Teredo navalis.
Perhaps we may say, with propriety, that this is the only species of the shell-bearing tribes that is decidedly injurious to mankind. The animal of the Teredo is a long worm-shaped creature, dwelling in a tube of a shelly substance, which it forms for itself in its progress through the wood; the small pointed shell-like pieces, to the right in the engraving, form the jaws of the animal. With the assistance of these it cuts its way into the timber, and, at the same time, lines the excavation it is making with a shelly substance, which is gradually formed into a tube, the animal occupying that part which is most deeply sunken in the timber; in directing its course it generally excavates in the direction of the grain of the wood, but in some instances it crosses this grain.
In Holland a great part of the country is below the level of high water, and, to prevent the irruption of the sea, immense dykes have been formed along the coast; these are framed, on the sea-side, of large masses of sand, while to the landward they are strengthened by means of strong piles driven into the ground and wattled together. These piles were once discovered pierced in all directions by this destructive worm, to such an extent as to endanger their safety, and had it not been for a timely discovery of the mischief, immense tracts of country would have been laid under water, and irretrievably lost.
CLASS CIRRHIPEDA.
The Cirrhipeds are well known under the names of Barnacles and Acorn-shells, being found attached to rocks, ships’ bottoms, and pieces of timber which have been under the water for a length of time. They also at times fix themselves on the shells of the larger Mollusca, and on the backs of whales, tortoises, &c. These creatures, from their singular formation, have often proved a stumbling-block in the way of the systematic naturalist, who, from their anomalous characters, was unable to refer them to any part of his system; and although their true nature, which has more recently been discovered by a British naturalist, was partially suspected by Lamarck, (without, however, any definite idea on the subject,) we have still placed them immediately after the Conchifera, although, as we shall presently show, they ought more properly to be ranged with the Crustacea, that is, the crab and lobster tribes, and in future systems this no doubt will be the case.
After noticing their resemblance in many respects to the Crustacea, Lamarck thus expresses himself. “In fact, when I established the class of Crustacea, I formed the first order of this class, (the Cirrhipeds,) under the name of sightless Crustacea, but a few years afterwards I separated them and placed them at the end of the Mollusca, but this was no better. If, for example, we consider those characters which furnish their most important organs, we shall find that the Cirrhipeds, without any doubt, most nearly resemble the Crustacea, for they have the same system of nerves, they have jaws analogous to those of the Crustacea, and their tentacula resemble the antennæ of the shrimps.” To prove that they really were Crustacea, was a task that devolved upon a British naturalist, I. V. Thomson, Esq., a surgeon in his Majesty’s forces. The manner in which this discovery took place, we shall notice further on.
The Cirrhipeds have obtained their name from the hairy feelers, or tentacula, with which they are provided; the name Cirrhipeda being derived from two Latin words,—cirrhus, hair, and pes, the foot; these appendages, being figuratively called feet, although they have, in reality, but little relation to that organ of motion.