The fine structure of ciliated sensory cells in the epidermis of the earthworm Lumbricus terrestris.

An ultrastructural study of the earthworm body wall has revealed three types of sensory cells. Two, the multiciliate and uniciliate sensory cells, are found only in the discrete sense organs and their cilia pass vertically through the cuticle. The third type-isolated multiciliate sensory cells-are scattered throughout the epidermis and never grouped together. However, their cilia do not pass through the cuticle, but run horizontally over the outer surface of the epidermal cells. The structure of the sensory cells is described and compared with that of ordinary epidermal cells and the supporting cells found in the sense organs. Their possible physiological roles are discussed.