Giant Neurons and Axon Pathways in the Brain of Tritonia

Much of the recent work on the giant cells in the central nervous system of gastropods is related to the activity and the electrical properties of individual cells (Tauc, 1955, 1957, i960, 1962; Arvanitaki & Chalazonitis, 1956; Kerkut & Walker, 1961). Although this has greatly advanced our understanding of the physiology and pharmacology of the individual neurons, there is still much to be learned of the nature and organization of the integrative pathways between the ganglia and the topography of the brain in relation to the behaviour of the animal. Some progress towards this end was made by the earlier workers using techniques of lesion and stimulation of the nerves combined with recording the electrical and mechanical responses, particularly from the foot (Herter, 1931; Postma, 1943). More recently, transmission across molluscan ganglia has been studied by Turner & Nevius (1951), Horridge (1961) and Nisbet (1961). Although this work has yielded some information of a general nature on the pathways through the brain, it is complicated by the large number of units involved and gives no clear picture of the events taking place inside the ganglia. Hughes & Tauc (1962, 1963) have combined stimulation techniques with intracellular recording from ganglion cells to study the branching axons of the giant cells and cells from the pleural ganglion of Aplysia. As yet, these investigations have not provided the answer to the question of their function. The brain of Tritonia seems to offer some advantages over Aplysia for studies of this nature, with its more generous allocation of giant cells and the compact nature of the ganglia. The present paper describes some of these features and the distribution of axons from some of the giant cells to nerves on both sides of the brain.