30 THE OYSTER. 



PLATE I. 



FIGURE i. The left side of an oyster lying in one 

 shell, with the other shell removed. The mantle has 

 been turned back a little, to show its fringe of dark-col- 

 ored tentacles, and in order to expose the gills. The 

 part of the mantle which is turned back in this figure 

 marks the place where the current of water flows in to 

 the gills. 



FIGURE 2. An oyster in the left shell, with the right 

 shell and right fold of the mantle removed, to show the 

 gills and the body of the oyster. 



a is the hinge, b the edge of the mantle, c is the 

 muscle, d is the pericardium, / is the hinge ligament, 

 g the gills, h the lips. 



