[Morphology and zonal division of the Ductus epididymidis of rats. II. Electron microscopic investigations (author's transl)].

The light microscopical zonal division of the ductus epididymidis of adult rats is substantiated and extended by ultrastructural differences of the epithelial cells lining the duct. The principal cells are rich in endocytotic vesicles and possess a well-developed Golgi apparatus in all 9 zones of the duct. Polymorphous lysosomes, however, preferentially occur in the principal cells of zone 4-7; the principal cells of zone 1-3 and 8-9 contain other types and less numerous lysosomes. The rough endoplasmic reticulum (ER) and possible exocytotic vesicles and vacuoles predominate in the principal cells of zone 1-3 and the smooth ER in those of zone 7. The clear cells are always poor in microvilli and contain different amounts of vacuoles, vesicles, lipid and lipoid droplets and lysosomes. Light droplets and lysosomes are typical for the clear cells of zone 5, dark droplets for those of zone 6; the clear cells of zone 7 possess many dark droplets and lysosomes; and in zone 8 and 9 these cells contain numerous vesicles, vacuoles and lysosomes. The apical cells belong to the group of principal cells; in addition, bottle shaped-cells (narrow cells), basal clear cells and 2 populations of intraepithelial leucocytes exist; the leucocytes leave the blood capillaries, penetrate the epithelium and enter the lumen of the duct. If, in addition, enzyme histochemical and experimental data are respected the principal and clear cells are involved in zonal specific absorptive processes but perhaps also in secretion processes into the lumen of the duct, the clear cells of zone 5 and 6 may be responsible for the secretion of hydrolases present in the sperm plasm. Clear signs for endocrine secretion are not seen; at least some of the leucocytes may represent immunocompetent lymphocytes which seem to be not identical with those in the epithelia of other organic systems.