. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 610 NERVOUS SYSTEM. (COMPARATIVE ANATOMY.) each other by sensitive columns. A tract has also been recently described by Mr. Newport,* passing along the dorsal surface of these co- lumns, and giving off lateral nervous branches ; this has been regarded as a molar tract. Mi- nute anatomy has also unfolded to us what may be considered as the analogue of the re- spiratory system of nerves, and a par vagum. These points we will now notice in detail, commencing with the Hemipterous Insecta, in which the nervous system is least
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 610 NERVOUS SYSTEM. (COMPARATIVE ANATOMY.) each other by sensitive columns. A tract has also been recently described by Mr. Newport,* passing along the dorsal surface of these co- lumns, and giving off lateral nervous branches ; this has been regarded as a molar tract. Mi- nute anatomy has also unfolded to us what may be considered as the analogue of the re- spiratory system of nerves, and a par vagum. These points we will now notice in detail, commencing with the Hemipterous Insecta, in which the nervous system is least perfectly or- ganized. In the perfect state of the Ranatra Itneuris the nervous system consists (besides the supra-cesophageal nervous accumulation) of a small round ganglion (Jig. 345, a), situated below the oesophagus at its very commence- Fig. 345. Ven'ral nervous cord of Ranatra linearis (perfect state), magnified to about twice the natural size. n, small round sub-cesophageal ganglion, b, large quadrilobate thoracic ganglion, c, c, fila- ments passing down the lengthened abdomen. rnent; from this two longitudinal commissures pass to join with a large quadrilobate ganglion (/>), situated at the further extremity of the thorax. From each side of this ganglion there are given off three nervous threads, passing superiorly, transversely, and inferiorly; and from the lower part of the ganglion, which is slightly fusiform in shape, there are given off two bundlesof most minute and delicate nervous fila- ments (re), each containing five branches, which pass downwards into the lengthened abdomen to supply the parts situated in that region; there is also a supra-cesophageal nervous accumulation. In the Orthoptera the nervous system presents a certain degree of concentration worthy of no- tice. In the perfect state of a species of Acrydium there are two comparatively large thoracic ganglia, very near each other, and connected, as usual, by commissures; in the abdomen there are f
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