68 STRUCTURE OF THE OYSTER. 



size ; and the other viscera. It has been said, that 

 the gills are the aerating organs, but they also serve 

 another important purpose. It must strike every one 

 who sees an oyster, and considers how inertly it lies, 

 attached to its native rock, or to the bed whence it has 

 been taken, that some special means of procuring food 

 must be possessed, since the animal has neither the 

 power of perceiving nor of following its prey ; and 

 herein the branchiae fulfil a secondary but essential 

 office. The water which traverses these branchiae con- 

 tains abundance of animalcules, on which the animal 

 subsists ; and by the action of minute cilia, to be seen 

 only by means of a microscope, with which the filaments 

 of the branchiae are thickly covered, the water is kept 

 constantly agitated, the element in immediate contact 

 with the branchial surfaces being thus perpetually re- 

 newed, and as necessarily so as is the air we breathe. 

 Let us mark how wise and beautiful a provision is made 

 for the creature's good : the action of these cilia pro- 

 duces strong and rapid currents, the course of which is 

 directed to the mouth, and with them are carried the 

 nutritious particles on which the mollusk lives. The 

 lips of the mouth are endowed with an amazing sense, 

 which rules them as to what particles to receive, and 

 what to reject ; and thus a constant supply of food is 



