Structures of ovary and ovarian follicle in flathead lobster,Thenus orientalis (Lund, 1793) (Crustacea: Decapoda: Scyllarida)

The ovary contains four morphological components : (1) the ovarian wall, (2) therepro ductive epithelium, (3) the cellular layer containing oocytes, oogonia (especially for early-developing ovary) and follicle cells, and (4) the extensions of the ovarian wall. The ovarian wall and its extensions consist of blood vessels, sinuses, muscle cells and others. The extensions of the ovarian wall project into among the follicles and insert on the thick basal membrane of each follicle.From inside to outside, the follicles are composed of four parts: (1) the oocyte, (2) the perivitelline space, (3) the follicle cells, and (4) the basal membrane. The surface of the oocyte during vitellogenesis is folded into numerous long microvilli that project into the perivitelline space between the oocyte surface and the bace of the follicle cell layer. In addition, the plasma membrane of the vitellogenic oocyte contains many pinocytotic pits. The perivitelline space is engorged with more electrondenser material as the development of the follicle. The inclusion of perivitelline space in the mature follicle is named specially as the chorion. The chorion is composed of two region, a thinner exochorion and a thicker endochorion containing electron-dense granular material. The follicle cell layer is composed of a single layer of polygonal follicle cells which exhibit higher synthetic activity. The synthetic product of the follicle cell layer is one source for the inclusion of the perivitelline space.The structures of the ovary and ovarian follicle in T. orientalis show that the exogenously biosynthetic yolk plays important roles in the vitellogenesis.