MOLLUSCOUS TYPE OF STRUCTURE. 



71 



This is the case with all the animals inhabiting bivalve shells ; 

 although some of them have a fleshy tongue-like organ, termed 



c m 



FIG. 30. ANATOMY OF THE OYSTBR. 



v, one of the valves of the shell ; v', its hinge ; m, one of the lobes of the mantle ; 

 m', a portion-of the other lobe folded back ; c, muscles of the shell ; br, gills ; b, mouth ; 

 t, tentacula, or prolonged lips ; /, liver ; i, intestine ; a, anus ; co, heart 



the foot, by which they can give motion to their bodies. But 

 among the Mollusks inhabiting univalve shells, and others which 



are allied to them 

 but possess no shell, 

 we find the mouth 

 situated on a pro- 

 jecting part, which 

 also bears the va- 

 rious organs of spe- 

 cial sense, sight, 

 smell, hearing, and 

 taste, more or 

 less fully deve- 

 loped ; and we 

 find, in some, that 

 the powers of motion are greater, so that they are enabled to 



FIG. 31 LYMNJEUS STAGNALIS. 



