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One observation leads to another. From the pearl we may get to the operculum. Some 

 readers may ask, what is this ? It seems to be a protection to the inhabitants of some univalve 

 shells, why to some kinds only I cannot explain, neither can I explain, whilst in some it is 

 merely of a horny or matted hairy description, in others it is of the same apparent composition 

 of the shell as is the pearl ; but instead of beimg like it, an extraordinary production caused 

 by disease, it is part of the ordinary necessity for the animal inhabiting the peculiar kind of 

 shell, so that probably when it is attacked by some deadly enemy, it withdraws itself into its 

 shell, and closes its impenetrable barrier behind it and is safe. But how and why one species 

 has the horny operculum, like our common silver shell, and some of the foreign species have 

 the formidable shelly protection, I know not. The larger land snails have no operculum, but 

 when they hybernate, a hard substance shuts them in for a season, no doubt as a protection 

 from some enemy during the long time they are at rest, and during it only as it is a fixture 

 and immovable, and entirely unlike the ordinary operculum which is constantly attached to the 

 living animal. The horny operculum seems to be of a similar composition to the epidermis on the 

 outsides of many kinds of shells, which hides much of their colour; how it grows is a mystery 

 on the hard shell, and really it has the appearance often ol a kind of vegetable growth ; why 

 some shells have it, and others, apparently somewhat similar, are without it, who can tell ? 



It may be sometimes as a protection from some enemy, as it probably assimilates the shell 

 to the ground; but with what kind of eyes do the inhabitants of the deep look upon their food, 

 or by what method are they guided to it, is a subject for contemplation. Do they distinguish 

 colour or shape, or do they often find it by the smell? Perhaps each is possessed of some 

 sense we know nothing of. 



H 



