166 Conchology. 



experiments will lead to the discovery of the cause of the one, 

 and will serve to unfold the other. 



This remarkable variety of color is in no shell more remarkable 

 than in the Helix nemoralis. The ground of this shell is white, 

 citron, or yellow, or a compound of different shades of these col- 

 ors. Different colored rays are traced on this ground, turning 

 spirally with the shell; in some they are black, in others brown, 

 and sometimes reddish. The breadth of each of these rays grad- 

 ually increases as they approach to the opening of the shell. It 

 even sometimes happens, that two of these bands are so much 

 extended in breadth, that they meet together and form one. Some 

 individuals have five or six of these bands, while others have 

 three or four, and even two, and sometimes only one. Others 

 again have none at all, although of the same species; and among 

 the individuals which are marked with colored bands, they are not 

 always of the same breadth in the same parts of the shell; from 

 which it appears, that no certain specific characters can be de- 

 rived from the color, since it is subject to so much variety. Ac- 

 cording to Reaumur, the viscid and earthy matter of which the 

 shell is composed, is secreted from the surface of the animal's 

 body; but in certain places of the surface, particles which pro- 

 duce a different color are separated; and whether this depends on 

 a peculiar organization of those places, or on the form of the par- 

 ticles themselves, it appears that these particles, either of a dif- 

 ferent nature, or of a different figure, by uniting, form bodies 

 which reflect different rays of light; that is to say, form parts of 

 the shell of different colors. 



This seems to be a necessary consequence of the mode in 

 which the growth of shells is accomplished. The whole exter- 

 nal layer of the shell is formed by the neck of the animal, because 

 it is that part which is nearest to the head, and consequently as 

 the animal increases in size, that part ceases to be covered with 

 the old shell. It therefore depends on this part of the animal to 

 extend the shell, and for this purpose it is sufiicient that the neck 

 be furnished with glands for secreting the different fluids, to form 

 a shell of different colors. If, for instance, there are two or 

 three glandular bodies which secrete brown or blackish particles, 

 and that these glandular bodies are disposed in a parallel direction 

 to each other, while the glands on the rest of the surface only se- 

 crete particles of matter which reflect the light of a citron color, 

 the shell formed by these bodies will have a citron ground, with 

 black or brown bands, nearly parallel, or which gradually approach 

 to each other, and become larger in the same proportion as the 

 external organs of the animal increase in size. 



