[On the ultrastructure of the cysticercoid of Hymenolepis stylosa (Cestoda: Cyclophyllidea) (author's transl)].

Electron microscopy of the tegument of H. stylosa cysticercoid as compared with that of H. diminuta reveals great variations in the fine structure of the larval tegument of these two species. On the scolex and the inner cyst wall, the tegument of H. stylosa cysticercoid bears typical microtriches; at the level of the anterior pore, the microtriches are flexuous. The tegument of the outer cyst wall appears as a syncytial band with dense material which accumulates in the region below the unit membrane, and the tegument of the cercomer is increased by branchied microvillies. While, the scolex of H. diminuta cysticercoid is unarmed and the tegument of the outer cyst wall bears branched microvillies. The data permit the conclusion that the differentiation of tegumental structures is graduated from the scolex to the cercomer. This differenciation is more or less important according to the parasite and results of successive inductions which affect parts of the cysticercoid. The significance of these findings is discussed in terms of the possible function of these structures and the penetration of substances.