STRUCTURE OF THE NEPHRIDIA OF DTNOPHILUS. 541 



further complicated by their hermaphroditic condition, I 

 think it would be as just to assume that in them the vesiculi 

 and vasa differentia also represent modified portions of the 

 nephridial system. In the Turbellaria either the male or the 

 female sexual organs are readily reducible to the conditions 

 presented in Dinophilus. This, connected with the changes 

 necessary in the position of the relative parts of the nephri- 

 dium in order to make it agree with the observed growth of 

 the vesicles in young worms as described by Harmer (8) 

 renders it probable that they are not modified nephi-idia. It 

 is true, as Montgomery (18) has pointed out, no hard or fast 

 distinction can be drawn between the blastocoel and coclom 

 as morphologically distinct spaces ; since their presence as 

 separate cavities is dependent to a large extent on the form 

 of cleavage and gastrulation, which often differs so greatly 

 in closely allied forms. While realising no great import- 

 ance can be attached to the separation of these spaces, 

 nevertheless in Dinophilus this separation is so well 

 marked that it is hard to suppose that the nephridia of the 

 fifth segment could readily lose their connection with one 

 space, and acquire openings into that of the oilier in the 

 manner Harmer supposes without showing more obvious 

 evidence of this change. This view will certainly need more 

 conclusive evidence in its favour than has so far been ad- 

 vanced for it, and it is possible ultimately it will prove to be 

 wrong. 



VII. Summary. 



In the present paper it has been shown that the nephridia 

 of Dinophilus are of the primitive solenocyte-bearing type 

 so frequently found in Annelids. In the male there are four 

 such pairs of nephridia whose solenocytes project into the 

 primary body-cavity or blastocoelic space about the gut. 

 The shape and general position of the nephridia is the same 

 as Harmer (8) has already described for this species. The 

 terminal portion of the nephridial ducts, however, probably 



