Sensory cells in the pigeon's basilar papilla can be divided into three groups on the basis of shape, cuticular plate dimensions, and innervation. Tall hair cells are columnar with deep cuticular plates and are found over the superior cartilaginous plate from proximal to distal end of papilla; they cover the entire papilla at distal tip. Large cochlear and small efferent nerve endings terminate on their basal ends. Short hair cells are pitcher-shaped, with flattened cuticular plates and are found only on the proximal two-thirds of the free basilar membrane. They have small cochlear and large efferent nerve terminals. Transitional cells are present in between. The efferent nerve fibers, as revealed by the AChE stain, form extensive networks from which many branches are given off to the hair cells. The cochlear nerve fibers, as revealed by the Holmes silver stain, take transverse courses across the papilla with few branches before terminal ramification. Supported by N.I.H. grants Nos. NB 00966-13 and NS 08813-01.