296 



ZOOLOGY 



SECT. 









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The excretory system con- 

 sists of two longitudinal canals 

 (ex. v.), one in each lateral line. 

 Anteriorly these pass to the ventral 

 surface, unite with one another, and 

 open by the minute excretory pore 

 (ex. p.) already noticed. The 

 system is not ciliated, contains no 

 flame-cells, and has no internal 

 openings. Each canal is an ex- 

 cavation in a single enormously 

 elongated cell with a single nucleus. 



The nervous system consists 

 of a ring (nv. r.) surrounding the 

 pharynx and giving off six nerves 

 forwards and six backwards (Fig. 

 246). Of the latter two are of 

 considerable size, and run in the 

 dorsal and ventral lines respectively' 

 (dln.,vln.). They are connected with 

 one another by transverse com- 

 missures (c.), and the ventral nerve 

 swells into a ganglion just in 

 front of the anus. The pharyngeal 

 nerve-ring contains nerve-cells, and 

 its ventral portion (un.) is thickened 

 and ganglion-like. The only sense- 

 organs are little elevations, the 

 sensory papillce (Fig. 242, p.), on 

 the lips. 



The reproductive organs are 

 formed on a peculiar and very 

 characteristic pattern. The testis 

 (Fig. 247, ts.) is a long, coiled 

 thread, about the thickness of fine 

 sewing-cotton, and occupying a 

 considerable portion of the body- 

 cavity. At its posterior end it is 

 continuous with the vas deferens, 

 the two passing insensibly into one 

 another so that the junction is 

 not visible externally. The vas 

 deferens, in its turn, becomes con- 

 tinuous with a wide canal, the 

 vesicula seminalis\(vs. sem.) which 

 opens by a short, narrow muscular 

 tube, the ductus ejaculatorius, into 



