302 ANIMAL SKETCHES. CHAI>. 



action of an elastic cushion near the hinge, which when the 

 shell is closed is in a state of compression, but which when 

 the oyster dies and the muscle relaxes, or when the muscle 

 is severed, serves by its elasticity to force the shell agape. 



When the oyster has been opened and the valve of the 

 shell has been removed, then unless the force of habit 

 prove too strong and the molluskbe incontinently swallowed, 

 for even a penny oyster hath its charms and its tempta- 

 tions then, I say, the following points about its structure 

 may be readily made out, and all the more readily if it be 

 placed in a soup-plate of water. In the first place the 

 mollusk will perhaps not occupy the whole surface of the 

 shell. This is due to severe muscular spasms consequent 

 to the shock its system has recently undergone. But in 

 the living state, closely applied to the whole of the interior 

 of the two valves, are the two lobes of the mantle, which 

 are given off from the body as thin layers of fleshy sub- 

 stance, the edges of which are thickened and bear a coarse 

 reddish-brown or dusky fringe. In the contracted mollusk, 

 as it lies in the shell before us, the mantle-lobes may be 

 recognized by their fringed edges. 



Our next task is to find out which is head and which is 

 tail in our oyster or rather, since it hath neither head nor 

 tail, its top and bottom, its front and rear. The hinge is 

 at the top, the valves of the shell on either side. The 

 oyster usually rests on its larger and more convex left 

 valve, so that, like a flounder, it lies on its side. The 

 hinder margin of the shell is usually somewhat straighter 

 than its anterior edge. This and the shape of the shell 

 will generally serve to distinguish right from left and front 

 from back. But the front of the contained mollusk itself 

 may readily be distinguished from its rear by the sickle- 

 shaped gills, four in number, which curve round in front of 

 the body, and lie between the mantle-lobes. The gills are 



