366 ORGANS OF DIGESTION. 



food to the mouth are produced, as in other conchifera, and 

 in tunicata, by the vibratile cilia disposed on the branchial 

 folds (A., b.} and on the surface of the mantle (A. i.) en- 

 veloping the respiratory cavity. The very long labial 

 tentacula of the pinna nobilis (Fig. 1 20. E. b.) extend late- 

 rally from the lobed margin of the mouth (E. .), and are 

 striated like branchiae on their inner surface. The short 

 narrow oesophagus (E. c.) leads to an elongated stomach, wide 

 at its cardiac portion (E. d.), and narrow and valvular at its 

 pyloric end (E. c.), where it forms a small round caecum. A 

 distinct pyloric valve (120. G. b.) is formed by a circular fold 

 of the mucous coat at the angular junction of the stomach 

 (120. G. a.) with the small intestine (120. G. c.), as in most 

 mollusca and fishes. On opening the cavity of the stomach, 

 strong muscular bands (120. C. c.) are seen around its 

 pyloric portion, and several large oblique apertures (120. C. 

 d. e.) leading into the lobes of the liver are found near to the 

 duodenum (120. C. a.). The curved duodenal portion pre- 

 sents a considerable enlargement (120. E. /'.), and a similar 

 dilatation is observed near the end of the colon (120. E. g.} 

 as in many insects. The colon of the conchifera generally 

 pierces the ventricle of the heart or the commencement of 

 the two aortas, and passes longitudinally through their cavity. 

 The part of the intestine which traverses the heart, and the 

 portion imbedded in the substance of the liver are commonly 

 found to contain food when the rest of the canal is empty. 

 The stomach of several of these animals is frequently ob- 

 served filled with mucus, sand and mud, as if they merely 

 strained the agitated waters of their turbid contents to obtain 

 their food, as the echinoderma and amielides mostly obtain 

 their nutriment by passing the sands of the bottom of the 

 sea through their intestine. The liver presents diversities of 

 conformation in this class as among the tunicata. In the 

 mactra the bile enters the stomach by a single wide duct, as 

 in the cephalopods, and the component coeca or biliary 

 tubuli are large and distinct. From the simple condition of 

 the liver in the conchifera, the numerous minute tubuli biliferi 

 which compose its lobes are easily rendered perceptible by 

 removing the peritoneal covering, and floating a small de- 

 tached portion in water, as seen at (120. H.) In most conchifera 

 the convolutions of the intestine are contained in an abdo- 



