AN ATTEMPT TO CLASSIFY BAETHWORMS. 209 



The possession by earthworms either (1) of such a network 

 or " tuft" of small tubules (a " plecto-nephric " condition), or 

 (2) of a pair (rarely two pairs) of large " nephridia '' (a 

 '^ mega-nephric " condition), suggested to me the possibility of 

 dividing the earthworms into two groups, according to con- 

 ditions of the excretory system. This has formed the basis of 

 the classification here put forward ; but we are instantly met 

 by the fact that some species of certain genera comprised in 

 the first set — i. e. those with a network of small tubules — have 

 apparently large " nephridia ; '^ but is this really the case ? 



Both in Acanthodrilus and in Perichseta species 

 have been originally described as having large nephridia ; but 

 a renewed and more careful microscopical examination has 

 proved either that this large nephridium is accompanied by a 

 network of tubules as in P. arm at a (Beddard), or that 

 the supposed " nephridium " really consists of a mass 

 or tuft of small tubules as in Ac. multiporus. So 

 that when Fletcher states that several species of Crypto- 

 drilus, a genus which is usually " plecto-nephric,^^ have three 

 pairs of large " nephridia " per somite, I think we are justified 

 in assuming that these will turn out to belong to one or other 

 of the above categories.^ I may add that Fletcher's descrip- 

 tions of numerous species are unaccompanied by figures, 

 except in a few instances of external characters. 



The genus Perionyx, formed by Perrier for the reception 

 of a worm very similar to Perichaeta, has always been closely 

 associated with this latter genus, and I feel considerable hesi- 

 tation in removing it from association with Perichseta; but 

 it differs from the latter in possessing a pair of large nephridia 

 in each somite unaccompanied by smaller tubules, as well as in 

 some other small details. This I have ascertained by the 

 examination of sections, and by mounting a portion of the 

 body-wall, with nephridia, complete. 



' Beddard has recently ('Quart. Journ. Micr. Sci.,' xxx, Feb.), described 

 these new species of Acanthodrilus, in which only large nephridia are 

 mentioned. Here again, I think, we may suspect that a network of small 

 tubules is present in addition. 



