COXCHLFEROUS MOLLUSCA. 



167 



two turns through the body, terminating in the rectum 

 ;it the posterior border of the shell ; the liver (i) is very 



surrounding the 



ive tube, and the 

 biliary ducts open into 

 the stomach, as in the 

 tunicata ; the large 

 branchial leaflets (h, 



respiration are 

 covered by the mantle 

 (/); in them we find 

 the cells for lodging 

 the ova ; the adductor 

 muscle (G, H) serves 

 for closing the valves 

 of the shell, and at 

 its internal side is seen 

 the heart (i). 



[ 320. The GAS- 



:-ODA possess 

 more perfect organs 

 of prehension than Fi S- 1/6. The anatomy of the Ostrea edulis. 

 the preceding class ; here we find not only complicated tubes 

 for absorbing, but likewise organs for mastication and de- 

 glutition. Some gasteropoda (Buccinum Murex Valuta) are 

 furnished with a singular and powerful organ, the proboscis, 

 which they can protrude at pleasure to a considerable dis- 

 tance from the mouth. In the Buccinum (whelk) it is in the 

 form of a hollow tube, surrounded by muscular fibres ; on 

 laying open this sheath we find a bifid cartilaginous tongue, 

 provided with sharp, silicious recurved teeth, and sending out 

 two long processes behind, into which numerous powerful 

 muscles are inserted ; on the right side of the tongue is the 

 opening of the esophagus. The proboscis, in a state of re- 

 pose, is lodged in a distinct cavity, into which it is retracted 

 by numerous longitudinal muscles, having a close analogy in 

 their arrangement with the fleshy columns in the heart of the 

 mammalia. At the point where the esophagus diverges from 

 the proboscis, in Paludina vivipara (fig. 35), it is surrounded 

 vvo salivary glands, which insert their ducts at this part ; 

 N glands are always considerably developed in this class; 



