Using standard dissecting and histological techniques, branchial nerve fibers were traced from the visceral ganglion to the ciliated epithelium of the gill of the mussel, Mytilus edulis. The pattern of activation of cilia elicited by electrical stimulation of the ganglion and the nerve, and the histological findings, indicate that individual or small groups of adjacent gill filaments are independently innervated. This would allow for discrete control of ciliary activity on different parts of the gill and agrees with the known function of the gills in filter feeding.