88 KARM NARAYAN BAHL 



sich offenbar die Lappchen bei den mit " Plectonephridien " 

 versehenen Oligochaeten und in den vorderen Segmenten 

 von Megascolides. In den hinteren Begmenten des genann- 

 ten Eiesenregenwurmes reduciren sich die Lappchen an einige 

 grossere, welche der Lage nach den Schhngen am Nophridium 

 von Lumbricus entsprechen.' Vejdovsky's conclusions 

 are based on his researches on Rhy nchelmis, in which 

 a definite pronephridial stage precedes the permanent nephridia, 

 and on the development of nephridia in Megascolides, 

 in which a paired pronephridial condition precedes the per- 

 manent plectonephric system. 



The facts of nephridial development recorded in this paper 

 do not lend themselves to Vejdovsky's interpretation of the 

 evolution of the excretory system. In the first place, we cannot 

 distinguish in the development of Pheretima a pronephridial 

 stage as distinguished from a stage of permanent nephridia. 

 What we do get is a paired condition in the embryo which goes 

 to form part of the adult system and is not entirely superseded 

 by it. Secondly, the paired nephridia themselves are not 

 transformed, as they are in Megascolides, into the diffuse 

 system of the adult, but numerous nephridia arise indepen- 

 dently to be added to the primary integumentary nephridia. 

 In the third place, the adult Pheretima does not show the 

 condition referred to by Vejdovsky in some other worms 

 (' Eiesenregenwurmes '), where the anterior segments have 

 numerous nephridia but the posterior ones show the paired 

 meganephric condition . 



Since the diffuse and paired forms of the excretory system 

 occur in genera which are so nearly related, Beddard (3) thinks 

 there can be no profound gap between the two kinds of organs. 

 But when one takes into account the fact that in the family 

 Perichaetidae, Pleionogaster possesses nephridia of 

 the diffuse type all opening to the exterior, Megascolex 

 has a pair of large nephridia in each segment in addition to 

 the small scattered nephridia, wiiile P e r i o n y x and D i p o r o- 

 chaeta have only large paired nephridia, it becomes very 

 difficult to think of and offer an explanation for the intermediate 



