i9o8.] EXCRETORY ORGANS OF METAZOA. 569 



of the two he considered to have this relation. Similar results were 

 reached by Bergh (1886), Roule (1889) and Beddard (1892). 

 Lehmann (1887) opposed the idea of homodynamy on the grounds: 

 (i) That two pairs of nephridia to a segment is not typical; (2) 

 that in the embryo nephridia develop in the genital segments ; 

 and (3) that the genital ducts arise later than the nephridia. Finally 

 there may be mentioned the view of Benham (1904) according to 

 whom the phylogenetic series is as follows : ( i ) The nephridia 

 acted as genital ducts; then (2) a special coelomostome became 

 added to the nephridia, forming a nephromixium ; finally (3) the 

 coelomostome formed " its own coelomo-duct, which may either co- 

 exist in the genital segment with the nephridium (as in most ' terri- 

 coline ' Oligochastes), or the nephridium . . . disappears from the 

 segment during or before the development of the genital duct (as 

 in ' limicoline ' Oligochastes and Protodrilus). We have, then, to 

 some extent a parallel series of phenomena analogous to thbse de- 

 scribed wath so much care by Goodrich in the Polychaeta." 



There is much in these relations that is still puzzling. But at 

 least the funnels of both organs seem to be homodynamous since 

 they have an approximately similar mode of growth. In the 

 Lumbricids the two organs of a genital segment might well have 

 arisen, as Balfour intimated, as division products of a common 

 embryonic anlage. And in those species where nephridia are want- 

 ing in the genital segments, the genital ducts, as Vejdovsky arguea, 

 are to be considered as in part at least modifications of the nephridia 

 of such segments. 



Chloragogue {Pericardial Gland). — This is peritoneal in origin 

 and particularly excretory (Grobben, 1888, Rice, 1902, Rosa, 1903a ). 



Peritoneum and Cwlomic Fluid. — These have been considered 

 excretory by Grobben (1888), who holds that the coelomic fluid is 

 in great part an excretory product though at the same time it has 

 the functions of blood and lymph. 



Other Excretory Organs. — Here are to be reckoned the bacter- 

 oidic cells of the connective tissues, the yellow cells of the intestine, 

 and the amoebocytes of the blood (Cuenot, 1897). 



PROC. AMER. PHIL. SOC, XLVII. I90 KK, PRINTED JANUARY I4, I909. 



