Structure of the ovary and mode of oogenesis in a freshwater crab Potamon dehaani

Structure of the adult ovary and oogenetic mode were examined in the freshw ater crab Potamon dehaani. An II-shaped ovary consisting of a pair of long ovarian sacs connected by a narrow bridge tube is located in the cephalotho rax on the dorsal side of the stomach. A short oviduct with a seminal recep tacle is connected with the posterior end of each ovarian sac, and a genita l pore opens on the sternum of the sixth thoracic segment. The ovarian wall consists of a layer of ovarian epithelium that infolds to form a number of oogenetic pouches of various sizes. These are present mainly in the anteri or regions of the ovarian sacs, are scarce in the posterior regions of the ovarian sacs, and are absent from the bridge tube. Each oogenetic pouch con tains an egg or a relative large oocyte in its lumen. Germaria containing o ogonia, very early previtellogenic oocytes, and somatic interstitial cells are located in the ovarian epithelium near the necks of the oogenetic pouch es in the anterior regions of the ovarian sacs and are randomly scattered t hroughout the ovarian epithelium in the posterior regions of the ovarian sa cs. In cross section, the germaria appear to be concentrated into a central germarial cluster in the ovarian sac. In the posterior regions of the ovar ian sacs, however, the germaria are randomly scattered throughout the ovari an epithelium. An early previtellogenic oocyte leaves its germarium and rai ses the ovarian epithelium infolds to form a new oogenetic pouch in which i t grows to maturity. Mature eggs are ovulated from the oogenetic pouches in to the ovarian lumen, transferred from the ovarian lumen into the oviducts, fertilized there by sperm stored in the seminal receptacles, and then ovip osited through the genital pores. The female reproductive system is surroun ded wholly and tightly by a thin, cellular, membranous sheath, which has of ten been mistaken as the ovarian epithelium in some decapod crustaceans. (C ) 1999 Wiley-Liss, Inc.