Ultrastructure of oncosphere and early stages of metacestode development of Echinococcus granulosus

The ultrastructure of the oncospheres and developing metacestodes in vitro of Echinococcus granulosus was studied with emphasis on the origin of the laminated layer. The activated oncospheres measured 28 microns (S.D. = 1.83), and by day 5 of in vitro culture the metacestodes attained diameters up to 52 microns (S.D. = 2.66). The oncospheral plasma membrane of the tegument appeared to be formed by a microtubular cytoskeleton arranged in a predetermined pattern. By day 2 there were three main types of vesicles in the perikaryon: Vd, Vg1 and Vg2. Vesicles appeared to be synthesized in the perikaryon and continuously transported to the periphery, where the Vd vesicles could contribute to the ground substance of the syncytial tegument. We suggest that the Vg1 and Vg2 vesicles contribute to the laminated layer where, by day 5, they were seen in increased density and forming aggregations on the outer border.