HISTOLOGICAL OBSERVATIONS ON PRESUMED ELECTRORECEPTORS AND MECHANORECEPTORS IN THE BEAK SKIN OF THE LONG-BEAKED ECHIDNA, ZAGLOSSUS-BRUIJNII

Sensory receptors in the rostral portion of the beak skin of a single specimen of the rare long-beaked echidna, Zaglossus bruijnii, are desc ribed. Mucous glands which have been modified to accommodate sensory i nnervation, similar to those seen in Ornithorhynchus, are found in the rostral 2 cm of the beak skin, anterior to the maxillofacial foramen, at a density of approximately 12/mm(2). The papillary epidermal porti on of the gland ducts are walled by concentric layers of keratinocytes , and each duct is innervated by 10-15 myelinated nerve terminals. The mucous gland receptors in Zaglossus are intermediate in structure bet ween those of Ornithorhynchus and Tachyglossus, but are similar enough to the former to suggest that electroreception may play a major role in the sensory experience of Zaglossus. Push-rod mechanoreceptors also occur throughout the same region of beak skin, and appear similar to those described for Tachyglossus.