feet are unjointed, and furnished along their inner aspects with a series of cups, which the animal can affix to foreign bodies, on the principle of a cupping-glass.

The PTEROPODS are free Mollusca, which have no feet to arrest their prey, nor foot to creep on; but they float constantly in the water, sustained and moved by means of a pair of fins, which are placed at the sides of the mouth in some of them, and of the neck in others. With their habit of floating near the surface, you will naturally conjecture that a heavy shell is incompatible, and you are right: the shell is always light, thin, and transparent; and even its form is so anomalous, that a Conchologist soon learns to distinguish them, although he may never have seen the living inhabitant.

But the great majority of the cephalous Mollusca creep on the belly, by means of a flat muscular disk, and hence they are named GASTEROPODS. The slug, the snail, the whelk, periwinkle, and limpet, are familiar examples of this class. On tropical shores its representatives are found in the cowries, cones, and volutes, the pride of all collectors, and in the rosy cheeked conchs or spinous rock-shells brought home from foreign climes by the sailor-boy, to become the favourite ornament of the chimney-piece of our English parlours.

The acephalous Mollusca form two classes: one the bivalvular or CONCHIFERA, known by its shell, which is always formed of two pieces or valves, shutting against each other and enclosing the animal, as the oyster and cockle; the other class affords no familiar illustrations, for it is composed of creatures which are neglected and unnamed by the vulgar. They have been called TUNICATED Mollusca, for they are in no instance covered with a shell, but merely with a leathery or soft carnous tunic, in which there are two circular apertures, one for the admission of water and food into the interior, and one by which the effete and excrementitious parts are expelled. Cuvier enumerates two other classes of this section: the BRACHIOPODS, which are properly a subclass of conchiferous Mollusca, furnished with a pair of fleshy ciliated arms, capable of being protruded beyond the circumference of the shell, and made subservient apparently to respiration as well as the attraction of food: the other class is the CIRRHOPODS, in which the famous Barnacles and Acornshells are included; but as recent discoveries have proved that these belong properly to annulose or crustaceous animals, we must exclude them from our Molluscan assemblage.

Such then are the names and distinctions of the primary tribes of the class of animals whose history I have undertaken to give you, and which it seemed necessary you should know

before we could proceed further. I enter on the task willingly, and owe you indeed thanks for having imposed it on me, since it is very congenial to my taste, and will supply pleasant occupation for hours, which might otherwise have been wasted in idleness or ennui. If I succeed in communicating to you a portion of my own enthusiasm, I feel assured you will not repent having been brought into this way of study. Several years have passed away since I entered upon it, and each succeeding year the path has become pleasanter and more thickly strewed with flowers; and your experience, trust me, will be correspondent. The alphabet undoubtedly must be first acquired, and alphabets are irksome; what others have done must be learned, and in this we have little other enjoyment than what every one is conscious of while adding to his stores of knowledge; but when you are thus prepared to enter into all the perplexities of synonymes, and all the niceties of systematical arrangement, to balance the pros and cons, and try your skill in untying Gordian knots which others, you fondly deem, have vainly tried to untie before, then begins your real interest and zest and leaving even these small points behind, you may go onwards to trace the paths which Lister and Cuvier loved to tread-to examine the living animals in their haunts-unravel, with the knife and the glass, the perplexed structure which supports their life and regulates their functions and their habits.

"By swift degrees the love of nature works,
And warms the bosom,"-

Enthusiasm grows apace, and now, strong enough, you are urged to explore untrodden paths where, amidst the new structures and unveiled proofs of your Creator's wisdom which disclose themselves at every step, you lose yourself in rapture and praise!

* "Scandenti circa ima labor est: cæterum quantum processeris, mollietur clivus, et lætius solum. Et, si hæc quoque jam lenius supina perseverantibus studiis evaseris, inde fructus illaborati, offerunt sese, et omnia sponte proveniunt: quæ tamen, quotidie nisi decerpantur, arescunt.”— Quinctilian, Instit. Orat. xii. 10.

9

LETTER II.

THE MOLLUSCA CONSIDERED AS HURTFUL ANIMALS.

It is natural to conclude, that if the snail and oyster fairly represent the class, man can have nothing to fear from animals of such limited faculties and proverbial hebetude; and while I willingly admit that they have no claim to any bad pre-eminence among his enemies, there are still some noxious species of celebrity among them, whose evil works may occupy our attention in this letter.

Of the marine tribes, the Shipworm (Fig. 1, b), is the only one which has attracted much attention; but the devastation this worm-like Mollusk commits, is sufficiently extensive to have earned for it a hateful notoriety, and justifies the strong language of Linnæus, when he styles it the "calamitas navium. It has been gifted with the power of boring into wood, and while following this instinct, and working out the plans of Providence in removing wrecks and obstructions which have been carried to the ocean, ships, piers, and bulwarks are equally obnoxious to it, and by drilling them in every direction, they soon become unable to resist the violence of the waves, and are washed away. The amount of the damage which the Teredo thus inflicts on marine property is difficult to calculate; that it is very considerable is proved by the complaints made of the mollusk in almost all

seas, and the numerous expensive methods which have been adopted to avert its attacks. There is in the Indian seas, says an anonymous traveller, "a kind of small worms that fasten themselves to the timber of the ships, and so pierce them, that they take water everywhere; or, if they do not altogether pierce them through, they so weaken the wood, that it is almost impossible to repair them. To preserve the ships," he continues, "some have employed deal, hair, and lime, &c. and therewith lined their ships; but, besides that this does not altogether affright the worms, it retards much the ship's course. The Portugals scorch their ships, insomuch that in the quick works there is made a coaly crust of about an inch thick. But as this is dangerous, it happening not seldom, that the whole vessel is burnt; so the reason why worms eat not thorow Portugal ships is conceived to be the exceeding hardness of the timber employed by them."* In the West the Teredo is equally active, as the observations of Sir Hans Sloane and Dr. Browne prove.† Our early navigators were frequently thwarted or controlled in their bold enterprises by their ships being rendered, by its means, unsafe or useless; and as our commerce enlarged, the evil was so severely felt that it led to the plan of sheathing the bottoms of ships with lead and copper, for which important discovery an Act of Parliament was passed to secure to Sir Philip Howard and Major Watson the sole use and profits which might accrue from it. From the tropical seas the Teredines were commonly believed to have been introduced into those of Europe, somewhat less than two centuries ago; but as there is more than sufficient evidence to prove that certain species are truly indigenous, ‡ the hope vanishes of ever seeing them extirpated by a winter severer than usual, or by a continued temperature inimical to their constitution, as might have happened had they been colonists from the tropics; for the Teredo almost always resides near the surface, and often in situations which are left dry during the ebb, where it is

*Phil. Trans. an. 1666, p. 190.

+ Hist. of Jamaica, p. 395. Dr. Browne has erroneously figured a species of Nereis for the "ship-worm."

In some parts of the London clay, branches and stems of trees, penetrated by the Teredo navalis are found."—Bakewell's Geology, p. 325. At Belfast, it has been found buried in blue clay twelve feet beneath the surface, where it must have been deposited centuries before Europe enjoyed any commerce with either the East or West.-Edin. New Phil. Journ. xviii. 126. For correct descriptions and figures of our native species, the reader is referred to the "British Mollusca" of Forbes and Hanley, i. p. 66-89. The authors have given an interesting sketch of the Teredo's misdeeds as an introduction to their account of the species.

necessarily subjected to the atmospherical changes. Its destructive operations in European seas are not therefore weakened by a less genial locality. In the years 1731 and 1732, the United Provinces were under a dreadful alarm;* for it was discovered that these Mollusks had made such depredations on the piles which support the banks of Zealand and Friesland, as to threaten them with total destruction, and to reclaim from man what he had with unexampled labour wrested from the ocean. A few years after they fortunately abandoned the dikes; but fearful of the return of an enemy more powerful than the Grand Turk even, who boasted that he would exterminate them with a host armed with spades and shovels, the Dutch offered a reward of value to any one who should discover a remedy to ward off their attacks, and ointments, varnishes, and poisonous liquors were recommended by the hundreds. The exact amount of the damage done at this visitation, which Sellius, unable to discover any natural cause for it, says was sent by the Deity to punish the growing pride of the Hollanders, I have not been able to ascertain. Writers in general speak of it as " very great; and Dr. Job Baster mentions the Teredo as an animal "which has done so many millions damage to these countries."+-In our own country it has done, and continues to do, extensive mischief. The soundest and hardest oak cannot resist these noxious creatures; but, in the course of four or five years, they will so drill it as to render its removal necessary, as has repeatedly happened in the dock-yard of Plymouth. To preserve the timbers used there, and exposed to them, the plan now adopted is to cover the parts under water with short broad-headed nails, which, in salt water, soon invests the whole with a strong coating of rust impenetrable by their augers. The plan appears to have proved effectual, for, in the harbours of Plymouth and Falmouth, where the Teredo was once abundant, it is now rare or not to be found; § but

* "Quantum nobis injicere terrorem valuit, quum primum nostros nefario ausu muros conscenderet, exilis bestiola! quanta fuit omnium, quamque universalis consternatio! quantus pavor! quem nec homo homini, qui sibi maxime alias ab invicem timent, incutere similem, nec armatissimi hostium imminentes exercitus excitare majorem quirent. In planctus et lamentationes, ut sunt commune hominum in calamitatibus refugium, effusis plurimis; in investigandis remediis, salubriore consilio, toti occupabantur alíi.' Sellius. Also Baster, Opusc. Suhs. ii. 67.

+ Phil. Trans. abridg. viii. 379.

Montagu Test. Brit. 530. This author suggests a coating of pounded flint or glass, laid on the timber with a firm cement, as probably an efficient remedy.-Ibid. 561. The bitter juice of the great American aloe, mixed with pitch, is said to be a preservative.-Lin. Corresp. i. 133.

§ Osler in Phil. Trans. an. 1826. part iii. 358.-Dr. Paris, however, on