Structure of the ovary and mode of oogenesis in a freshwater crayfish, Procambarus clarkii (Girard)

The adult ovary was examined in a freshwater crayfish, Procambarus clarkii, to clarify the ovarian structure and the mode of oogenesis. A Y-shaped ova ry consisting of a pair of anterior ovarian sacs and a single posterior ova rian sac was located in the cephalothorax, on the dorsal side of the stomac h. An oviduct connected each of the posterior ends of the paired anterior o varian sacs with the genital pore on the coxa of the 6th appendage. The wal l of the ovarian sacs, consisting of a layer of the ovarian epithelium, fol ded inwards to form a number of oogenetic pouches of various sizes. Each oo genetic pouch contained one egg or large oocyte, vitellogenic or previtello genic, sometimes followed by a few early previtellogenic oocytes in the oog enetic pouch lumen. Germaria containing oogonia, very early previtellogenic oocytes and somatic interstitial cells were located in the ovarian epithel ium near the bases of the oogenetic pouches. In a cross-section of the ovar ian sac, the germaria were concentrated in the center of the ovarian sac as a central germarial cluster. An early previtellogenic oocyte beginning to grow left its germarium and raised the ovarian epithelium to form a new oog enetic pouch, in which it remained until mature. Mature eggs were ovulated from the oogenetic pouches into the central ovarian lumen, transferred into the oviducts, and oviposited through the genital pores. The female reprodu ctive system was surrounded wholly and tightly by a thin muscular sheath, w hich has often been mistaken as the ovarian epithelium in some decapod crus taceans.