320 W. BLAXLAND BENHAM. 



out on each side to a very considerable extent, so as to be two 

 or three times as wide from side to side as from front to back. 

 Even with such scanty details as we have, I think it is 

 possible to trace a few stages in the evolution of the compli- 

 cated funnel of Lumbricus, Rhinodrilus, &c. Starting 

 with the nephrostome of the Enchytrseidse, for example, we 

 have a funnel formed merely by the terminal perforated cell 

 without accessory marginal cells (see PL XXIV, figs. 27, 28, 

 29, a). By the subdivision of this cell, as in the ontogeny of 

 Stylaria, the lip of the aperture is formed by two cells (as is 

 the case also in Clepsine amongst the leeches) ; in Tubifex 

 also two or a few more (a similar increase is observed in 

 Pontobdella). In Rhynchelmis — one of the nearest of 

 the waterworms to earthworms — eight marginal cells have 

 become formed, as is the case, too, in Per. malamaniensis 

 (PI. XXIV, fig. 25) ; now a differentiation occurs amongst 

 the cells, as in P. aspergillum. In Urochseta, in the 

 peptonephrostome, not only have the marginal cells greatly 

 increased in number, but the intra-cellular tube is dilated (see 

 diagram, PL XXIV, fig. 25, b), so as to increase the effect of 

 the ciliated margin. Suppose this dilatation were carried 

 further, so that the sides diverge, the '^perforated cells" 

 would become " grooved cells," and would lie between the 

 intra-cellular tube and the marginal cells (diagram, fig. 25, c). 

 I am not sure that any of the earthworms studied correspond 

 to this stage. A little further differentiation, by a still further 

 divergence and an outward curve of the " grooved cells," leads 

 on to the stage presented to us by Rhinodrilus and Lum- 

 bricus (cf. diagram, fig. 25, d, with PL XXIII, fig. 4). 

 These large nephrostomes replace the numerous small ones of 

 Perichseta, such being evidently more efficient for the removal 

 of phagocytes than is the smaller funnel of the latter genus. 



5. The Vascular Supply of the Nephridium. 

 The living nephridium of an earthworm is a remarkably 

 beautiful object when viewed under a moderately high power; 

 and this is due to the delicate and complex network of blood- 



