No. 3-] THE DISCODRILID NEPHRIDIUM. 36 1 



chlorogogen layer extends far forwards. In such worms 

 nephridia are absent from the genital somites, and the genital 

 ducts have widely open mouths suitable for conducting away 

 the coelomic fluid. The funnels are sometimes glandular 

 (Enchy traeidae) . In the higher, mostly terrestrial Oligochaeta, 

 nephridia are frequently present in the genital somites, but the 

 male ducts are frequently cut off from communication with the 

 general coelom by being enclosed in spermatic vesicles, periodi- 

 cally at least. The nephridial funnels are more highly special- 

 ized for producing currents in the coelomic fluid, but the 

 absence of chlorogogen cells in this region leads one to believe 

 that the fluid may here be simply watery, without excreta, and 

 serve in the nephridium the purpose of flushing the tubules, as 

 does the fluid secreted by the Malpighian vesicle in the verte- 

 brate kidney tubule. An elaborate blood supply transfers the 

 source of waste substances supplied to the nephridium largely 

 from the coelomic fluid to the blood. Posterior to this region 

 the conditions are changed, for here the chlorogogen cells are 

 abundantly developed, but the dorsal pores, more constantly 

 developed in this region than anteriorly, offer a means of exit 

 to the surplus fluid and excreta which they pass into the coelom. 

 Beddard (1) has already suggested the probable excretory func- 

 tion of the dorsal pores, but the other function, that of assisting 

 to moisten the surface of the body, which has been assigned to 

 them, is doubtless equally important, as this has been shown 

 by Whitman (35) and others to be the final disposition of the 

 fluid accumulated by the nephridia of certain leeches. 



The condition of the Hirudinea is especially interesting. 

 Here we find in very close relation to the decreasing impor- 

 tance of the coelom, and of the coelomic fluid as a means to 

 excretion, a frequent occlusion of the nephrostomata, a won- 

 derfully rich nephridial blood supply, and a closure of the 

 coelomic ends of the vasa deferentia, owing to continuity with 

 the testes. Here, of course, the testes and nephridia are 

 developed metamerically side by side. The almost exclusively 

 coelomic excretion of the Polychaeta, associated with the utili- 

 zation of the nephridia as genital ducts, needs also to be 

 mentioned. 



