Austrdlian Earthivonns. 235 



Microscopic Structure. — Transverse serial sections of this 

 form show the funnel to be A-ery small, and, unlike the nephri- 

 diopores, constant in position, being situated between the first 

 and second setae from the midventral line on each side. [cf. 

 Benliam, (4)]. The general arrangement shown in the figure 

 (20) is reconstructed from a series of sections. As can be seen, 

 the same parts are present in both nephridia, the coils differing 

 in length, according as the vesicle opens dorsally [Fig. 20, O.N.B.] 

 or ventrally [O.N. A.]. Tlie histology of one of my series was par- 

 ticularly go«d, so that the structure of the various parts could 

 be worked fairly completely. The funnel in very small, formed 

 by a few marginal cells, columnar in shape, and ciliated. The 

 tube leading from this divides into two parts, the thinner one 

 of which passes at once to the vesicle, being shorter in nephri- 

 dium A than in B ; while the thicker one in both nephridia 

 coils in (letiiiite ways and ends blindly. In section, the tube 

 leading from the funnel is seen to contain an intracellular duct 

 which, at the point X passes into the coiled tube c.n. [Fig. 20], 

 It continues as a straight lumen as far as the blind end [Fig. 

 20, Y.], where a section shows clearly that the lumen turns back 

 on itself, and becoming somewhat wider, coils slightly in the 

 thickness of the tube until it reaches point X again, where the 

 duct passes as a single straight limien to open into the vesicle 

 [o.v.]. This arrangement is strictly comparable with that of 

 the nephridium of Lumbricus described by Benham (3), the 

 intracellular straight lumen being Benham's '' narrow tube,'' 

 while the wider coiled part resembles the wide tube described 

 by him. The vesicle also is extremely thin walled, and appa- 

 rently com^DOsed of a single layer of irregular muscle cells lined 

 by very thin epithelial cells. The opening of the vesicle to the 

 exterior is extremely well-marked, the lining of the vesicle 

 distinctly changing from flattened to cubic epithelial cells, 

 whicli. in their turn, give place to the columnar cells continuous 

 with those of the external surface of the body [Fig. 21] and, like 

 them, covered by a thin cuticle. The arrangement of the 

 muscles is characteristic, as. In addition to the ordinar}- circular 

 and longitudinal muscle bands, there is a distinct group of 

 muscle fibres round the external opening, which appears to 

 form a " sphincter '' controlling the opening of the nephridium 

 to the exterior [Fig. 21]. 



