Major nerves in the anterior nervous system of Macracanthorhynchus hirudinaceus (Acanthocephala)

Abstract

1. 1. The anatomy of the cephalic ganglion and associated nerves in the Acanthocephalan Macracanthorhynchus hirudinaceus has been studied preliminary to use of the organ as a model system for the study of neural pathways. 2. 2. Analysis of routine serial sections of the anterior portion of the worm revealed the existence of eighty-six cells within the cephalic ganglion itself. 3. 3. There are six pairs of nerves with bilateral symmetry which exit from the ganglion. The total number of neurons contained within the six pairs of nerves is approximately seventy-two. 4. 4. This investigation reveals that certain anatomical features are either new or different from that which has been proposed by earlier workers. Among these observations are the following: (a) The anterior ventral nerve does not branch but is always two separate bundles of neurons. (b) The anterior ventral nerve is not wrapped in muscle as is the lateral posterior nerve after it leaves the thick layer of the dorsal receptacle. (c) The paired lateral posterior nerve consists of two bundles of neurons with approximately twenty-three neurons/bundle. (d) The lateral posterior nerve originates exclusively from the dorsal concave surface of the brain and never from the convex or ventral surface.