The Neurosecretory System of the Vena Cava In Cephalopoda I. Eledone Cirrosa

Abstract

Nerves known to supply the anterior part of the vena cava in Cephalopoda have been found to belong to a special system for which the term ‘neurosecretory system of the vena cava’ (NSV system for short) is proposed. In Eledone cirrosa this system consists of neurons whose cell bodies are aggregated: (a) in the visceral lobe in a layer termed the NSV layer; (b) in the ganglionic trunks continuous with this layer and associated with nerves arising from the visceral lobe—there is on each side a ‘lateral NSV trunk’ accompanying the nervus infundibuli posterior, and a ‘medial NSV trunk’ accompanying the nervus visceralis. Each of these trunks in its further course separates from its nerve and runs far in the caudal direction diminishing in thickness and giving off sideshoots of irregular shape which end blindly in the loose connective tissue and show no connexions with any organ.The NSV layer and trunks consist of unipolar nerve cells of small size and uniform appearance. Their very thin axons unite in bundles which form nerves running to the vena cava. The total number of neurons of the NSV system, approximately estimated, must be over two millions. The disposition of the elements of this system is peculiar in that the axons of the cells situated in the caudal prolongations of the ganglionic trunks must run far rostralwards until they reach the nerves to which they contribute.The nerves entering the vein penetrate through its muscle coat and form a network under the endothelial lining of the vein; this continuous neuropile layer extends from the anterior end of the vein to the entrance of the vena hepatica; all this part of the vein has on its inside longitudinal ridges formed by the uneven thickness of the neuropile layer.