12 



POPULAR CONCHOLOGY. 



dimensions by the aid of its mantle. This por- 

 tion of the body of the animal, as before men- 

 tioned, has the power of exuding a liquid 

 matter, which, on exposure to the air or water, 

 becomes shell, and the mollusc makes the ad- 

 dition to its original habitation by protruding 

 the mantle beyond the edge, and suffering it in 

 that manner to remain exposed : in a short time 

 it is found to be covered with a fluid which has 

 been secreted, and this gradually and slowly 

 assumes consistence, fresh layers being added 

 within, each projecting a little farther at the 

 edge, and thus the new formation becomes si- 

 milar to the shell already in existence. This 

 operation is repeated at intervals, as the animal 

 increases, so that by this beautiful contrivance 

 the shell and its inhabitant are always adapted 

 to each other, and preserve their relative pro- 

 portions. 



As the new portion of shell is always similar 

 in shape, and, in fact, takes its form from that 

 part of the mantle which is pushed out, it is 

 evident that the conformation of every shell 

 will depend upon the manner in which the 

 Mollusc protrudes its mantle, and that it will 



