Conchology. 143 



and particularly if the fracture is made near the edge of the open- 

 ing, the animal is not supplied with a sufficient quantity of nour- 

 ishment, its volume or bulk is soon diminished; and now finding 

 that what remains of the shell is a complete covering to its dimin- 

 ished body, no excretion takes place for the production of a new 

 portion. In removing snails from a wall to which they had at- 

 tached themselves, for the purpose of observing the progress of 

 the formation of the shell, some days will elapse after they are 

 placed in the box, before the process commences, because the 

 testaceous matter which had been already expended after fixing 

 on the wall, must be fully supplied before any new portion can be 

 again formed. 



This experiment shows clearly, that shells are only enlarged by 

 receiving new additions of matter, after it has been excreted from 

 the body of the animal, and not by intus-susceplion^ or a circula- 

 tion through the body of the shell itself. If this were the case, 

 the prodiiction of new matter to fill up the breach made in the 

 phell, would first appear all round the edge of the opening, and 

 forming a kind of callus, similar to what happens in the reproduc- 

 tion of bony matter in other animals, it would gradually extend till 

 the whole breach is filled up. But, on the contrary, this matter 

 first appears on the body of the animal from which it has exud- 

 ed, and the whole extent of the opening is closed at once by the 

 fluid which has been directly secreted from the surface of the 

 body. Nor can it be supposed that the Hquid has insensibly ex- 

 uded from the shell, and falling on the body of the animal, is 

 there collected in sufficient quantity for the formation of the new 

 piece of shell. This is fully demonstrated by the two following 

 experiments of the same naturalist. 



Reaumur broke several shells of snails, and, having made a very 

 large hole about the middle of the shell, and about midway between 

 its summit and opening, he introduced between the body of the ani- 

 mal and its shell, through the hole, a piece of skin which was ex- 

 tremely fine, but of a very close texture. He glued this skin to the 

 internal surface of the shell, so that it shut up accurately the artifi- 

 cial opening which he had made. It must then be obvious, that if 

 the reproduction of the piece of shell which was removed, depend- 

 ed on the excretion of a fluid from the shell itself, and not on that 

 which proceeds from the surface of the animal's body, the new 

 piece of shell would be formed on the external surface of the piece 

 of skin which was introduced; and it is not possible that it could 

 be formed between the skin and the body of the animal. But the 

 contrary of this has always happened. The new testaceous mat- 

 ter is always deposited on the internal surface of the skin; that is, 



