INTRODUCTION. XIX 



jecture respecting the variegated snail, (and what 

 is said of that will apply to every other) ; if we 

 could perceive nothing similar to the filtres men- 

 tioned by Reaumur, still the theory would furnish 

 so probable an explanation of the variety of co- 

 lours in shells, as to leave us well satisfied with the 

 conception. But fortunately they discover them- 

 selves, and add so strong a degree of evidence to 

 Reaumur's reasoning, that the matter is placed 

 beyond a doubt. The body of the variegated 

 helix, when deprived of its shell, appears of a white 

 colour, except the collar and the parts closely con- 

 nected with it, where we perceive a yellowish tint, 

 and a number of black, or brown streaks, equal to 

 the bands on the shell. Here we come imme- 

 diately at the secret ; the interior of the collar is 

 the laboratory where the colours are prepared ; the 

 surface is the palette, from which the painter lays 

 them on as his work proceeds. Thus the indivi- 

 duals that have one black ray on the shell, have 

 but one black spot on the collar ; those which have 

 four black bands on the shell, have also four cor- 

 responding marks on the collar, and so on with the 

 rest. These rays are placed immediately under 

 those of the shell ; they begin at about the twelfth 

 part of an inch from the extremity of the collar, 

 which is, itself, commonly edged with black all 

 round, and therefore we for the most part find the 

 lip of the shell of that colour. 



