Abstract
The body wall of the daughter sporocyst of Cercaria buccini has been examined by means of the light microscope, scanning and transmission electron microscopes, and the effect on the host, the carnivorous prosobranch Buccinum undatum, has been described both at the light microscopical and ultrastructural levels. The sporocyst is provided with long microvilli. Large extrusions distended by a large vesicle and with pores through which the contents of the vesicle can be released into the host tissue are found between the microvilli. The stereoscan micrographs revealed about 5 µ long cilia scattered all over the sporocyst surface; each cilium is apparently a part of a sensory structure. The tegument contains high concentrations of acid and alkaline phosphatases and small concentrations of non-specific esterase and aminopeptidase. The host tissue surrounding the sporocyst was always found in an advanced stage of histolysis. The extracorporeally digested host tissue must be absorbed through the sporocyst wall and subsequently be used by the developing cercariae.

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