PHYLUM NEMATHELMINTHES 



in 



th 



m< 



endodermal, this portion of the 

 canal being derived from the 

 archenteron of the embryo. 



Between the enteric canal and 

 the body-wall is a distinct space, 

 the coelome or body -cavity, con- 

 taining a clear fluid and more or 

 less encroached upon by the pro- 

 toplasmic processes of the muscle- 

 cells. The cavity is bounded ex- 

 ternally by these processes, in- 

 ternally by the outer cuticle of the 



testine : there is no trace of epi- 



elial lining such as occurs in 



ost of the higher animals. 



The excretory system presents 

 a certain resemblance to that of 

 Platodes. It consists of two longi- 

 tudinal canals (>,>'. v.\ one in each 

 lateral line. Anteriorly they pass 

 to the ventral surface, unite with 

 one another, and open by the 

 minute excretory pore (ex. p.) al- 

 ready noticed. 



The nervous system consists 

 of a ring (nv. r.) surrounding the 

 pharynx and giving off six nerves 

 forwards and six backwards (Fig. 

 226). Of the latter two are of 

 considerable size and run in the 

 dorsal and ventral lines respectively 

 (/////, lin.y. They are connected' with 

 one another by transverse commis- 

 sures (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 (im.) is thickened 

 and ganglion-like. The only sense- 

 organs are little elevations, the sen- 

 sorypapillce(Fig. 222,^.), on the lips. 



The reproductive organs are 

 formed on a peculiar and very 

 characteristic pattern. The testis 

 (Fig. 227, ts.) is a long coiled thread, 

 about the thickness of fine sewing- 

 cotton, and occupying a consider- 



279 



2 - 



