Cell contacts between follicle cells and the oocyte of Helisoma (Mollusca, Pulmonata)

The cell contacts between follicle cells, and follicle cells and oocytes of egg‐laying populations of Helisoma duryi and non‐egg‐laying populations of H. trivcolvis have been studied. Scanning electron microscopy reveals that four to six follicle cells envelop a single developing oocyte. Thin sections and lanthanum impregnations demonstrate apical zonulae adherentes followed by winding pleated‐type septate junctions between follicle cells. Gap junctions and septate junctions have been found between follicle cells and vitellogenic oocytes. Freeze‐fracture replicas show relatively wide sinuous rows of septate junctional particles, and nemerous large gap junctional particle aggregates on the P‐face between vitellogenic oocytes and follicle cells. Septate and gap junctions between immature or nonvitellogenic oocytes and follicle cells are fewer compared to those in vitellogenic oocytes. Similarly, the junctional complexes are less developed in non‐egg‐laying H. trivolvis compared to those in egg‐laying H. duryi . It is possible that intimate interaction between follicle cells and a developing oocyte is necessary for the maturation of the oocyte. The junctional complexes could be involved in the interaction of the follicle cells and the oocyte, and they must disassemble at the onset of ovulation. Rhombic particle arrays and nonjunctional ridges of particles have been found in the basal part of the oolemma.