 1961;Schöler & de Wächter, 1961;Lerner, de Phillipo, Yiacas, Brennan & Borman, 1962;Neumann, Kramer & Junkmann, 1964;Junkmann, 1964;Suchowsky, Turolla & Arcari, 1967) comparable to that produced by androgens, have prompted the present study of the histological changes induced in the embryonic development of the mammary gland by the administration of certain progestogens.…”