52 KARM NARAYAN BAHL 



arising not from the ' funnel-cell ' (' Trichterzelle ') but from 

 a j)eritoneal cell. 



This view of the mesodermal or the so-called ' intraperitoneal ' 

 origin of nephridia is in strong contrast with that held by 

 Hatschek, Wilson, Meyer, and Vejdovsky (in his later work), 

 which ascribes an ectodermal or a ' retroperitoneal ' origin to 

 the main body of the nephridium and traces the ' funnel-cell ' 

 to the primary nephric row. According to this view the ' funnel- 

 cell ' arises from the primitive cell-row, or nephric cord, formed 

 by the repeated division of one of the teloblasts on either side. 

 In the earlier stages, this teloblast and the nephric cord to 

 which it gives rise lie on the surface of the embryo ; thus the 

 ' funnel-cells ' are epiblastic in origin. From the nephric row 

 one cell enlarges and enters into connexion with each successive 

 segment ; these large cells, arranged inetamerically outside 

 and between each pair of somites, are the so-called ' funnel- 

 cells '. In some worms, like Dendrobaena and Lum- 

 b r i c u s , the ' funnel-cells ' give off the chain of posterior cells 

 whilst separating from the nephric row, thus remaining for 

 some time in connexion with it. In other cases, such as 

 Oriodrilus, the ' funnel-cells ' appear to separate first (9). 



This view of the superficial origin of nephridia was strongly 

 supported by Goodrich's work (10), in which he showed that 

 in certain Polychaetes (e.g. Nephthys) the nephridia do not 

 open into the coelom at all, but terminate internally in a bunch 

 of solenocytes which project into the coelom. He regarded 

 the nephridium as essentially an ectodermic structure com- 

 parable with the excretory tube of a Nemertine or of a Platy- 

 helminth. According to him the excretory organs of Oligo- 

 chaeta are ' true ' nephridia, i.e. tubes originally blind which 

 have acquired secondary communications "vnth the coelom, 

 as distinguished from the ' coelomoducts ", the term he uses 

 for purely mesodermal structures. He points to the co-existence 

 of the genital duct (which is a wide short coelomoduct) and the 

 nephridium in the same somite, in Lumbricus, as evidence 

 that the two structures cannot be homologous with one 

 another (12). 



'o^ 



