4 CONCHOLOGIST’S COMPANION. 
The animals which inhabit these stratified shells, 
increase them every year by a stratum of carbonate of 
lime, secured by a new membrane; and thus the 
age and growth of the animal may be readily ascer- 
tained. 
The two substances of which shells are composed, 
may be separated from each other by an easy chemi- 
cal experiment, in the gentle operation of which they 
become exhibited distinctly to the view, without any 
material alteration from the nature of the solvent 
employed for that purpose. Thus, if a sufficient 
quantity of nitric acid, considerably diluted either 
with water or spirits of wine, is poured upon a shell 
or fragment of one, contained in a glass vessel, it will 
soon exhibit a soft floating substance, constituting 
the animal part of the shell, and consisting of 
innumerable membranes resembling a net. These 
membranes retain the exact figure of the shell, and 
afford a beautiful and popular object for the micro- 
scope. They exhibit satisfactory proofs that this 
membranaceous substance is, in fact, an appendage to 
the body of the animal, or rather a continuation of 
the tendinous fibres, that form the ligaments, by 
means of which it is fixed to the shell. They also 
prove that the shell itself owes its hardness to the 
earthy particles perspired through the vessels of the 
animal, which gradually incrust the meshes formed 
