Text-book of comparative anatomy . ; nt, nephridialfunnel; gf, genital folds ; ov, ovaries ; dm, dorsal mesentery ; rm, ven-tral mesentery. ing a plexus. The nervous system of the Brachiopoda lies under theintegument. In the Bryosoa, only the supra-resophageal ganglion of the cesoph-ageal ring is retained; it lies as a generally inconsiderable mass (occa-sionally with thickened lateral parts) dorsally over the fore-gut, betweenmouth and anus, under the integument. From this ganglion nervesrun chiefly into the tentacles, and further to the two ciliated pits,when such are present. Rotatoria.—Ove
Text-book of comparative anatomy . ; nt, nephridialfunnel; gf, genital folds ; ov, ovaries ; dm, dorsal mesentery ; rm, ven-tral mesentery. ing a plexus. The nervous system of the Brachiopoda lies under theintegument. In the Bryosoa, only the supra-resophageal ganglion of the cesoph-ageal ring is retained; it lies as a generally inconsiderable mass (occa-sionally with thickened lateral parts) dorsally over the fore-gut, betweenmouth and anus, under the integument. From this ganglion nervesrun chiefly into the tentacles, and further to the two ciliated pits,when such are present. Rotatoria.—Over the oesophagus there lies a ganglion (supra-oesoph-ageal ganglion) which sends off nerves to the wheel organ, the cutaneousorgans of touch, and the muscles. It lies under the integument. In Duiopliilus also, in front of and above the mouth (in the pro-stomium), is found a mass of fibres surrounded by ganglionic cells, whichrepresents the supra-resophageal ganglion. In Dinophilus gigas two longi- IV VERMES—NERVOUS SYSTEM 227. tudiiial nerves rise out of it, which pass by the mouth, and run on bothsides of the bodyimmediately be-neath the integu-ment to its pos-terior end. Theselongitudinal nervesmust represent theseparated lateralhalves of the ven-tral chord of theAnnulata. Trans-verse commissures Be- to be wanting. FIG. lol.—Head of Sagitta bipunct-ata, seen from above, with closedseizing hooks, after O. Hertwig. g,LnSetOgnatiia, Brain; gh, seizing hooks ; sc, commissure~rS. 151 aild!52). Between brain and ventral ganglion ; an,_£i , optic nerve ; au, eye ; ro, anterior portion of the olfactory organ ; rn, olfactory nerve. ovtL- .• la I A: $ —ovd —d nro system is here well developed. The central nervous system and the peripheral nerves lie, with the exception of a single portion, external to the musculature in the body epithelium. The brain or supra- oesophageal ganglion lies dorsally in the head segment, while the infra-cesophageal ganglion lies ventrally in the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
