18 Red Sea Shells. 



and classified by its colours, its whorls, or its hinges, without 

 regard to the creature that tenants it? or is it something more than 

 this ; possibly as much a part of the animal that is attached to it 

 as the vertebrae of our spines are part of ourselves ; no dead 

 matter, but a living substance ? Such indeed is the fact, and one 

 of the main differences between the baby mollusc and the baby 

 man is this, that while the bony structure of the human being is 

 gradually developed within the soft fleshy integument that hides 

 it from our view, to serve, so to speak, as its framework and sup- 

 port ; the mantle (as it is technically called) of the mollusc, which 

 is a flexible membrane enveloping its body, secretes by degrees a 

 substance harder than our bones, to form not in this case a frame- 

 work, but an external defence of the pulp, which we call its shell. 

 Some molluscs indeed there are, the cephalopods or cuttlefishes, 

 about whose peculiarities I hear the Society is already promised a 

 paper, that have no external shell, but a kind of bone which lies 

 loosely in the mantle, but the shells of most molluscs are thrown 

 off externally. The mantle in the univalves generally takes the 

 form of a sac, with an opening in front from which the head and 

 limbs of the animal project. In the bivalves it is divided into two 

 separate lobes, which lap over the two valves. Now to return to 

 our cowrie, which, though a univalve, has a two-lobed mantle; we 

 can understand how each layer of the shell, for it consists of many, 

 was once part of that mantle, either in the form of a simple mem- 

 brane, or a tissue of cells ; and that, as new layers of shelly 

 matter were successively thrown off and spread over the old layers ; 

 what was at first but a thin crust became a coat of mail, till at last 

 the points and edges of the young mollusc were rounded into the 

 smooth shining armour of the adult. Nor was this all, for while 

 fresh layers of enamel were being added externally by the over- 

 lapping mantle, the creature kept continually dissolving the internal 

 layers of its shell-wall, as if bent on obliterating all traces of its 

 youth. The pale streak we generally notice on the back of the 

 cowrie indicates the point of junction, or approximate junction of 

 the two lobes of the mantle. Over all is spread the epidermis, 

 which is of animal matter, formed by the margin of the mantle, 

 and upon this the colours of some shells, especially of land shells, 

 depend. Here is a strorab which was once mottled. You see I 

 have removed all vestige of colour by removing the epidermis. 

 But the tints and patterns we admire most are usually confined to 

 the surface beneath the outer coat : and are often noticeable upon 

 the mantle itself, which transfers them to the shell. You may 

 often liberate the most beautiful colours on a common looking 

 trochus by removing the outer layer with spirits of salt ; a little 

 further perseverance with acid and brush, will reveal the pearly 



