The Integument of Schistosoma Mansoni

The structure of the integument of Schistosoma mansoni is described by histochemical and electron-microscopical study, and the effects of incubating adult schistosomes in buffered saline, thyoglycollic acid, horse-radish peroxidase, normal and immune serum are described. Stage-and-sex-determined structural variations between cercariae, schistosomules, and male and female adult schistosomes are discussed. As in other trematodes, the schistosome integument consists of an enveloping, syncytial epithelium connected to subjacent cytons by internuncial processes; a similar arrangement is found in schistosome muscle cells. In cercariae, the epithelium is covered by a finely fibrillar envelope; the other stages lack any noncellular envelope or cuticle. Tubular infoldings of the trilaminate outer plasma membrane are common in all three forms and grow increasingly complex with maturation. The male plasma membrane of the gynecophoric canal is thicker than the dorsal and is pentalaminate. The cell organelles associated with protein synthesis, e.g., polysomes, and Golgi apparatus are found in the cytons, whereas the superficial syncytium shows mitochondria, multilaminate vesicles, discoid granules, spines, and dense bodies—structures presumably associated with absorptive and protective functions; thus, there is evidence of morphologic polarization. In the male dorsal integument, but not in the ventral or female integument, horse-radish peroxidase is taken up during incubation, suggesting phagocytic activity and resorption of superficial plasma membranes by multilaminate vesicles. The fine structure of the spines is paracrystalline, suggesting tightly packed, repeating macromolecular subunits. Spines are closely associated with discoid granules, but the functions of both remain unknown. The dorsal tubercles of the adult male represent herniations of medullary parenchyma through gaps in the cortical-muscle layer. Ciliated globular termini of processes of medullary cells appear in the integumental epithelium and seem to be sensory neural endings. This study is preliminary to further investigations concerning interactions at the host-parasite interface, with particular reference to the relative indifference of living schistosomes to host antibodies and cellular defense mechanisms.