The differentiation and involution of the müllerian duct in the rat.

The structural differentiation of the Müllerian ducts of both sexes was studied in rat fetuses from 15 to 21 days of gestation. Differences between the male and female Müllerian ducts were observed from the 17th day onward. The epithelium of male Müllerian duct lost its regular arrangement, the increased lysosomal activity and disintegration of some cells was found. The involution of the male duct was accompanied by the condensation of the surrounding mesenchyme with the participation of macrophages. The female Müllerian duct was lined with simple columnar epithelium; its pattern remained indifferent until birth. The apical migration of centrioles and solitary cilia formation belonged to the typical findings from the 18th day. Neither ciliated cells nor multiple centriole replication were observed in oviductal segment of Müllerian duct.