CLAMS, MUSSELS, AND OYSTERS. 



47 



By referring to the accompanying figures, these parts 

 may be readily made out : 



FIG. 46. OYSTER ATTACHED BY LEFT VALVE TO A STONE. 



h 



FIG. 47. OYSTEE WITH THE LEFT VALVE REMOVED. h, Heart; Z, Ligament; m, Position 



of Mouth. 



46. The pupil will now recall some characters in common 

 between the snails, and the mussels, clams, and oysters, thus 

 far studied in these lessons, namely : they all have the body 

 protected by a limy shell (except the slug), this shell either 

 composed of one piece, as in the snails, or of two pieces or 



