144 Conchologi/. 



on the side which is in contact with the animal's body; and nd 

 matter whatever was deposited on the other surface. This ex- 

 periment has been repeated by others, and has been invariably 

 attended with the same result. 



The second experiment made by Reaumur is not less decisive 

 than the first. He took a number 6f snails, and broke the shells, 

 so that he diminished the number of the turns of the spire about one 

 seventh part. Having in this way rendered the shell too small 

 to cover the body entirely, they were nearly in the same situation 

 as when an increase of the animal's body requires an augmentation 

 of the shell. He then took a bit of skin, as in the former ex- 

 periment, sufficiently large to cover the opening of the shell, and 

 introduced one of its edges between the body of the animal and the 

 shell, to the interior surface of which he glued it; after which hav- 

 ing folded back the other extremity of the skin on the external sur- 

 face of the shell, he glued it in like manner, so that the whole 

 external opening was completely covered with the skin. The 

 results were exactly the same as before. The shell grew, the 

 skin remained in its place, and that part of it which was attached 

 to the interior surface, was fixed between the new piece and the 

 old shell, which consequently could not contribute to its formation. 



From these experiments, which may be easily repeated, it ap- 

 pears that the increase of shells is owing to the secretion of an 

 earthy and viscid animal matter which is prepared in the body of 

 the animal, and which is successively formed by layers from the 

 interior part of the shell to the external surface. This formation 

 is determined by the previous enlargement of the animal. The 

 different strata or layers of which shells are composed, can be ea- 

 sily demonstrated by exposing them to the action of fire, and re- 

 moving them before their structure is entirely destroyed. By 

 this process the animal matter is consumed, and the earthy sub- 

 stance remains, exhibiting a laminated structure. The same 

 structure may be demonstrated, as has been already observed, in 

 detailing Mr. Hatchett's experiments, by immersing a shell of the 

 description of mother of pearl in a diluted acid. The earthy mat- 

 ter in this case is dissolved by the acid, and the layers of animal 

 matter which are interposed, resisting the action of the acid, re- 

 main unchanged, and still retain the original figure of the shell. 



It is a necessary consequence of the mode in which the shells 

 of snails are increased, that they cannot enlarge in volume, but 

 by the augmentation of the turns of the spire, and that the length 

 of each turn of the shell already formed, remains always the same: 

 This may be easily put to the test of experiment, by reducing the 

 shell of a snail which has reached its full size, to the same num- 



