STRUCTURE OF EARTHWORM ALLIED TO NEMERTODRILUS. 551 



described by myself in Eudrilus; as they occur in Libyo- 

 drilus they will probably prove to be characteristic of the 

 family. Similar vessels appear to occur in other earthworms, 

 but their distribution has not been much studied. In Libyo- 

 drilus as in Eudrilus they are paired trunks, but 

 they do not unite together at intervals as in the latter genus. 

 These vessels are, like the supra- oesophageal (supra-intestinal) 

 trunk, concerned with the blood supply of the oesophagus ; they 

 are probably efferent trunks, taking the blood away from the 

 oesophagus, which has reached it by way of the supra-oesopha- 

 geal vessel. 



Two mesenteries are connected with these vessels 

 and with the ventral oesophageal wall; these enclose 

 a space which appears to be completely shut off from 

 the coelom of the segments. The arrangement of these 

 mesenteries differs in different parts of each segment. Towards 

 the middle of the segment, as is shown in fig. 17, the two 

 mesenteries originate from the lateral regions of the oesophagus 

 (the histological details of the oesophagus are not shown in the 

 figure) ; they are thrown into folds by the contraction caused 

 by the preserving fluid. These mesenteries unite considerably 

 above the ventral blood-vessel, and thus enclose a space which 

 is roughly crescentic in outline but of considerable vertical 

 depth. The membrane consists of a faintly staining nearly 

 homogeneous core, covered on both sides by peritoneal cells, 

 of which the nuclei were alone visible ; here and there small 

 groups of longitudinally running bands of muscular fibres, not 

 shown in the figure cited, are embedded in this homogeneous 

 layer. The figure, however, does show two longitudinally 

 running bands of muscle {m) ; these are special muscles 

 attaching the ventral surface of the oesophagus either to the 

 septa or to the ventral parietes. Above these, i. e. nearer to the 

 oesophageal wall, are the paired sub-oesophageal trunks {bl.ves.); 

 in the section represented in the figure the two blood-vessels 

 are seen to be attached to the mesenteries, but in other sec- 

 tions they lie freely within the mesenteries, and further back 

 they may come to lie outside. These facts appear to show that 



