The present study was carried out to describe the ovary and oogenesis in the freshwater bivalve Caelatura parreyssi from
histological and ultrastructural points of view. Ten adult healthy clams collected from the River Nile were used in this study. The specimens were dissected and gonads were obtained and processed for histological and ultrastructural examination. Histologically, the ovary of C. parreyssi is composed of numerous of follicles which are connected together by connective tissue. Each follicle contains different stages of developing oocytes; oogonia, previtellogenic
oocytes, vitellogenic oocytes and postvitellogenic oocytes (mature oocytes). At ultrastructural level, stages of female gametogenesisvwere examined; the process of oocytes formation and yolk deposition were described in successive stages of oogenesis. The structure and function of auxiliary cells and follicle cells in ovarian follicles during vitellogenesis were discussed. In conclusion, this study showed that the follicle cells play an important role during oogenesis but probably are not the major source of yolk precursors. The vesicular connective tissue is probably the main source of nutrients for vitellogenesis. The auxiliary cells appear to play an integrate role in the development of the oocytes as their functions
can permit a transfer of precursors necessary to vitelogenesis.