THE CYPREA. 99 



lusks. They do not, indeed, possess organs of hearing, 

 because they have no internal skeleton ; but they have 

 organs of vision, and of taste. The mouth is furnished 

 with teeth and a tongue ; and it would appear, though 

 no apparatus has been detected, that they are capable 

 of smelling. Most are covered with a shell, the pro- 

 duct of a delicate mantle, and into this shell they have 

 the power of retracting themselves entirely, and some 

 of closing the orifice with a horny, or a calcareous lid, 

 or operculum. To describe the variations of form 

 which the shell assumes in various groups and species, 

 is impossible in a cursory review like the present ; nor, 

 indeed, is it necessary, for every observer must have been 

 impressed with the fact, and have been delighted with 

 the beautiful colouring so often exhibited. All the 

 gasteropoda, however, are not thus furnished with a 

 transportable habitation. In the slug, a little plate, 

 the rudiment of a shell, is embedded in the substance 

 of the mantle, but to which it is not adherent ; and in 

 one group (the nucUbranchia of Cuvier, of which the 

 doris is an example,) not even this is to be found. In 

 the cyprea, or cowrie, belonging to the j^^c^tinihranchiate 

 group, the glossy porcelain-like shell is, at a certain 

 period, enveloped in an ample mantle, which, extend- 

 ing from the aperture^ falls over the shell on both 



