ANATOMY OF THE CENTRAL NERVOUS SYSTEM OF ARMADILLIDIUM VULGARE (LATREILLE) (ISOPODA)

In an anatomical investigation of the central nervous system of the terrestrial isopod Armadillidium vulgare (Latreille), some specimens were dissected; others were sectioned and stained for light microscopical study. The brain, consisting of protocerebral, deutocerebral, and tritocerebral divisions, is situated ventrally in the extreme anterior region of the cephalothorax. The protocerebrum is bilobed and divided dorsally by a deep, median cleft. Each lobe (=optic lobe) tapers to form a large optic nerve. A pseudofrontal organ is suspended ventrally from the distal extremity of each optic lobe. A pair of accessory lobes extends ventrally beneath the main lobes of the protocerebrum. The deutocerebrum is much reduced in size, reflecting an apparent adaptive trend among terrestrial isopods (and amphipods) toward reduction of the antennules and associated loss of olfactory function. The well-developed lobes of the tritocerebrum extend laterally and continue as the circumesophageal connectives, completing encirclement of the esophagus to form a paired connective that unites with the subesophageal mass. The subesophageal mass is a fusion of the mandibular, maxillulary, maxillary, and maxillipedal ganglia. The ventral nerve cord, for most of its length, consists of seven pereionic ganglia joined by paired longitudinal connectives and smaller, single, median intermediate connectives. Six pairs of pleonic ganglia are fused into a single pleonic mass. Characteristic groupings of nerve cell bodies occur on the surfaces of the brain and ventral nerve cord. Distinctive, small, and densely packed glomerular cells occupy the surfaces of the optic lobes. Neuropiles and fiber tracts form conducting pathways, although those of the ventral cord are not so distinct morphologically as are some in the brain. Strong tagmatization is suggested by fusion to form a single pleonic mass.