IV 



VERMESNER VO US SYSTEM 



227 







tudiiial 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 



Be- 



to be wanting. 



FIG. lol. Head of Sagitta bipunct- 

 ata, seen from above, with closed 

 seizing hooks, after O. Hertwig. g, 

 LnSetOg'natiia, Brain; gh, seizing hooks ; sc, commissure 

 ~ r S. 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 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-cesophageal 



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-cesophageal 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 hexapteraT" seen"" from 



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



after running through the ventral ganglion, are - Hertwi s- .Mouth;d 



o t> & ' intestine ; sc, cesophageal 



round as 2 strong longitudinal strands, which, 



Fn;. I.JL'. Sagitta 



after giving off numerous lateral nerves, them- 

 selves end in fine nerve fibres. All nerves diver- 



commissure ; fy, ventral 

 ganglion ; fl, fins ; or, 

 (ivarium ; ovd, oviducts ; 

 tco, female genital apc-r- 



ing from the ventral ganglion and the posterior tare ; , anus ; iw, testes ; 

 longitudinal nerves pass finally into a plexus of * ^cavity; sz, sperm 



v . n -. 1 i -L i i i (luct : sb > sperm vesicle; 



gangliomc cells and nerve fibres, which is developed ^ caudal iin 



