IV 



VERMES NERVOUS SYSTEM 



227 



m. 



ovd 



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 ' //j^. \{ 

 Annulata. Trans- L>- v ' J^.,jLkl 



verse commissures FIG. 151. Head of Sagitta bipunct- 



.bewanting. ata > seen from above ' wiih closed 



seizing hooks, after O. Hertwig. g, 



Cil36tOg > na,tn3, Brain ; gh, seizing hooks ; sc, commissure 



3. 1 5 1 andl 52). between brain and ventral ganglion ; an, 



rp-i optic nerve ; au, eye ; ro, anterior portion 



8 of the olfactory organ ; rn, 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 

 the continuations of the 2 oesophageal commissures, the ventral side, after 

 after running through the ventral ganglion, are - He J twi s- m > Mouth ;*> 



,. , , . ' intestine ; sc, oesophageal 



tound as. 2 strong longitudinal strands, which, commissure; ig, ventral 



after giving off numerous lateral nerves, them- ganglion; fl, fins; o, 



selves end in fine nerve fibres. All nerves diverg- ^^^\Q^^^ 



ing from the ventral ganglion and the posterior tore ; a, anus ; ho, testes ; 



longitudinal nerves pass finally into a plexus of sh ' tail cavit y ; sl > s P erm 



! ,-, , , -i -i i T T duct: sb. snfirm vpsiplp 



gangliomc cells and nerve fibres, which is developed 



d 



* 



