318 W. BLAXLAND BENHAM. 



contented themselves with a brief mention of the fact of its 

 presence^ or given only a rough sketch of it. It appears to me 

 that, just as the character of the nephridium itself in various 

 genera is of interest and importance as representing to some 

 extent probable stages in the phylogeny of the organ^ so the 

 nephrostome will indicate such steps. 



Amongst the leeches, we know from Bourne's researches that 

 Clepsine has a funnel composed of only two cells (14, fig. 52) ; 

 other leeches show an increase in number of these cells ; and 

 Hirudo, with its more complicated nephridium, possesses a 

 very large number of funnel-cells, each perforated or partially 

 perforated by a branch of the nephridial tubule. 



Amongst the Microdrili^ such as Tubifex and Enchy- 

 trseus, two is the normal number of cells composing the 

 funnel. In Hhynchelmis there are eight such cells. In 

 the plectonephric earthworms, such as Acanthodrilus, and 

 the smaller tubules ofMegascolides no funnels are present. 

 In Perichseta from eight to fifteen marginal cells form the 

 funnel; in the large tubules of Megascolides a larger 

 number of cells are present, which from Spencer's drawing 

 (30, pi. vij fig. 26) appear to be arranged in a complete 

 circle round the aperture, as in P. malamaniensis. In 

 the higher meganephric condition we come across larger 

 funnels, as a rule, with a great number of marginal cells, 

 which form an incomplete circle, and difi'er in size according 

 to their position.^ 



In my figure illustrating this anatomical point of Uro- 

 benus (9, pi. viii, fig. 19) I have drawn a number of cells 

 curving inwards from the ends of the marginal cells, which 

 are arranged in a horseshoe. These cells are no doubt the 

 ''centripetal marginals^' and "centrifugal gutter-cells" of 

 Lumbricus, although when I made the drawing I had a very 

 imperfect idea as to their meaning. For Urochseta, Perrier 

 (26, pi. xvi, fig. 42) gives a large drawing of the funnel, which 

 presents a very wide aperture to the coelom ; the margin of 



' An exception is to be noted in the case of Microchseta rappi, where 

 the funnel seems peculiar, and may perhaps be degenerate. 



