366 MOORE. [Vol. XIII. 



apical tubule loops always remain more or less prominent in 

 relation to the continuance of coeloraic excretion; while the 

 middle lobe, which alone is represented in the leeches, and 

 which is chiefly characterized by the fact that the efferent 

 tubule or its representative forms therein a complete circuit 

 instead of a simple loop, seems to develop in close relation to 

 the increasing nephridial blood supply. This is emphasized by 

 a study of the nephridia of the lower or water worms, in which 

 the blood supply is entirely wanting, or occasionally, perhaps 

 (Rhynchelmis) (34), very slightly developed. In these the mid- 

 dle lobe is lacking, and the nephridium consists of the simple 

 tubule loops, generally as in Lumbricus, two in number and 

 variously arranged. In many Tubificidae, Naidae, Lumbriculidae, 

 and Oelosomidae a single loop is developed; this may reach a 

 great length and be more or less folded on itself. 



The curious tufted nephridia of Pontoscolex (Urochaeta) (30) 

 and other forms are of a different type; but almost the entire 

 structure retains the characteristic narrow loops, which are, 

 however, much increased in number by repeated folding of the 

 tubule, and are arranged in close tufts. 



Using the presence of these simple excurrent and recurrent 

 loops as a test (and in the absence of details of more than a 

 few oligochaete nephridia this seems, in addition to the greater 

 functional activity of the funnel, to be the only one), we find on 

 comparing the discodrilid nephridium that it arranges itself at 

 once by the side of the oligochaete type, for the two apical 

 loops are very important and striking parts of the organ. The 

 most peculiar feature of the discodrilid nephridium is the large 

 size and complete integrity of the drain-pipe cells; they never 

 exhibit any indication of branching or splitting, but are always 

 essentially tubular cells perforated from end to end by a lumen 

 which never (certainly in B. illuminatus) forms lateral connec- 

 tions with the lumina of neighboring cells, even in the plexus 

 region. This, and especially the prominence of the apical loops, 

 places the discodrilid nearest to the tubificid type, as exhibited, 

 for example, by Iliodrilus (Stole, 32) or by Camptodrilus igneus 

 (Eisen, 19), but differing from these in the much greater devel- 

 opment of the plexus region, which further becomes doubled 



