NERINE. 



141 



alimentary canal in this region is a flattened tube with the dorsal and ventral vessels 

 above and below. 



The segmental organ lies to the exterior of the outer pennate fold of the ventral 

 longitudinal muscle. 



Behind the foregoing the vertical muscles diminish, and then almost disappear, the 

 dorsal and ventral longitudinal muscles becoming solid layers, the dorsal with its thickest 

 edge on each side of the middle V-shaped internal, the massive internal borders of the 

 ventral being more widely separated, and having between them circular fibres, and above 

 this a band of longitudinal fibres on each side of the ventral vessel, with fibres from the 

 alimentary canal. The hypoderm is thickened over a broad area in the mid-ventral line, 



T\C 



ac. 



Fig. 113.— Transverse section of the body-wall of the anterior region of Nerine folio sa, Sars. 

 vert. m. Vertical muscular bands. 



and the single neural canal is smaller, and situated at the upper part of the nerve-area. 

 The pennate folds of dorsal and ventral longitudinal muscles have disappeared. The 

 alimentary canal has a much thicker layer of longitudinal muscle-fibres externally with a 

 circular coat beneath, and the thick mucous layer has smaller cells. 



In Nerine foliosa the bright red blood is driven from the tail forward in the dorsal 

 vessel, which sends off in each segment a trunk to the branchiae, the aerated blood 

 descending by the branch joining the ventral. There is no special provision for thrusting 

 out the proboscis as in Magelona since Nerine bores with its pointed snout and muscular 

 body. 



In Nerine cirratulas the nerve-cords, after meeting in the mid-ventral line, are 

 proportionally larger, and the preparations show a distinct neural canal toward the lower 

 part of each. The ventral longitudinal muscles are also more compact anteriorly, whilst 

 the dorsal taper to a thin arch superiorly. The alimentary canal anteriorly has deep 

 folds and ridges of its mucous membrane. In the median line ventrally are a central and 



