INTllODUCTION. 
5 
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 
investigation, is the gradual accretion of calcareous 
matter to the internal surface, from glands situated 
on the body of the animal, and also to the exter- 
nal margin or superficies, by the action of protruded 
limbs, or flaps, furnished likewise with glandular 
secretions fitted for the enlargement of the shell. 
But what will appear perhaps still more extraor- 
dinary than this gradual method of gaining addi- 
tional space in proportion to its own growth, is the 
manner in which the tenant, an unsightly slug, 
paints those beautiful tints and characters which 
often decorate the walls of his habitation. For this 
purpose, 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- 
