i84 OLIGOCHAETA 



.he dilatations on the sperm-ducts and the peculiar sense organs of the integument 

 yhich. also characterize these genera are absolutely distinctive of them and have not 

 iheir counterpart in any other group of Oligochaeta. 



We can hardly escape from the difficulties of arranging the various genera of 

 Eudrilidae in their relative positions by the assumption that the family is diphyletic 

 —a proceeding which often affords relief to the perplexed systematist. In spite of 

 ihe well-marked differences which divide certain genera, and which may allow of 

 iheir being divided into two subfamilies, there is too broad a basis of agreement 

 'or any such course to recommend itself; it does, however, appear that the group 

 ivhich is represented by Stuhiviannia and its immediate allies, has arisen from the 

 main stem near to its root, before some of the characteristic features of the other 

 jroup have been produced ; I refer more particularly to the median oesophageal 

 pouches, and to the integumental sense , organs. If this view be adopted the 

 primitive form of Eudrilid may be supposed to have possessed a series of paired 

 3alciferous glands occupying a number of segments, a single or perhaps two sperma- 

 thecal pouches, opening on to the exterior on the thirteenth segment or thereabouts, 

 of epidermic origin, in fact, showing those characters which now are common to the 

 two subfamilies of the Eudrilidae. In this primitive form we must assume that 

 there was no development of sacs surrounding the ovaries. Eudriloides and Platy- 

 irilus will be the nearest to the ancestral form on one line ; on the other line of 

 development there is no form left which stands near to the ancestor ; the nearest 

 should be, as I have already suggested, Heliodrilus. We must, therefore, I consider, 

 place the Eudrilidae in two parallel lines. 



Affinities of Eudrilidae. 



The relationships of the Eudrilidae to other families of Oligochaeta are not at 

 all plain. Rosa, at first included them with what I term here the Cryptodrilidae ; 

 but at the time when he wrote the only Eudrilid known was Eudrilus itself; the 

 existence of only a single abnormal genus might reasonably be held to render a 

 further division unnecessary. This view of the affinities of the Eudrilidae was, 

 however, adhered to by Benham (1) a year or two later. It is now agreed that 

 the Eudrihdae form a distinct family. This being so, what are their affinities? We 

 may clear the way by placing in a tabular form the salient peculiarities of the 

 family. The Eudrilidae, to a greater or less extent, are distinguished by the following 

 characters restricted to themselves : — 



(i) The presence of sense organs (?) like Pacinian bodies in the skin. 



