CCELOM AND RENAL ORGANS 33 



tubules of Vertebrata, and later the renal tubes discovered by 

 Sanger and Balfour in Peripatus, and the various excretory and 

 genital ducts of other Arthropoda. The name " nephridia " 

 became very generally adopted by morphologists for all of these 

 structures. 



It appears, however, that this generalisation was too sweeping, 

 as has been pointed out by Mr. E. S. Goodrich, who has extended 

 to the Coelomocoela in general the conclusions drawn by Prof. Ed. 

 Meyer from a study of the development of the Polychseta (Meyer, 

 "Die abstammung der Anneliden," Biolog. Centralblatt. vol. x. 

 1890). We have, in fact, hitherto included under the name " neph- 

 ridium " two quite distinct kinds of renal excretory tubules — the 

 one derived from single cells ultimately though not always actually 

 traceable to ectoderm, the other nothing more than a portion of 

 the coelom itself communicating by a pore with the exterior. To 

 the first category belongs the type-nephridium — namely, that of 

 the Earthworm, and with it go similar tubules in other Oligochaeta 

 and Polychfeta, and the excretory systems of Plat3''helmia and Roti- 

 fera. Hence, for these the name " nephridium " must be retained. 

 To the second category belong the peritoneal funnels of many 

 Choetopoda, the funnel-like generative ducts of Oligochseta, the 

 whole series of so-called nephridia, modified and unmodified, in 

 Arthropoda, the renal sacs of Mollusca, and the peritoneal funnels 

 and connected tubules, whether of renal or gonoduct significance, 

 in the Vertebrata. The origin of these structures as jmrts of the 

 coelom itself suggests the name of " ccelomic funnels " for them. 

 The excretory activity of the wall of the coelom and of these 

 specialised parts of it was, it must be supposed, acquired ajler the 

 first development of such conduits and pores to sei've as exits for 

 the genital products from the coelom. The name " coelomoduct " 

 is proposed now for the first time as the best general term for 

 these passages. Coelomoducts are to be contrasted with nephridia ; 

 formerly they were confused with them. Coelomoducts are parts 

 of the ccelomic wall itself ; nephridia are ingrowths from a 

 superficial nephroblast. In the Mollusca we find embryonic, 

 evanescent renal organs which are nephridia (Pulmonata) ; these 

 disappear and are succeeded by permanent renal organs which are 

 crelomoducts. 



Nephridia do not always open into the coelom, e.g. those of 

 Platyhelmia where the generative sacs are all that represents 

 coelom. Ccelomoducfs necessarily open into the coelom at some 

 stage of their formation if not permanently, since they are part of 

 it. They do not necessarily open directly or indirectly to the 

 exterior, though they usually do so directly. 



In the marine Choetopoda, according to the observations of 

 Meyer and Goodrich (Quart. Journ. Micr. Sci. 1899), there is often 



3 



