48 NATURAL SCIENCE. July, 



so many Annelids is usually the most typically metameric. Bourne 

 has, however, in his latest paper upon the earthworms of India, denied 

 the connection from segment to segment. The matter is, therefore, 

 still sub jitdice. From this diffuse and irregular network it has been 

 held that the two pairs of separate nephridia per segment have been 

 derived by reduction. Intermediate stages are offered by species with 

 two and three separate pairs. This view of the origin of the nephridial 

 system of the Oligochaeta has, however, received a series of shocks at 

 the hands of Vejdovsky (i6). Bourne (lo), and myself (3). We have 

 all shown beyond any doubt that in the genera Odockatus, Megascolides, 

 and Perichata, genera in which the excretory system of the adult is 

 constituted on the irregular, diffuse plan, the earliest appearance of 

 this system is in the shape of a series of paired tubes, one pair to each 

 segment. So far, therefore, Pevichceta has no right to be regarded as 

 a specially archaic form. It is, indeed, a matter of the greatest 

 difficulty to adjust the rival claims of the existing families. More 

 could doubtless be done if the exact relationships of the Oligochaeta to 

 other groups of "worms" could be definitely seen. In spite of the 

 immense accumulation of anatomical detail during the last few years, 

 but few facts which throw a light upon this most important question 

 have been laid hold of. Something has been done to remove the 

 barriers that were at one time supposed to divide the Oligochaeta from 

 the Leeches. The generally unpaired median male pores of the 

 Eudrilidae recall those of that group of Annelids; the continuity of the 

 oviduct with the ovary is another character that removes one difference 

 between the Leeches and the majority of the Eudrilidae ; finally, 

 the same family of earthworms shows a considerable subdivision of the 

 coelom by the formation of sacs enclosing the spermathecae and other 

 parts of the generative apparatus ; this is perhaps a foreshadowing of 

 the almost obliterated ccelom, to speak with no great exaggeration, 

 of the Leech. In two genera, viz., Megascolides and Deinodrilns, the 

 dorsal vessel is enclosed in a sac forming a sort of pericardium, which 

 is a step in the same direction. Even in histological details there 

 are resemblances now known to exist which were formerly regarded 

 as differences. Long ago Ratzel spoke of the leech-like muscular 

 fibres of certain Oligochaeta. The exact and beautiful researches of 

 Cerfontaine (13) have proved that, in the common earthworm — and 

 there is no doubt that the discovery applies to other Oligochaeta — the 

 muscular fibres consist of a softer granular core and of a radiately 

 striate denser sheath which appears to be the exact counterpart of the 

 muscular fibres of the Leech. This particular matter, however, takes 

 us rather further. Quite recently Hesse (14) has pointed out that in 

 the Enchytraeidae the muscles are more like those of a Nematode ; 

 he finds that, although there is apparently this ring of denser muscular 

 substance surrounding a granular core, a gap exists in the said ring ; 

 through this split, often hardly recognisable owing to its fineness, the 

 granular substance protrudes and is continuous with a large nucleated 



