In the succeeding ganglia the lobes are in general motor; the fibres composing the œsophageal commissures, and which arise from the œsophageal commissural lobes, extend not only to the subœsophageal ganglion, but pass along through the succeeding ganglia to the last pair of abdominal nerve-centres.[40] Since, then, there is a direct continuity in the fibres forming the two main longitudinal commissures of the nervous cord, and which originate in the brain, it seems to follow that the movements of the body are in large part directed or coördinated by the brain.[41] Still, however, a second brain, so to speak, is found in the third thoracic ganglion of the locust, which receives the auditory nerves from the ears situated in the base of the abdomen; or in the first thoracic ganglion of the green grasshoppers (katydids, etc.), whose ears are situated in their fore legs; while even the last pair of abdominal ganglia in the cockroach and mole cricket, is, so to speak, a secondary brain, since it distributes sensory nerves to the caudal stylets, which are provided with organs probably olfactory in nature. It is impossible to understand the morphology of the brain unless we examine the mode of origin of the nervous system in the early life of the embryo. The head of an embryo insect consists of six segments, _i.e._ the ocular, antennal, premandibular, mandibular, and the 1st and 2d maxillary segments, so named from the appendages they bear. Of these the first three in the larva and adult are preoral, and the last three are postoral. The antennal segment was probably either postoral in the progenitors of insects, or the antennæ were inserted on the side of the mouth, the latter finally moving back.[42] The nervous system in the early embryonic condition, as shown by Wheeler (Fig. 245), at first consists of nineteen pairs of primitive ganglia, called _neuromeres_. Those of the head, which later in embryonic life fuse together to form the brain, are the first three, corresponding to the _protocerebrum_, _deutocerebrum_, and _tritocerebrum_ of Viallanes. The first pair of primitive ganglia, and which is situated in front of the mouth, is divided into three lobes. [Illustration: FIG. 245, _A-D_.—Diagrams of four consecutive stages in the development of the brain and nerve-chain of the embryo of Xiphidium: I, cephalic,—II, thoracic,—III, abdominal, region; _st_, stomodæum or primitive mouth; _an_, anus; _e_, optic plate; _pc(og)_, 1st protocerebral lobe, or optic ganglion; _pc^2_, _pc^3_, 2d and 3d protocerebral lobes; _dc_, deutocerebrum; _tc_, tritocerebrum; 1–16, the 16 postoral ganglia; _po. c_, postoral commissure; _fp_, furcal pit; _ac_, anterior,—_pc_, posterior, ganglionic commissure; _ag_, anterior,—_pg_, posterior,—_cg_, central,—_lg_, lateral gangliomeres.—After Wheeler. ]