232 



As to the significauce of the facts here reeorded for more gene- 

 ral phylogenetic speculations concerning the archaic condition of 

 the nephridia in earthworms , this has not beeu touched upon by 

 Borelli is his paper above mentioned. Nor ara I prepared to go 

 into this subject at any length not being acquainted by personal 

 observation with a sufficiënt number of representatives ofthediöe- 

 rent genera. Still I may be allowed to remark that in the latest 

 paper by Benham on the nephridium of Lumbricus (Quart. journ. 

 of mier. science, vol. 33, p. 293) the question is discussed at 

 some length whether the » plectronephric" arrangement of the 

 nephridia is the more archaic condition, or the »meganephric". 

 Beddard and Spencer have adopted the former view, Benham is 

 inclined to side with them , whereas Ray Lankester and Horst 

 have argued in defence of the second proposition. 



Benham writes (1. c. p. 314). »The assumption that the mega- 

 »nephric condition is archaic would, 1 think, plunge us into a 

 »sea of difiBculties ; for if a large nephridium is the more primi- 

 »tive, then we have to explain how it comes about that in some 

 » genera and species the paired nephridiae are in relation to the 

 » inner couple of setae, and that in others they are in relation 

 » to the outer couple ; how it is that in some worms , e. g. Perio- 

 »nyx saltans and Acanthodrilus novae-zelandiae , the position of 

 »the nephridiopores alternates from segment to segment? and 

 »finally how can we explain the presence of two pairs of nephri- 

 »dia per segment in Brachydrilus? For if a large nephridium is 

 »ancestral, was there but a single pair, or two pairs or four pairs?" 



The relation of the paired nephridia in various genera to the 

 different couples of setae alluded to by Benham appears in a diffe- 

 rent light, now that it has been settled that this relation is not 

 only not constant in the common earthworm , but that the very 

 inconstancy offers features which might plead in favour of the 

 hypothesis that two pairs of large nephridia (perhaps even three) 

 were originally contained in each segment and that of these two 

 pairs one had its nephridiopore above the outer, the other above 

 the inner couple of setae. 



