356 THE SHIP-WORM. 
One species belonging to this family, the Gastrochena modiolina, has been known to 
drive its burrow fairly through some oyster-shells into the ground below, and then to make a 
permanent home by cementing all kinds of materials into a flask-like case and fixing its neck 
into the perforated oyster-shell. | 
TuE very curious and common shells, popularly called Propocks, are found in profusion 
along the sea-coast. 
The common Piddock may be found in vast numbers in every sea-covered chalk rock, into 
which it has the gift of penetrating, so as to protect itself from almost every foe. 
Every one is familiar with the beautiful white shell of the Piddock, crossed by a series of 
elegantly curved projections, something like the teeth of a file. According to some writers, it 
is by means of these projections that the creature is able to burrow into the rock ; and the 
possibility of such a feat has been proved by the simplest possible means, namely, by taking a 
Piddock into the hand and boring a similar hole with it. Myr. Robertson, who kept these 
creatures alive in their chalky burrows, devoted much time to watching them, and finds that 
during the process of burrowing they make a half turn to the right, and then back to the left, 
never turning completely round, and, in fact, employing much the same kind of movement as 
is used by a carpenter when boring a hole with a bradawl. 
Mr. Woodward remarks very justly, that ‘‘ the condition of the Pholades is always related 
to the nature of the material in which they are found burrowing ; in soft sea-beds they attain 
the largest size and greatest perfection, whilst in hard and especially gritty rock, they are 
dwarfed in size, and all prominent points and ridges appear worn by friction. No notice is 
taken of the hypothesis which ascribes the perforation of rocks, ete., to ciliary action, because, 
in fact, there is no current between the shell, or siphon, and the wall of the tube.’? As soon 
as the animal has completely buried itself it ceases to ney and only projects the ends 
of the siphon from the aperture of the tunnel. 
Some species of Piddock are eaten, Pholas costata, one of His South American species 
being a good example. In Europe it is seldom used, except for bait, its fine white foot, which 
looks, when fresh, as if cut out of ice, answering that purpose admirably, its glittering white- 
ness serving to attract the attention of the fish, and its toughness causing it to adhere strongly 
to the hook. 
Several other genera are worthy of notice, among which the Martesia is, perhaps, the most 
curious, shells belonging to this genus having been found in cakes of wax floating on the 
waves off the Cuban coast, and others in masses of resin on the shores of Australia. The 
PapER PHOLAS is another species of this interesting genus. 
Family Petricolide embraces certain clam-like shells that, as the name imports, live in 
stone. Our American species bores into wood, or more commonly it is found in the hard bottom, 
exposed between tide-waters. The shell is a chalky-white, and is long and considerably ridged. 
The celebrated Date-clam is much the same shape, but has a beautiful chestnut epidermis. 
In the Ship-worm we have an example of a creature, which, though useful enough in 
many ways, and doing good service in transmuting dead and decaying substances into living 
forms, is yet the dread of mariners and the terror of pier-builders. 
The Surp-worm derives its name from its depredations on the bottoms of ships and all 
submerged wooden structures. It is found in most seas, and works fearful damage by eating 
into piles, planks, or even loose wood that lies tossing about in the ocean. I have now before 
me a portion of a pier which is so honeycombed by this terrible creature that it can be crushed 
between the hands as if it were paper, and in many places the wood is not thicker than 
ordinary foolscap. This piece was broken off by a steamer which accidentally ran against it ; 
and so completely is it tunnelled, that although it measures seven inches in length and about 
eleven in circumference, its weight is under four ounces, a considerable portion of even that 
weight being due to the shelly tubes of the destroyers. 
IT have also a block of oak, where the Ship-worm has been nearly, though not quite so 
destructive as in the former instance. This specimen is notable, as giving an example of a 
