The present is an attempt to show the pattern of innervation, or neuronal geometry, of various nerves leading to their respective ganglia (Fig. 1) and to obtain visualization of the finest terminal branches. A description of the cellular arrangement of a segmental ganglion would be of value in better understanding the results obtained when using the axonal iontophoresis method applied to the third through seventh ventral nerve cord ganglia. A segmental ganglion of the thorax or abdomen is usually an oval mass of nerve tissue, continuous with the interganglionic connectives (Fig. A). Two or three principal lateral nerves extend from its sides. The ganglion is encased in a nucleated sheath, the neurilemma, which forms a continuous covering over the nerves and the connectives. The main cellular components of the ganglion, ganglion cells, are arranged peripherally, mostly in the lateral and dorsal parts. The central and ventral parts are occupied by a neuropil mass. The lateral nerves of the ganglion contain both motor and sensory fibers which arise from the dorsal and ventral roots, respectively, within the ganglion.