20 



POPULAR CONCHOLOGY. 



of the animal^ and are enlarged in size by the 

 mollusc, as the shell is increased, in order that 

 they may correspond with and close the aperture. 

 They are found attached to the animal before 

 the egg is hatched. In the foregoing figure are 

 delineations of several varieties of opercula. 

 Some are shelly, and others of a horny con- 

 struction. 



The beautiful and varied colours which shells 

 present are produced by colouring matter con- 

 tained in the pores, which exist in the front 

 part only of the mantle, and which matter is 

 made to penetrate the substance of the shell 

 before it becomes hardened: the experiment 

 before mentioned* will serve also to exemplify 

 this. The portion of shell of which the animal 

 has been deprived (and this may be done with- 

 out injury to the snail,) will be reproduced by 

 the action of the mantle, but the colours will 

 be different according to the situation of the 

 part of the shell which has been broken : if the 

 piece be removed and reproduced at the external 

 lip of the shell, where the front part of the 

 mantle lies, the natural colours will appear in 

 * See page 16. 



