1. The dorsal epithelium consists of flattened polygonal cells with various surface modifications including ruffles, microvilli-like projections, and small protruding vesicles. A double ridge arises where adjacent cells meet. The refractile lipid globules reach almost to the surface not by a pore, but by a slit between adjoining cells. There is some suggestion that the globules might be discharged through the slit. 2. In both epithelia, the flagellum arises from an excentrically located ciliary pit. In the dorsal epithelium, the inner wall of the pit is connected to the basal portion of the flagellum by radiating filaments. In both epithelia, the flagella may bear ‘hoods’ as localized bulges in restricted areas. Their role is still unknown. 3. Attached food organisms are found both on the ventral and the dorsal surface. The latter might function in food capture. 4. Surface views of the fiber cells of the intermediate layer reveal many branched extensions and intercellular connections. The number of connections must far exceed the cell number of this layer and is thought to be instrumental in coordination. 5. The bulging margin ofTrichoplax may contain a space of its own.