Page:Jardine Naturalist's library Entomology.djvu/181

Rh nerves in pairs, which visit all the principal organs, and ramify in all directions. The nervous system may be considered under two divisions, the ganglionic central cord, with its branches, and the nervous system of the esophagus and stomach. The former is the analogue of the spinal marrow, and the latter of the great sympathetic nerve. The ganglionic cord extends from the head to the hinder extremity, is situate beneath the intestinal canal, and runs along the ventral face of the body; (Pl. II. fig. 1, g, h, i, l, l.) This presents knotty expansions or ganglia at intervals throughout its whole course. Two of these are placed in the head, one above the esophagus near the pharynx, the other beneath it, and, considered collectively, they form what many authors have denominated the brain, (cerebrum and cerebellum of Burmeister.) The anterior of these cephalic ganglia, (the cerebrum,) lies transversely, and is usually more or less distinctly divided into two hemispheres. It emits a nerve to each of the antennæ, also the optic nerves, and lateral branches which unite it to the posterior cephalic ganglion. The optic nerves spring from the outer margin of each cerebral lobe, and are generally broad at the base and narrower at the extremity terminating in the eye. Their base is sometimes as wide as the lobes themselves, and in certain cases they are broader at the extremity than any part of the cranial ganglion. The optic nerves of the stemmata likewise originate from the same source, sometimes in single filaments, at other times divided near the extremity. After the