356 THE SHIP-WORM. 



One species belonging to this family, the GastrocJicena 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 ease and fixing its neck 

 into the perforated oyster-shell. 



The very curious and common shells, popularly called Piddocks, 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 tile. 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 lias been proved by the simplest possible means, namely, by taking a 

 Piddock into the hand and boring a similar hole with it. Mr. 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, etc, 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 burrow, and only projects the ends 

 of the siphon from the aperture of the tunnel. 



Some species of Piddock are eaten, Pholas costdta, one of the 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 interestin.c genus. 



Family Petricolidce embraces certain clam-like shells that, as the name imports, live in 

 stone. Our American species bores into wood, or more commonly if 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 ^ame 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 Ship-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 ii 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. 



I 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 



