INTRODUCTION. 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 ele- 



