Rostellar development in the larva of Multiceps endothoracicus (Kirschenblat, 1948).

The bladder of the larval M. endothoracicus bears several anlages which bulge in the shape of cellular buds in to the bladder cavity. A canal is differentiated from the thickened tegument which invaginates into these buds. The position of the tegument covering the bottom of the cellular anlage is more or less horizontal. The subtegumental layer is distinct. The rostellar cone differentiates from an increased number of cells situated below the tegument which covers the bottom of the canal. The tegument of the cone is covered with fine hooklets which break off gradually into the lumen of the canal. After the division of the cone into a bulb and praebulb we observed that the latter becomes overgrown by a lateral extension of the adjoining canal wall). Larger hooklets with a differently staining base were found in the thickened fold separating the praebulb from the bulb. The blade of the definitive hook differentiates from the modified tegument of this area, and from the larger hooklets after the formation of the hook organ. The lumen of the canal, and later also the spiral canal, harbour leukocytes from the tissue of the host; these attack the superficial microtrix border seen with the electron microscope. The tegument of the canal consists of a microtrix border (depth 6--7 mum), of a thick zone of distal cytoplasm with oval and rod-shaped electron dense bodies. The cytoplasm traverses the basal fibrillar membrane between the sub tegumental muscles and joins the subtegumental cells.