Development of the tegument of Echinococcus granulosus (Cestoda) protoscoleces during cystic differentiation in vivo.

During the first 4 days following infection, early tegumentary changes are confined to the protoscolex soma of Echinococcus granulosus, the thick glycocalyx being lost and the blunt elevations, flattened. The Golgi complexes within the tegumentary cytons produce T2 vesicles that increase in number in the tegument from days 4 to 12, whereas T1 vesicles decline. Spineless, truncated microtriches develop at the somal surface, and the laminated layer starts to form around the developing cyst from days 20-40 onwards. T2 vesicles do not appear to be involved in its formation and decline in number. Two additional vesicle types participate in the production of the laminated layer: T4 vesicles contribute to the carbohydrate matrix, and 'G' vesicles form granular accumulations. Cystic differentiation is completed after 2-3 months, when the spined microtriches and rostellar hooks of the scolex are shed into the laminated layer and replaced by truncated microtriches. These ultrastructural changes are discussed with respect to parasite survival.