INTRODUCTION. 



inattention, we must endeavour to remedy them in 

 the best manner of which we may be capable. 



In the formation and increase of a shell, a very 

 curious process is developed, which we are in- 

 formed, according to the result of much accurate in- 

 vestigation, is the gradual accretion of calcareous 

 matter to the internal surface, from glands situated 

 on the body of the animal, and also to the external 

 margin or superficies, by the action of protruded 

 limbs, or flaps, furnished likewise with glandular se- 

 cretions fitted for the enlargement of the shell . But 

 wliat will appear perhaps still more extraordinary 

 than this gradual method of gaining additional 

 space in proportion to its own growth, is the man- 

 ner in which the tenant, an unsightly slug, paints 

 those beautiful tints and characters which often 

 decorate the walls of his habitation . For this pur- 

 pose, the neck is covered with pores replete with 

 colouring matter, bearing the tones and even the 

 tracing which are afterwards to be deposited on 

 the entrance of the shell, and by degrees to assume 

 the elegant and regular forms and hues which ren- 

 der so many species highly estimable. The elc- 



