The structure of stretch receptor endings in the fin muscles of rays

Abstract

The muscles of the paired fins of rays have long been known to possess large sensory endings of a special type, first described inTorpedoby Poloumordwinoff (1898) and Cavalie (1902), and subsequently re-examined by Barets (1956). They consist of many parallel beaded nerve fibres, derived from a large myelinated parent axon, lying between the muscle fibres of the fins. That they respond to stretch (as was inferred from their structure and position) was shown by Fessard & Sand (1937). Since these are the only sensory endings known in any fish which are stretch receptors lying amongst muscle fibres (neuromuscular spindles are absent from fishes), more information about their structure and relationships with the muscle fibres of the fins is desirable. In this note, we describe the ultra-structure of this simple type of stretch receptor, and the type of muscle fibre with which it is associated.