Endocrine activity in the crustacean nervous system

Abstract

A search for evidence of secretion was made in the tritocerebral commissure region of species belonging to the families Penaeidae and Palaemonidae, using several histological techniques and injection experiments. Two fine nerves leave the tritocerebral commissure in the crustaceans examined and supply paired muscles nearby. A great many acidophil droplets lie along the course of these nerves. In Penaeus braziliensis at the point where each post-commissure nerve reaches the muscle which it innervates there is an enlargement of the epineurium which forms a flat plate, filled with acidophil droplets; this is partially fused to the wall of a blood-sinus. This 'sinus-plate' seems in many respects to be analogous to the sinus-gland of the eye-stalk. In the members of the Palaemonidae examined no discrete sinus-plate was seen, but the post-commissure nerves were wide and flat for the proximal part of their course; many acidophil droplets lay in the flat portion of the post-commissure nerves and in the epineurium of the commissure nearby. The regular arrangement of these droplets in Leander serratus suggests the possibility that they may travel along branched pathways in the epineurium. Large cells suspected to be secretory were found within the commissure, close to its hinder margin near the points of emergence of the post-commissure nerves, and in the connective ganglia. Fibres from these latter cells pass along the post-commissure nerves. Injection experiments showed that those regions richest in acidophil droplets yielded extracts with a powerful effect on dispersed white and red pigments in chromatophores. It is suggested that two hormones, probably produced by neurosecretory cells in the tritocerebral commissure and in the connective ganglia, are stored and released by specialized portions of the epineurium of the post-commissure nerves and of the commissure.