108 



P. HATAI. 



Nephrìdium. 



The nephridia are present in segments VII — IX and in all segments 

 posterior to XII inclusive except the last. In each nephridium we may dis- 

 tinguish three portions, the internal tubular portion, the middle enlarged portion, 

 and the external tubular portion. The middle portion makes up by far the 

 larger part of the whole organ, and reaches nearly the posterior septum of the 

 segment on either side of the intestine ; externally it is continuous with its fellow 



on the opposite side of the body, al- 

 though the nepbridial canals of the 

 two are entirely separate. The ex- 

 ternal tubular portion opens to the 

 exterior on the outer side of the ven- 

 tral seta-bundle. The funnel is very 

 small, and is somewhat sagitate or 

 globular according as the ciliated 

 process is thrown out or drawn in ; 

 the latter being formed by the ventral 

 margin of the funnel. (In V.pilosus 

 it is formed by the dorsal lip of the 

 funnel.) The internal surface of the 

 funnel as well as its margin is thickly 

 covered with long vibrating cilia, and 

 during life the ciliated process is con- 

 tanti)- thrown out and drawn in. 

 Sections show that there is a trans- 

 verse constriction at its base, upon 

 which it is folded when drawn in. 



There is only one nepbridial 

 canal of small [calibre, which winds 

 back and forth several times in the 

 enlarged middle portion. The por- 

 tion lying between the nephridiopore 

 and the middle jxtrtion , sends out 

 several blind diverticula. The walls 

 of the canal consist mostly of a syn- 



Cut 4. 



C.cxt. C;mal to the exterior, re. Nepbridial 

 canal, n.f. Nr phridiostome, n p. Nephridiopore. 



