MOLLUSCOUS TYPE OP STRUCTURE. 



71 



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

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



V 



FIG. 30. ANATOMY OF THE OYSTKR. 



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, muscle of the shell ; br, gills ; 6, mouth ; 

 t, tentacula, or prolonged lips ; /, liver ; t, 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- 



F'fj. 31. LYMKSUB STAQNALIS, OR WATER SXAIL. loped ; and we 



find in some, that 

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



