The histology of the oral feeding, dorsal funnel-building, sub-anal, sensory, and respiratory tube-feet and the clavulae of the fascioles of Echinocardium cordatum is described. The penicillate tube-feet, all superficially similar, are shown to possess histological differences which reflect their function: the burrow-building tube-feet (dorsal and sub-anal), which plaster mucus on to the burrow walls, possess mucus glands surrounded by a basket work of muscle-fibres for more efficient discharge, whereas the feeding tube-feet, needing a sticky disc, have glands lacking such fibres. The sensory tube-feet lack definite discs but possess greatly enlarged subepidermal nerve plexuses. The respiratory tube-feet have a thin, much-folded wall; no nervous tissue was detected and no muscle-fibres. Each clavula has two longitudinal bands of cilia, opposite each other, on the stem and a distal knob in which mucus glands are embedded.