INTRODUCTORY CHAPTER. 



15 



which exists in the front part only of the mantle, and which 

 matter is made to penetrate the substance of the shell before 

 it becomes hardened : the experiment before mentioned* 

 will serve also to exemplify this. The portion of shell of 

 which the animal has been deprived (and this may be done 

 without injury to the Mollusc) will be reproduced by the 

 action of the mantle, but the colours will be different ac- 

 cording to the situation of the part of the shell which has 

 been broken : if the piece be removed and reproduced at 

 the external lip of the shell, where the front part of the 

 mantle lies, the natural colours will appear in the new 

 piece ; but if the fracture has been made at a distance 

 from the aperture, and in the body of the shell, a new 

 portion will indeed be made by that part of the mantle 

 which has been laid bare, but it will be white or nearly 

 colourless ; thus proving, that, although every part of the 

 mantle can produce shell, the external edge alone can infuse 

 colour into it. The brilliancy of the colours observed in 

 shells is exceedingly influenced by the degree of health, 

 and by the food, light, and heat which the mollusc has had 

 the power of enjoying. Those which inhabit tropical 

 countries have often a very great degree of brilliancy and 

 beauty ; whilst others, which are less favoured by climate, 

 and, still more remarkably, those which remain all their 

 lives enclosed in wood, chalk, &c, have little or no colour. 

 It is observable, also, in a similar manner, that a great 

 difference frequently exists in the size of mature shells of 

 the same species, particularly in such as have the strongly 

 marked lip, or other final appendage : this may be ac- 

 counted for by the strength or weakness of constitution 

 existing in different individuals, influenced undoubtedly by 

 favourable or unfavourable situations, and abundance or 



See page 1 1 . 



