258 CONCHIFERA. 



speedy result. Secondly, it is natural to inquire how 

 is food conveyed into the mouth ? for in an animal, 

 itself fixed and motionless, quite deprived of any 

 means of seizing prey, or even of protruding any 

 part of its body beyond the margins of its abode, it 

 is not easy to imagine by what procedure a due 

 supply of nutriment is procured. 



Wonderful, indeed, is the elaborate mechanism 

 employed to effect the double purpose of renewing 

 the respired fluid, and feeding the helpless in- 

 habitant of these shells. Every filament of the gill- 

 fringe examined under a powerful microscope, is 

 found to be covered with countless cilia, in constant 

 vibration, causing, by their united efforts, powerful 

 and rapid currents, which, sweeping over the entire 

 surface of the gills, hurry towards the mouth what- 

 ever floating animalcules or nutritious particles may 

 be brought within the limits of their action, and thus 

 bring streams of nutritive atoms to the very aperture 

 through which they are conveyed to the stomach, 

 the lips and labial fringes acting as sentinels to admit, 

 or refuse entrance, as the matter supplied be of a 

 wholesome or pernicious character. So energetic, 

 indeed, is the ciliary movement over the entire extent 

 of the branchial organs, that if any portion of the 

 gills be cut off with a pair of scissors, it immediately 

 swims away, and continues to row itself in a given 

 direction, as long as the cilia upon its surface continue 

 their mysterious movements. 



