STRUCTURE OF EARTHWORM ALLIED TO NEMERTODRILUS. 575 



it passes. The duct is not embedded in the longitudinal 

 muscular coat or in the peritoneum^ but appears to lie in the 

 coelom. 



If this duct had turned up two or three years earlier than it 

 haSj I should have been able to claim it as a discovery of some 

 importance. The account given by Balfour of Hatchek's state- 

 ments about the developing nephridia of Criodrilus gave 

 additional strength to them, although Balfour considered them 

 to need confirmation, and the apparent confirmation which is 

 given by a young, only just out, foetal earthworm would have 

 almost clinched the matter. The discovery even of Meyer and 

 Cunningham that the adult Terebella conchilega is fur- 

 nished with such a longitudinal duct was regarded of the 

 greatest importance in that connection. As it is, the new 

 fact recorded here has lost a good deal of importance by appear- 

 ing too late. Since Hatchek's paper the aspect of the nephri- 

 dial question has changed. Nevertheless it is of some little 

 importance. In Perichseta there does not appear to be, in 

 the adult at any rate, a pair of distinct longitudinal ducts 

 passing from segment to segment ; there is simply the irregular 

 network of each segment which is connected here and there 

 with that of adjoining segments. Spencer, however, has 

 described (9) in Megascolides aus trails a pair of longitu- 

 dinal ducts which run from segment to segment, putting the 

 complicated nephridial network and the large paired nephridia 

 of successive segments into direct communication. It is not yet 

 known how early these ducts appear in Megascolides, but 

 it is interesting to notice that they appear at least compara- 

 tively early in the development of Libyodrilus. In the adult 

 worm they persist (fig. 7), but their importance is lost in the 

 complications of integumental network. For all that I know 

 the paired longitudinal ducts may be the first of the nephridial 

 system to appear. I very much regret that my material does 

 not enable me to settle this question. At any rate, it is certain 

 that in Libyodrilus the integumental network con- 

 nected with the paired nephridia is preceded by 

 paired longitudinal ducts uniting those nephridia. 



