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of the one part into the other upon which their mutual action depends. The extent and nature of the motion is determined by the nature of the articulation, which is varied with the nicest skill to answer the purpose intended. In ostraceous worms the only articulation is that of the hinge: in the cancer tribes the tendon is articulated with the crust, whence the wonderful strength and activity of the claws; and it is articulated in a similar manner with the scaly plates of some species of the tortoise. In insects the part received and the part receiving form each a segment of a spheroid ; whence the motion may be either rotatory or lateral, at pleasure. In mammalian animals the lower jaw only has a power of motion; but in birds, serpents, and fishes, the upper jaw in a greater or less degree possesses a similar power.

The motion of serpents is produced, according to Sir Everard Home, by their ribs, which for the most part accompany them, not only as organs of respiration, but from the hind extremity to the neck, and are possessed of a peculiar power of motion by means of peculiar muscles. “ The vertebræ are articulated by ball and socket joints (the ball being formed upon the lower, and the socket on the upper one), and have therefore much more extensive motion than in other animals.” In the draco volans the skeleton of the wings is formed out of ribs which“ are superadded for this purpose, and make no part of the organs of respiration; the ribs in these animals appear to work in succession, like the feet of a caterpillar."

The teeth vary in their form and position almost as much as the bones. Where jaw-bones exist they are usually fixed immoveably in their sockets; but in some animals a few of them are left moveable, and in others the whole. The mus maritimus, or African rat, the largest species of this genus which has hitherto been discovered, and seldom less than a full-sized rabbit, has the singular property of separating at pleasure to a considerable distance the two front teeth of the lower jaw, which are not less than an inch and a quarter long. That elegant and extraordinary creature the kangaroo, which, from the increase that has lately taken place in his Majesty's gardens at Kew, we may soon hope to see naturalized in our own country, is possessed of a similar faculty. And the hollow tusks or poisoning fangs of the rattlesnake, and other deadly serpents, are situated in a peculiar bone on each side of the upper jaw, so articulated with the rest, that the animal can either depress or elevate them at his option. In a quiescent state they are recumbent, with their points directed inwards ; but whenever the animal is irritated he instantly raises them ; and at the moment they inflict a wound, the poison, which lies in a reservoir immediately below, is injected through their tubes by the act of pressure itself.

In the shark and ray genera the whole of the teeth are moveable, and lie imbedded in jaw-cartilages instead of in jaw-bones, and like the fangs of the poisonous serpents are raised or depressed at pleasure. The teeth of the xiphias gladius, or sword-fish, are similarly inserted; while his long swordlike snout is armed externally, and on each side, with a taper row of sharp, strong, pointed spines or hooks, which are sometimes called his teeth, and which give rise to his popular name.

The ant-eater and manis swallow their aliment whole ; and in many animals the jaws themselves perform the office of teeth, at least with the assist

ance of the tongue. In birds this is generally the case, sometimes in insects, · whose jaws are for this purpose serrated or denticulated at the edge, and fre

quently in molluscous worms. The jaws of the triton genus act like the blades of a pair of scissors. The snail and slug have only a single jaw, semilunar in its form, and denticulated : but the mouth of the nereis has several bony pieces. The sea-mouse (aphrodita aculeata) has its teeth, which are four, fixed upon its proboscis, and is of course able to extend and retract them at pleasure ; and the leech has three pointed cartilaginous teeth, which it is able to employ in the same way, and by means of which it draws blood freely. In like manner, though insects cheifly depend upon a serrated jaw, yet many of them are also possessed of very powerful fangs, of which we have a striking instance in the aranea avicularia, or bird-spider, an inhabitant of South America, found among trees, and a devourer of other insects and even small birds. It is of so enormous a size that its fangs are equal to the talons of a hawk; and its eyes, which are eight in number, arranged as a smaller square in the middle of a larger, are capable of being set in the manner of lenses, and used as microscopes.

In many animals, especially the herbivorous, the tongue itself is armed with a serrated apparatus, the papillæ being pointed and recurvated, and enabling them to tear up the grass with much greater facility. In the cat-kind the tongue is covered with sharp and strong prickles, which enable the ani. mal to take a strong hold; and similar processes are met with in the bat and the opossum. In the lamprey and myxine families, the tongue itself is covered with teeth. In that grotesque and monstrous bird the toucan, whose bill is nearly as large as its whole body, the tongue is lined with a bundle of feathers, of the use of which, however, we are totally ignorant, though it is probably an organ of taste.

In the crab and lobster tribes the teeth are placed in the stomach, the whole of which is a very singular organ. It is formed on a bony apparatus, and hence does not collapse when empty. The teeth are inserted into it round its lower aperture or pylorus: their surface is extremely hard, and their margin serrated or denticulated, so that nothing can pass through the opening without being perfectly comininuted. The bones and teeth are moved by peculiar muscles. It is a curious fact, that at the time the animal throws off its shell, it also disgorges its bony stomach and secretes a new one.

The teeth of the cutile-fish are arranged not very differently, being situated in the centre of the lower part of the body; they are two in number, and horny, and in their figure exactly resemble the bill of a parrot.

The teeth of the echinus genus (sea-hedgehog) are of a very singulararrangement. A round opening is left in the centre of the shell for the entrance of the food: a bony structure, in which five teeth are inserted, fills up this aperture; and as these parts are moveable by numerous muscles, they form a very complete organ of mastication.

Such is the variety which the hand of nature, sometimes, perhaps, sportive, but always skilful, has introduced into the structure and arrangement of the teeth of animals, or the organs that are meant to supply their place.

The SKIN AND ITS APPENDAGES offer an equal diversity, and constitute the next subjeet of our inquiry.

All living bodies, whether animal or vegetable, are furnished with this integument: in all of them it is intended as a desence against the injuries to which, by their situation, they are commonly exposed; and in most of them it also answers the purpose of an emunctory organ, and throws off from the body a variety of fluids, which either serve by their odour to distinguish the individual, or are a recrement eliminated from its living materials.

This integument accompanies animals and vegetables from their first forma. tion: it involves equally the seed and the egg; and possessing a nature less corruptible than the parts it encloses, often preserves them uninjured for many years, till they can meet with the proper soil or season for their healthy and perfect evolution.

This is a curious subject, and must not be too hastily passed over. After fish-ponds have been frozen to the very bottom, and all the fishes contained in them destroyed; or after they have been completely emptied, and cleared of their mud; eels and other fishes have been again found in them, thougn no attempt has been made to restock the ponds. Whence has proceeded this reproduction ? Many of the ancient schools of philosophy, and even some of those of more modern date, refer us to the doctrine of spontaneous generation, and believe that they have here a clear proof of its truth. But this is 10 account for a difficulty by involving ourselves in one of a much greater magnitude. It is a petitio principië which we stand in no need of, and which we should be careful how we concede. The reproduced fishes have alone arisen from the ova of those which formerly inhabited the fish-pond; and which, from some cause or other, had sunk so deep into the soil, as to be beyond the germinating influence of the warmth and air contained in the supernatant water, communicated to it by the sun and the atmosphere. But the indestructible texture of the integument which enclosed the secundated ova has preserved them, perhaps for years, from injury and corruption; and they have only waited for that very exposure to light, air, and warmth, which the removal of the superior stratum of mud has produced, to awaken from their dormant state into life, form, and enjoyment; and but for which they would have remained in the same state, dormant but not destroyed, for ten or twelve times as long a period.

So, in the hollows upon our waste lands, when they have been for some time filled with stagnant water, we not unfrequently find eels, minnows, and other small species of the carp genus, leeches,* and water insects, and wonder how they could get into such a situation. But the mud which has been emptied out of the preceding fish-pond has perhaps been thrown into these very hollows; or the ova of the animals have been carried into the same place by some more recondite cause; and they have been waiting, year after year, for the accidental circumstance which has at length arrived, and given them the full influence of warmth, water, light, and air.

The ova of many kinds are peculiarly light, and almost invisibly minute. They are hence, when the mud, which has been removed from fish-ponds becomes dry and decomposed into powder, swept by the breeze into the atmosphere, from which they have occasionally descended into the large tanks which are made in India as reservoirs for rain-water; and producing their respective kinds in this situation, have appeared, to the astonishment of all beholders, to have fallen from the clouds with the rain itself. Dr. Thomson, in adverting to this curious fact, observes that it is difficult to account for it satisfactorily.f The explanation now offered will, if I mistake not, sufficiently meet the case.

Many insects can only be hatched in a particular animal organ; and it is the office of the integument of the ovum to preserve it in a perfect state till it has an opportunity of reaching its proper nidus. Thus the horse-gadfly, or oestrus equi, deposites its eggs on the hairs of this animal, and sticks them to the hair-roots by a viscous matter which it secretes for this purpose. But here they could never be hatched, though they were to remain through the whole life of the horse: their proper nidus is the horse's stomach or intestines, and to this nidus they must be conveyed by some means or other; and in their first situation they must remain and be preserved, free from injury or corruption, till they can obtain such a conveyance. The integument in which they are wrapped up gives them the protection they stand in need of; and the itching which they excite in the horse's skin compels him to lick the itching part with his tongue; and by this simple contrivance the ova of the gadily are at once conveyed to his mouth, and pass with the food into the very nidus which is designed for them.

It is the same integument that, by its incorruptibility, preserves the caterpillar during the torpitude of its chrysalid state, while suspended by a single ihread from the eaves of an incumbent roof; and which thus enables the worm to be transformed into a butterfly. The larve of the gnat, when approaching the same defenceless state, dives boldly into the water, and is protected by the same indestructible sheath from the dangers of an untried element.

In several species the insect remains in its chrysalid state for many years . the locust, in one of its species at least, the cicada septendecim, appears in numbers once only in seventeen years, and the palmer-worm once only in thirty years; cycles not recognised by the meteorologist, but which are well entitled to his attention : and, through the whole range of their duration, it is the integument we are now speaking of that furnishes the animal with a secure protection.

Whence comes it that plants of distant and opposite climates (for every

• See Willd. p. 120, note.

† Annals of Philos. viii. p. 70.

climate has its indigenous plants as well as its indigenous animals) should so frequently meet together in the same region ? that those which naturally belong to the Cape of Good Hope should be found wild in New-Holland ? and those of Africa on the coast of Norway? and that the Floras of every climate under the heavens should consociate in the stoves and gardens of our own country? It is the imperishable nature of the integument that surrounds their seeds by which this wonder is chiefly effected. Some of these seeds are provided with little hooks, and fasten themselves to the skins of animals, and are thus carried about from place to place; others adhere by a native glue to the feathers of water-fowls, and are washed off in disiant seas; while a third sort are provided by nature with little downy wings, and hence rise into the atınosphere, and are blown about by the breezes towards every quarter of the compass. of this last kind is the light seed of the betula alba, or birch-tree; which, in consequence, is occasionally seen germinating on the summit of the loftiest rocks and the tops of the highest steeples. * But it is to man himself that this dissemination of plants is chiefly owing. He who in some sort commands nature-who changes the desert into a beautiful landscape-who lays waste whole countries, and restores them to their former fruitfulness-is the principal instrument of enriching one country with the botanical treasures of all the rest. Wars, migrations, and crusades, travel, curiosity, and commerce, have all contributed to store Europe with a multitude of foreign productions, and to transplant our own productions into foreign quarters. Almost all the culinary plants of England, and the greater number of our species of corn, have reached us from Italy or the East ;t America has since added some; and it is possible that Australia may yet add a few more.

The utmost period of time to which seeds may hereby be kept, and be enabled to retain their vital principle, and consequently their power of germination, has not been accurately determined; but we have proofs enough to show that the duration may be very long. Thus, M. Triewald relates that a paper of melon-seeds, found in 1762, in the cabinet of Lord Mortimer, and apparently collected in 1660, were then sown, and produced flowers and excellent fruit;& and Mr. R. Gale gives an instance of a like effect from similai seeds after having been kept thirty-three years.

M. Saint-Hilaire sowed various seeds belonging to the collection of Bernard de Jussieu, forty-five years after the collection had been made. They consisted of three hundred and fifty distinct species; of these many, though not the whole, proved productive. In some the cotyledon appeared to have nearly, but not entirely, perished: in which, therefore, though the seeds swelled, and promised fairly at first, they died away gradually. And as it is a well-known fact that melons improve from seeds that have been kept for two or three years, he conceives that in this case the cotyledons have been ripened during such period.||

Animal seeds or eggs, when perfectly impregnated, appear capable of preservation as long. Bomare, indeed, affirms, that he himself found three eggs, which, protected from the action of the air, had continued fresh in the wall of a church in which they must have remained for a period of three hundred years.

The integument which covers seeds, eggs, insects, and worms, seldom consists of more than two distinct layers, and is sometimes only a single one; but in the four classes of red-blooded animals it consists almost uniformly of three layers, which are as follows: first, the true skin, which lies lowermost, is the basis of the whole, and may be regarded as the condensed external surface of the cellular substance, with nerves, blood-vessels, and absorbents interwoven in its texture; secondly, a mucous web (rete mucosum), which gives the different colours to the skin, but which can only be traced as a distinct layer in warm-blooded animals; and, thirdly, the cuticle, which covers the whole, and is furnished in the different classes with peculiar organs for the formation and excretion of a variety of ornamental or defensive materials-as hairs, feathers, wool, and silk.

* There is an interesting article on this subject published long since the above was delivered; an accoun of which may be found in the Journal

of Science and the Arts, No. vii. p. 3. † Willdenow, Principles, &c. $ 357.

Ib. vol. xliii. Tilloch's Phil. Mag. vol. xlii. p. 208, article or M. Saint-Hilaire.

11 Dictionnaire, art. Oeuf.

Phil. Trans, vol. xlii.

The cutis, or TRUE SKIN, is seldom uniforinly thick, even in the same animal: thus, in man, and other mammals, it is much thicker on the back than in the front of the body; but in the different classes or genera of animals it offers us every possible variety. Generally speaking, it is thinnest in birds, excepting in the duck tribe and in birds of prey. Its consistency and elasticity in horses, oxen, sheep, and other cattle, render it an object of high value, and lay a foundation for a variety of our most important trades and manufactures. In many animals it is so thick and tough, as to be proof against a musket-ball. It is sometimes found so in the elk, but usually so in the elephant, which, at the same time, possesses the singularity of being sensible to the sting of flies. The skin of the rhinoceros despises equally the assault of swords, musket-balls, and arrows.

I have observed already, that in many animals the skin performs the office of a muscle, though it is seldom that any thing like a fibrous structure can be traced in it. The skin of man offers a few partial instances of this power, as in the forehead and about the neck. In most quadrupeds we trace the power extending over the whole body, and enabling them to throw off at their option insects and other small animals that irritate them. The skin of the horse shudders through every point of it at the sound of a whip, and is said to be generally convulsed on the appearance of a lion or tiger. Birds, and especially the cockatoo and heron tribes, derive hence a power of moving at pleasure the feathers of the crest, neck, and tail; and the hedgehog, of rolling himself into a ball, and erecting his bristles by way of defence.

The colour of the skin is derived from the RETE MUCOSUM, or MUCOUS WEB, which, as I have already remarked, is disposed between the true skin and the euticle. The name of rete, or web, however, does not properly apply to this substance, for it has no vascularity, and is a mere butter-like material, which, when black, has a near resemblance in colour, as well as consistency, to the grease introduced between the nave of a wheel and its axletree. It is to this we owe the beautiful red or violet that tinges the nose and hind-quarters of some baboons, and the exquisite silver that whitens the belly of the dolphin and other cetaceous fishes. In the toes and tarsal membrane of ravens and turkeys it is frequently black; in hares and peacocks, gray; blue in the titmouse; green in the waterhen; yellow in the eagle; orange in the stork; and red in some species of scolopax or woodcock. It gives that intermixture of colours which besprinkles the skin of the frog and salamander; but it is for the gay and glittering scales of fishes, the splerdid metallic shells of beetles, and the gaudy eye-spots that bedrop the wings of the butterfly, that nature reserves the utmost force of this wonderful pigment, and sports with it in her happiest caprices.

The different colours, and shades of colours, of the human skin, are attributable to the same material. Most of these, however, are intimately connected with a very full access of solar light and heat; for a deep sun-burned skin has a near approach to a mulatto.* And hence the darkness or blackness of the complexion has been generally supposed to proceed from the effect produced upon the mucous pigment by the solar rays, and especially those of the calorific kind, in consequence of their attracting and detaching the oxygen of the pigment in proportion to the abundance with which it impinges against the animal surface, and in the same proportion setting at liberty the carbon, which is thus converted into a more or less persect charcoal. As this, however, is a subject which I shall have occasion to revert to in a distinct study upon the varieties of the human race,f it is unnecessary to pursue it any farther at present.

It is a most curious circumstance, that the children of negroes are uniformly

* Humboldt, Essai Polit. sur la Nouvelle Espagne, &c.

Series 11. Lecture iü.

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