Neurosecretion and salt and water balance in the Annelida and Crustacea.

SYNOPSIS. The possible role of .the neurosecretory system in regulation of salt and water has been studied in the annelids and crustaceans. In the earthworm, Lumbricus terrestris, a brain factor influences 'the salt and osmotic concentration of the blood and coelomic fluid. Removal of the brain results in the increase of water influx with a decrease in the salt and osmotic concentrations of the body fluids. The decreases in salt and osmotic concentrations can be prevented by the implantation of the brain or the injection of brain homogenates. In the freshwater crayfish, Procambarus clarkii, a factor, presumably secreted in the brain and released in the eyestalk, seems to maintain the normal permeability of the body surfaces to water. Eyestalk removal, which eliminates the release site, results in the increased influx of water with a decrease in the salt concentration of the blood. A brain factor also seems to be involved in maintaining the sodium and osmotic concentrations of the blood. In the semi-terrestrial grapsid crab, Metopograpsus messor, the thoracic ganglion, under the control of an eyestalk element, secretes a factorinvolved in increasing the permeability of the body surfaces to water. The removal of the eyestalks, the implantation of the thoracic ganglion, or the injection of extracts of thoracic ganglia, results in changes in the osmotic concentration of the blood tending toward that of the medium. In all three species studied, the neuroendocrine factors seem to be involved primarily in the regulation of the permeability of the body surfaces to water.