Ui Piuf. M'liitosli on the 



intervals, during- tlie boring operations of the animal, as a 

 pinkish distensible sac, which, especially in partial extrusion, 

 often presents a most regularly rugose appearance. In 

 complete expulsion the general form is that of a reddish 

 apple marked with flattened ribs, which run from the deep 

 dimple at the apex to the base. At the upper part of the 

 protruded organ is a somewhat elongated conical smooth 

 portion, marked only by the fine longitudinal lines of the 

 retractor muscle and not by ribs. The blood chiefly occupies 

 the upper and middle regions, but this is due to position, 

 since there is no reason why it should not enter any hollow 

 portion of the extruded organ. AVithin the body of the 

 animal it forms a longitudinally folded sac continuous 

 anteriorly with the great transverse inferior lip, and placed 

 along the ventral region of the body- cavity, below the 

 digestive system. Posteriorly it ends in a cul de sac, to the 

 sides and tern)ination of which the great muscular retractor 

 is attached. The upper and anterior fold, again, is con- 

 tinuous with the buccal mucous surface, so that in extrusion 

 an uninterrupted rim is found at the sides, while the centre 

 of the alimentary canal is blocked by tlie outward folds of 

 the pharynx, the protrusion of the proboscis being thus 

 inimical to swallowing; indeed the functions of the organ 

 are not digestive. 



In partial protrusion the proboscis under pressure presents 

 a series of somewhat radiated lines — due to the prominent 

 chitinous folds of its lining membrane, in which no pores 

 have been made out. The fibres of the short and long 

 retractors spread out in the central region, and the organ is 

 crossed by the fibres of the circular coat. The fibres of the 

 short retractors, which pass from the dorsal raphe on each 

 side of the body-wall, expand in a fan-like manner, chiefly 

 at the basal part of the extruded organ, and therefore in the 

 retracted condition are connected with its anterior region ; 

 while the fibres of the long retractor spread over a wider 

 area, for the most part toward the outer part of the organ 

 in protrusion, and thus in retraction are attached to the 

 posterior region. In extreme protrusion it forms a large 

 flattened bag, which does not quite reach the tip of the 

 snout. Externally, and especially at the tip in extrusion, is 

 the dense chitinous coat, continuous with that of the mouth 

 superiorly, and with the cuticle at the transverse fold or 

 lower lip inferiorly : beneath is a streaked granular layer 

 homologous with the hypoderm of the body-wall; indeed, 

 continuous with it. In partial protrusion this coat follows 

 the previous in forming numerous elevated ridges and folds — 



