IV 



VERMES— NERVOUS SYSTEM 



227 



r/h 



tudinal nerves rise out of it, which pass by the mouth, and run on both 

 sides of the body 

 immediately be- 

 neath the integu- 

 ment to its pos- 

 terior end. These 

 longitudinal nerves 

 must represent the 

 separated lateral 

 halves of the ven- 

 tral chord of the 

 Annulata. Trans- 

 verse commissures 



seem to be wanting. 



Fig. IGl. — Head of Sagitta bipunct- 

 ata, seen from above, with closed 

 seizing hooks, after 0. Hartwlg. g, 

 vnSetOg'nB.tllR Brain ; (/?t, seizing hooks ; sc, commissure 

 {Figs. 151 and 152). between brain and ventral ganglion ; a?i, 



rr\,a nprvniio °P*'° "^''^^ ' ™' '^^'^ ' ™' ^"t™or portion 



iiiB lieivoua of the olfactory organ;™, olfactory nerve. 



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 trunk segment and surpasses the 

 cephalic ganglion in size. The cephalic and ventral 

 ganglia are connected by 2 long commissures. 

 Besides these 2 commissures, the supra-oesophageal 

 ganglion gives off 2 strong nerves which penetrate 

 the mesoderm forwards and downwards, and which 

 we may call motor nerves, 2 lateral nerves which 

 supply the integument of the head, 2 outer pos- 

 terior nerves which, after a short course, reach 

 the 2 eyes behind the supra-oesophageal ganglion 

 (nervi optici), and 2 inner posterior nerves which 

 supply the unpaired sensory organ lying behind 

 the eyes which is supposed to be the olfactory 

 organ (nervi olfactorii). A great number of nerves 

 radiate from the ventral ganglion, among which hexapterai 

 the continuations of the 2 oesophageal commissures, 

 after running through the ventral ganglion, are 

 found as 2 strong longitudinal strands, which, 

 after giving off numerous lateral nerves, them- 

 selves end in fine nerve fibres. All nerves diverg- 

 ing from the ventral ganglion and the posterior 

 longitudinal nerves pass finally into a plexus of 

 ganglionic cells and nerve fibres, which is developed 



Fig. 



152. — Sagitta 

 seen from 

 the ventral side, after 

 0. Hertwig. m. Mouth ; d, 

 intestine ; sc, (Esophageal 

 commissure ; &(/, ventral 

 ganglion ; jl^ fins ; ov, 

 ovarium ; ovd, oviducts ; 

 wo, female genital aper- 

 ture ; a, anus ; Uo, testes ; 

 sh, tail cavity; si, sperm 

 duct ; sh, sperm vesicle ; 

 sjl, caudal fin. 



