440 Prof. M'Intosli on the 



swim freely in tlie water in a wriggling manner ; indeed, 

 when fresh, its vivacity is remarkable. 



III. The Digestive System. 



The mouth opens at the base of the flattened snout as a 

 somewhat triangular or T-shaped slit surrounded by lips of 

 raucous membrane, and situated between or very slightly in 

 front of the bases of the tentacles. The anterior lip is 

 sinuous but complete, while inferiorly is a wide fissure 

 (bounded laterally by prominent margins) which runs a 

 considerable distance backward. The lips are very mobile, 

 and in life frequently expand to gulp water, a feature 

 common in the Spionidae, but of importance, in relation to 

 the blood-channels in the neighbourhood, in this form. 



The alimentary region behind the mouth is somewhat 

 complex, and may be divided into pharynx, proboscis, 

 oesophagus, and intestine. In using these terms, however, 

 no special weight is placed on them, though it is probable 

 that the barred region of the pharynx is homologous with 

 the proventriculus of the Syllidse and others; while the 

 oesophageal division may consist of gullet and ventricule 

 combined. In the retracted condition of the proboscis the 

 general arrangement is as follows : — The buccal leads into a 

 pharyngeal division, which is thrown into numerous prominent 

 rugse, especially posteriorly, and it is further characterized by 

 the muscularity of its walls. To this region is appended the 

 protrusible proboscis in a manner afterwards to be explained. 

 Behind the pharyngeal is the oesophageal division, which 

 continues to the ninth body-segment and terminates in the 

 intestinal region proper. 



It has already been noticed that the hypodermic tissue of 

 the ventral surface of the snout becomes greatly hyper- 

 trophied in the median region throughout a considerable area 

 in front of the mouth. It is especially deep anterior to the 

 space for the transverse miUscle, and at the space may fairly 

 he said to assume the lax translucent character distinctive of 

 the alimentary modification. In longitudinal sections the 

 point of separation is recognized by the thinness of the 

 cuticle. Externally is a distinct layer of transparent chiti- 

 nous tissue continuous w^ith, though much thinner than, the 

 cuticle, then a series of granular and rather translucent 

 gland-cells between the former and the basement-tissue. 

 The buccal folds occupy a large area in protrusion of the 

 proboscis at the point of separation of the dorsal transverse 

 muscle, and they are somewhat symmetrically arranged. 



