A Presumed Sensory Structure Associated with the Tegument of Schistosoma mansoni

A sensory structure located in the tegument of Schistosoma mansoni adults is described. The structure consists of a bulb bearing an apical cilium which projects into the surrounding medium. The bulb apparently lies at the end of a neuron. Both the bulb and cilium are enclosed by the tegument and it is speculated that the unit may function to detect the direction of flow of the surrounding medium. In a study of the fine structure of the nervous system of the Fasciola hepatica cercaria Dixon and Mercer (1965) described a presumed tangoreceptor of apparently unique structure. A morphologically similar structure was commonly observed during an investigation of the tegument of Schistosoma mansoni and is described in this paper. MATERIALS AND METHODS Infected albino mice obtained from the Wellcome Research Laboratories, Beckenham, were killed by cervical dislocation. Worms were removed immediately and fixed both in copula and singly for 1 to 2 hr in chilled 4% glutaraldehyde buffered to pH 7.2 with phosphate. The worms were then post-osmicated for 1 to 2 hr in 2% osmium tetroxide buffered to pH 7.4 with veronalacetate. Whole worms or pairs of worms were embedded in Araldite (Luft, 1961). Thin sections were cut with glass knives on an L.K.B. ultramicrotome and mounted on bare grids. The sections were then stained for 15 min with a saturated solution of uranyl acetate in 50% alcohol and then for 5 min with lead citrate (Reynolds, 1963). The material was examined on an A.E.I. 6B electron microscope and micrographs were taken at magnifications of 5,000 to 30,000 and subsequently enlarged photographically as required.