FIG. 248.—1, front view of the brain of _Melanoplus femur-rubrum_: _opt. gang_, optic ganglion; _oc_, ocelli and nerves leading to them from the two hemispheres, each ocellar nerve arising from the region containing the calices; _m. oc_, median ocellar nerve; _opt. l_, optic lobe sending off the optic nerve to the optic ganglion; _ant. l_, antennal or olfactory lobe; _ant. n_, antennal nerve; _f. g_, frontal ganglion of sympathetic nerve; _lbr. n_, nerve to labrum; _x_, cross-nerve or commissure between the two hemispheres; _œ. c_, œsophageal commissure to subœsophageal ganglion. 2, side view of the brain and subœsophageal ganglion (lettering of brain as in 1): _s. g_, stomatogastric or sympathetic nerve; _a. s. g_, anterior, and _p. s. g_, posterior, sympathetic ganglia; _g^2_, subœsophageal ganglion; _md_, nerve to mandible; _mx_, maxillary nerve; _ln_, labial nerve; _nl_, unknown nerve,—perhaps salivary. 3, interior view of the right half of the head, showing the brain in its natural position: _an_, antenna; _cl_, clypeus; _lbr_, labrum; _m_, mouth-cavity; _md_, mandible; _t_, tongue; _œ_, œsophagus; _c_, crop; _en_, right half of the endocranium or =X=-shaped bone, through the anterior angle of which the œsophagus passes, while the great mandibular muscles play in the lateral angles. The moon-shaped edge is that made by the knife passing through the centre of the =X=. 4, view of brain from above (letters as before). 5, subœsophageal ganglion from above: _t. c_, commissure to the succeeding thoracic ganglion (other letters as before). Fig. 3 is enlarged 8 times; all the rest 25 times.—Drawn from original dissections, by Mr. Edward Burgess, for the Second Report of the U. S. Entomological Commission. ] The pair of subœsophageal ganglia distributes nerves to the mandibles, to the 1st and 2d maxillæ, and to the salivary glands (Fig. 248). Its general shape and relations to the walls and to the outer organs of the head is seen in Figs. 247, 248. In all the winged insects (Pterygota) its plane is situated more or less at right angles to the horizontal plane of the ventral cord. On the dorsal and anterior sides are situated the ocular lobes, and below these the antennal lobes. Viallanes first, independently of embryonic data, divided the brain of adult insects into three regions or segments; _i.e._ the “_protocerebron_,” “_deutocerebron_” and “_tritocerebron_,” which he afterwards found to correspond with the three primitive elements (neuromeres) of the brain and with the segments of the head of the embryo. The brain of the locusts (Melanoplus and Œdipoda) being best known will serve as the basis of the following description, taken mainly from Viallanes, with minor changes in the name of the three segments, and other modifications.