34 



OLIGOCHAETA 



Fig- 5- 



limited to one side of the body ; with these exceptions all the aquatic Oligochaeta 

 possess paired nephridia a pair to each segment ; in all of these families, however, 

 the nephridia are missing from a certain number of segments at the anterior end 

 of the body. This state of affairs, however, is by no means confined to the Microdrili. 

 It is met with in Pontodrilus, and the genera Glyphidrilus, Annadrilus, and 

 Sparganophilus among the Geoscolicids ; the actual segment in which the nephridia 

 commence is a matter which varies ; and as it is rather of classificatory interest, 

 I refer to the description of species for more exact data. In the aquatic Oligochaeta 

 even if, as in the Lumbriculidae, the nephridia commence before the genital segments, 

 those segments never contain nephridia ; in earthworms, on the other hand, nephridia 

 are present in the genital segments, except in certain of the genital segments in the 

 few species mentioned above as resembling the aquatic families in the want of 

 nephridia in the anterior segments of the body. The nephridia are always much 

 coiled tubes ; and they always occupy two segments and two segments only 1 . The 



internal aperture, the funnel, lies a segment in front of 

 that which bears the external pore. In the lower Oligo- 

 chaeta the nephridia have no blood supply 2 ; they are always 

 covered by a layer of peritoneum, the cells of which are 

 often very large. 



The nephridium of Psammoryctes barbatus will be 

 selected as an example of a nephridium in one of the lower 

 Oligochaeta ; it is fully described and figured by VEJDOVSKY 

 (24, PI. ix, fig. i). The funnel which is composed of but few 

 cells passes into a delicate spirally-wound tube decked with 

 large clear vesicular peritoneal cells ; this passes into a thicker 

 walled section of a yellowish colour ; this again passes into 

 a clear walled tube which ends in a somewhat voluminous 

 contractile bladder opening on to the exterior. In other 

 NEPHKIDIUM OF MARioNiA aquatic forms the nephridia may be simpler ; but the same 

 SPHAGNETORUM. regions are generally recognisable ; not, however, in the 



(After Michaeken.) Enchytraeidae whose nephridia (fig. 5) are very peculiar and 



resemble in many particulars the young developing nephridia of the higher Oligochaeta. 

 A solid cellular mass, varying in shape according to the genus, is traversed by a coiled 

 tube, the coiling of which again differs in different forms ; from this arises a duct 



1 Doubtfully excepting Plutellns. See also remarks on nephridia of Aeolosoma. 



1 Rhynchdmis is an exception (possibly other Lumbriculidae also) ; VEJDOVSKY has figured (9, PI. xxvi, fig. 20) 

 a bloodvessel following the coils of the nephridium. 



