194 NATURAL THEOLOGY. 



Thus the animal is not only protected by this 

 covering, but, as it grows, the shell is made 

 thicker and stronger by successive layers. 



The reader will not be unwilling that we 

 should stop here to show that, rudely composed 

 as this covering of the oyster seems to be, it not 

 only answers the purpose of protecting the ani- 

 mal, but is shaped with as curious a destination to 

 the vital functions of respiration and obtaining 

 food as any thing we can survey in the higher 

 animals. We cannot walk the streets without 

 noticing that, in the fish-shops, the oysters are 

 laid with their flat sides uppermost ; they would 

 die were it otherwise. The animal breathes and 

 feeds by opening its shell, and thereby receiving 

 a new portion of water into the concavity of its 

 under-shell ; and if it did not thus open its shell, 

 the water could neither be propelled through its 

 bronchiae or respiratory apparatus, nor sifted for 

 its food. It is in this manner that they lie in 

 their native beds : were they on their flat surface, 

 no food could be gathered, as it were, in their 

 cup ; and if exposed by the retreating tide, the 

 opening of the shell Vvould allow the water to 

 escape, and leave them dry — thus depriving them 

 of respiration as well as food.* 



We perceive, then, that the form of the oyster- 



* In conlirmation orfliose remarks, llie iicclogist, when he sees 

 those shells \n beds of tliluviuin, can del ermine wliether the oysters 

 were overwhelmed in their native beds, or were rolled away and 

 scattered as shells merely. 



