Distribution and Anatomy of Lateral Line Organs in the Tail of the Mudpuppy

Abstract

Lateral-line organs, sensitive to water displacement, are found abundantly on the head, trunk, and tail of the larval amphibian, Necturus maculosus. The organs occur along the tail in small linear groups, called stitches, which run rostrocaudally. Each organ consists of a bulb-shaped structure, embedded in the skin and composed of a central group of eight to 10 hair cells surrounded and separated by supporting cells, and of a long narrow cupula extending from the skin surface several hundred microns into the water. Eighty microns long and 20 μ in diameter at the base, with a narrow neck extending to the surface, the hair cell in the mudpuppy lateral-line organs is several times as large as those found in most other animals. Thirty to 40 stereocilia and a single asymmetrically placed kinocilium project from the apical end into the cupular substance. In approximately half the hair cells of each organ, the kinocilium is located toward the caudal side of the cell and in the remainder toward the rostral side. Each stitch is innervated by two large myelinated afferent nerve fibers that branch to all its organs. Knoblike afferent endings, characterized presynaptically by synaptic bodies and surrounding vesicles, terminate at the base of each hair cell.