The wall of the spermathecal ampulla in Tubifex tubifex consists of epithelial, muscular and peritoneal layers. The epithelial surface contains closely microvilli while lateral and basal plasma membranes are extensively convoluted. Epithelial cytoplasm exhibits a vertical zonation of subcellular components. The distal zone contains filiform secretory particles which are orientated perpendicular to the apical surface; extrusion occurs by their fusion with the plasma membrane between the bases of neighbouring microvilli. Mitochondiral and Golgi zones, the latter containing the nucleus, subtend the distal zone. The basal zone, composed of vertical compartments formed by the folded plasma membrane, is rich in α-glycogen rosettes. The distal epithelium and lumen material contain neutral mucopolysaccharides and carboxylated acid mucopolysaccharides in conjunction with neutral protein. The ultrastructure of the spermathecal duct wall is comparable with that of the ampulla but is characterized by extremely long microvilli and a prominent musculature.