574 OLIGOCHAETA 



In all the genera of the family the setae are paired, and are of the common 

 sigmoid form found in the majority of the terrestrial Oligochaeta ^. The individual 

 setae of each pair may be nearer or further away from each other, but there are 

 never more than eight of them in a segment. 



The dorsal pores appear to be absent, except in Platydrilus and EvAriloides.' 



The integument very generally, though not always, contains peculiar bodies, 

 possiHy of a sensory nature, whose structure has been fully described on p. 16 

 above. These organs have never been met with outside this family. In many 

 Eudrilidae the oesophagus is furnished with median ventral diverticula, unknown in 

 any other group- except in the genus Gordiodrilus, belonging to quite a different 

 family. These diverticula, which were first made known by myself (in Eudrilus), 

 are not simple pouches ; the lumen is converted into a network of narrow canals 

 by the folding and anastomosing of the lining epithelium ; this may even be developed 

 to such an extent as to produce in parts an intra-cellular lumen. Paired calciferous 

 glands, in addition to these ' Chylus-taschen,' as they have been termed by Michaelsen, 

 are commonly present ; all of these structures may be absent ; in Libyodrilus, for 

 example, there are neither calciferous glands nor ventral diverticula. In other 

 genera the calciferous glands are apparently represented by peculiar structures, whose 

 minute anatomy and relations have been dealt with on p. 6%. 



Another highly characteristic feature in the organization of the Eudrilidae is 

 a peculiar modification of the excretory system. This is not seen in all the genera 

 of the family, but occurs in Libyodrilus, and, apparently in Pareudrilus, Stuhlmannia, 

 and Eudriloides. The peculiarity consists in the formation of a network of complex 

 character out of the nephridial ducts ; this network traverses the body- wall, and there 

 are numerous orifices into the exterior. Characteristic though it is of one family of 

 the Oligochaeta, and of one family only, I have thought it necessary to regard this 

 remarkable condition of the excretory system as of sufficient general importance to 

 find a place in my general sketch of the organization of the Oligochaeta (see p. 44). 



The most characteristic feature of the family, however, is the arrangement of the 

 genital organs. 



As in most other families of earthworms, we find species with only a single 

 pair of testes, and other species, the majority, in which there are the more usual 

 two pairs ; exceptionally (in Hyperiodrilus) the testes are attached to the posterior 

 wall of their segments, which are always the tenth and eleventh. Quite unique 

 among Oligochaeta is the arrangement of the funnels and the first part of the 

 sperm-ducts in certain forms ; in Eudrilus, as was first described by myself, the 



* In StiMmannia lariaiUin only is the free extremity ornamented. 



