In this study the ovarium, ovarian wall and oviduct of Asellus aquaticus ( A. aquaticus) (Crustacea: Isopoda) were investigated by stereomicroscopy, phase contrast microscopy and light microscopy. Long, tube-shaped, separate ovaries of A. aquaticus are located dorsolateral to the gut. The germinal zone is confined to the ventral region of the ovary as a thin band. The ovarian wall is composed of a few fibrous layers. The oviduct is located in the anterior one-third of the ovary, not in the central part. The sheath of the oviduct was found to possess some muscle cells, a feature first noted in this study. They appear to be different from the striated muscles of vertebrates, and are characterized by abundant cytoplasm, typical striated muscle bands and the absence of sarcoplasmic reticulum owing to their presence in a confined region of the oviduct sheath. It is suggested that the muscle cells act as a sphincter and provide elasticity which prevents tearing of the oviduct during discharge of eggs from the ovarium.

In this study the ovarium, ovarian wall and oviduct of Asellus aquaticus ( A. aquaticus) (Crustacea: Isopoda) were investigated by stereomicroscopy, phase contrast microscopy and light microscopy. Long, tube-shaped, separate ovaries of A. aquaticus are located dorsolateral to the gut. The germinal zone is confined to the ventral region of the ovary as a thin band. The ovarian wall is composed of a few fibrous layers. The oviduct is located in the anterior one-third of the ovary, not in the central part. The sheath of the oviduct was found to possess some muscle cells, a feature first noted in this study. They appear to be different from the striated muscles of vertebrates, and are characterized by abundant cytoplasm, typical striated muscle bands and the absence of sarcoplasmic reticulum owing to their presence in a confined region of the oviduct sheath. It is suggested that the muscle cells act as a sphincter and provide elasticity which prevents tearing of the oviduct during discharge of eggs from the ovarium.