Gathj Marine Laboraior//, St. Andrews. 251 



pennate aspect iu longitudinal section or a series of straight 

 or curved transverse l)ai's, according as the long tube is cut 

 in a median or lateral plane (PI. X. fig. 19). In the former 

 case a central axis of the secretion is flanked on either t>idc 

 by a series of plates, often slanting distally^ and containing 

 an occasional nucleated cell or a series of granules in the 

 plate. Such a condition may be due to the action of the 

 preservative spirit, or to the method of secretion, but it is 

 worthy of note. The slender posterior ends of these glands 

 are curved forward and outward. The secretion forms a 

 lining to the tube, and attaches foreign structures such as 

 sand-particles and foraminifera to it externally ; and in 

 many cases, so firmly do the annelids adhere to it after 

 preservation, that rupture of the tissues accompanies their 

 removal. 



The hypoderni coverii)g the mouth and buccal region, 

 including the •'lip-organ," differs from that on the surface 

 of the body and branchise. It is bounded by a uniform and 

 definite investment, and has a finely-granular and fibrillar 

 structure, so that it forms a tougher, more massive, and 

 more consistent layer, which, however, at certain parts 

 diminishes in thickness as it approaches the branchise. It 

 rests on a basement-layer having beneath it a complex series 

 of muscular fibres. The same kind of hypoderm dips down 

 and envelops the lip-organ, though it is more translucent 

 in section, from the paucity of granules which stain more 

 deeply. Then the organ forms a deep furrow (PI. VII. fig. 6) 

 with massive pale walls, whilst a double fold which now 

 appears to the inner side, as well as the folds dorsad of the 

 mouth, stain distinctly, as also do all the folds of the mouth 

 and pharynx. The pale region thus lies in the figure between 

 a and a in the centre of the organ, but it thins off on each 

 side — that is to say, the middle region of the fold has thickest 

 ■walls. The buccal mucous membrane is like that first men- 

 tioned in the lateral area of the cephalic region, viz., closely 

 fibrous and granular, and it continues to the second dia- 

 phragm. It rests on a basement-membrane and a firm 

 outer layer of both circular and longitudinal muscular fibres, 

 the anterior or buccal region having numerous trabeculse 

 fixing it to the body-wall ; and this is specially marked at 

 the thick pale folds (lip-organ, Ip., in the various figures). 

 The anterior buccal region is probably capable of partial 

 protrusion. In front of the second diaphragm the folds of 

 the canal have thick muscular walls, so that a certain amount 

 of difierentiation exists — either as proventriculus or stomach. 

 Behind the second dissepiment the Avails of the canal are 



17^ 



