THE NEPHRIDIA OF THE POLTCHJITA. 785 



It will be seen at once^ however, that the adoption of such 

 a view as this would lead us into a maze of difficulties, from 

 which there appears to be no escape, if our theories concern- 

 ing the Polychsete nephridium are to be at all consistent with 

 well-established conclusions concerning the structure of allied 

 groups.! Take the case of the Phyllodocids, for instance. 

 It would have to be supposed that in these worms the ori- 

 ginal funnel became separated off, that the truncated ne- 

 phridial canal acquired a highly complex, closed, branching 

 extremity, and that the funnel became again grafted on at 

 maturity to reassume something of its original relations and 

 function. For all this there is, of course, not a scrap of 

 evidence. Moreover, it is directly opposed to such evidence 

 as we have from the study of development, that the further 

 we go back, the earlier the stage investigated, the less close 

 is the connection between the nephridium and the genital 

 funnel (Part II, p. 454, Part III, p. 702). 



Far more natural is it to compare the closed, generally 

 branched, nephridia of Phyllodoce, Nephthys, and Glycera, 

 with the branched organs ending in flame-cells found in the 

 Platyhelminths, Rotifers, and Nemertines (see p. 738 below). 

 The solenocytes, indeed, appear to be comparable only to 

 flame-cells. Such, at all events, must be the conclusion 

 until a knowledge of their development warrants another 

 opinion. 



This view is further supported by the knowledge that 

 many nephridia, which in the adult condition open into the 

 coelom, pass through a " protouephridial " stage with closed 



funnel, and acting as a genital duct. Now this is just what is not the case in 

 Polygordius. Here the genital products escape by rupture of the body-wall, 

 and the nephridia have only small nephrostonies (p. 715). 



Moreover, there really appears to be nothing in what we know of the 

 structure of these worms which warrants any other view but that they are 

 a specialised offshoot from the Polychsete stem. And it may be pointed out 

 that some of those very authors who would consider them as primitive 

 Archiannelids, associate them wrecklessly with forms like Dinophilus and 

 Saccocirrus, where the genital ducts acquire an unusual complexity. 



1 See also p. 730, and my general paper (10). 



