X INTRODUCTION. 



shell, of one spire. The animal, shell and all, is 

 not at that time larger than a split pea ; therefore 

 much remains to be done, before it acquires its full 

 growth and solidity. The inhabitants of univalve 

 shells, such as the snail, periwinkle, whelk, &c. con- 

 stantly enlarge their apartment, by adding fresh 

 accessions of materials to the mouth. The whole 

 body indeed is covered with pores, through which 

 a viscid liquor exudes ; but the part which contri- 

 butes principally to the increase of the shell, is a 

 fleshy collar above the neck. This in the snail is 

 very visible ; and on opening its substance, a glan- 

 dular tissue is seen, of a whitish colour, and studded 

 with little semi-transparent points. These points 

 are noticed by Cuvier, who adds that, upon irritat- 

 ing the snail, it will throw out, from all parts of its 

 collar, a white liquid, visibly formed of calcareous 

 molecules, suspended in a viscous fluid We have 

 here pretty evident marks of design ; a storehouse 

 for the preparation of materials is placed where a 

 storehouse only could have been of use. The rest of the 

 body is confined by shell : the animal, if it increases 

 at all, must increase by the mouth ; and if unpro- 

 vided with the means of enlarging its room by 

 the aperture, it would become a long naked snail, 

 with merely the shell it was born with on its tail. 

 But we have seen what provision nature has made 

 in the snail against nakedness. As the body pro- 

 trudes, the collar secretes, and lime and glue, which 



