A fragment of rock riddled by the Pholas is a much more pleasing sight than can be witnessed at the sea-shore in connection with that animal under usual circumstances. For this reason: When visiting the habitat of the boring bivalves, a host of small circular holes are sometimes seen; at other times the surface of the same portion of the beach appears comparatively sound, and it is only by striking a smart blow with a hammer upon the ground, that we render scores of orifices instantly observable in all directions, from each of which is thrown a small jet of water. This phenomenon is caused by the Pholades in alarm retracting their siphons, which had hitherto filled the entire extent of the tunnels. At such a locality, if a piece of rock be excavated, various specimens of these boring molluscs, shrunk to their smallest possible size, will be discovered at the base of the cavities, which are invariably of a conical form, tapered at the top, and gradually enlarging as they descend. It must be evident, then, that neither the likeness of the animal, nor the formation of its singular dwelling-place, can be seen by the casual wanderer along the sea-shore. It will also be apparent to the intelligent reader, that when once the Pholas is located in a certain spot, he becomes a tenant for life; for never by any chance whatever, can the poor miner leave his rocky habitation by his own unaided exertions, even were he so inclined. As he grows older and increases in size, nature teaches the animal to enlarge his habitation in a proportionate and suitable manner. During the period of the boring process, the orifice becomes clogged above the shell with the _debris_ of the rock, and this, if allowed to accumulate would speedily asphyxiate the animal. To get rid of such an unpleasant obstruction, the Pholas retracts, and closes the end of its siphons, then suddenly extends the 'double barrelled' tube to its full length, until it reaches the entrance of the tunnel. This movement often repeated, causes portions of the pulverized stone to be forced outwards at each operation. It is interesting to watch the curious manner in which the end of the principal siphon is alternately closed and spread out when it reaches the water, like a man inspiring heavily after any unusual exertion; it is then made again to descend, and renew its task, as above described. In extracting that portion of the _debris_ which is deposited at the _base_ of the cavity, below the body of the industrious miner, a different plan is adopted. Wherever a Pholas is at its labours, there are always deposited within a circumference of several inches round the tunnel, myriads of short thin threads, which are squirted out from the smaller siphon.