« PrécédentContinuer »
the probable instruments of sensation. They are so voluminous in their orders, as well as in the genera helonging to the class (this single class containing, perhaps, as many species as are known to the whole twenty-four classes of the vegetable kingdom), that our time will allow us to do little more than instance the names of a few of the most common and familiar kinds, under the ordinal arrangement. The orders are seven; all insects being included under the technical names of coleopterous, hemipterous, lepidopterous, neuropterous, hymenopterous, dipterous, and apterous; or, to exchange the Greek for English terms, under those of crustaceous-winged, half-crustaceous-winged, scaly-winged, reticulate or net-work-winged, membranaceous-winged, two-winged, and wingless. From all which it is obvious that the ordinal character of insects is derived from the general idea of wings; to which I may add, that under this general idea, while the individuals of the last order are destitute of wings, and those of the last but one are only possessed of two wings, the individuals of the preceding five orders have four wings each, though not particularly specified in their ordinal names.
The COLEOPTEROUS or CRUSTACEOUS-WINGED INSECTS, constituting the FIRST ORDER, are by far the most numerous; and, as the ordinal term imports, embrace all those whose wings are of a shelly or crustaceous hardness; and are subdistinguished by the nature of their antennas as being clubbed at the end, thread-like or bristly. Among the more familiar of this order, I may mention the scarabæus or beetle-kinds, a very numerous race, equally distinguished by the metallic lustre of their wing-shells, and their attachment to dunghills, and other animal filth. The dermestes or leather-eater, the larves or grubs of one species of which are found so perpetually to prey on the bindings of books, and sometimes even on the shelves of libraries. The coccinella or lady-bird; the curculio or weavil, the larve of which is found so frequently in our filbert and hazel-nuts, and which secretes such a quantity of bile as to give the nut a bitter taste to a considerable extent beyond the place in which it is immediately seated.
The ptinus, producing in one of its species the death-watch, is another insect belonging to this order, whose solemn and measured strokes, repeated in the dead of the night, are so alarming to the fearful and superstitious; but which, as we formerly noticed, merely proceed from the animal's striking its little horny frontlet against the bedpost it inhabits, as a call of love to the other sex. The lampyris or glow-worm, the cantharis or Spanish-fly, and the forficula or earwig: the last of which is characterized by the singularity of its brooding over its own young like a hen, and only leaving them at night, when it roams abroad in quest of food for their support. A few of these, as the lady-bird and earwig, are by M. Cuvier taken away from the present order, and, with several of the ensuing, as the cockroach, locust, and grasshopper, carried to a new order, which he has named ORNITHOPTERA.
The sECOND ORDER OF Insects, entitled HEMIPTERA or half-crustaceous, and by some writers RHYNGOTA, has the two upper of the four wings somewhat hard or shelly, though less so than the preceding, while the two lower wings are for the most part soft and membranaceous. To this order belong the coccus or cochineal insect; the blatta or cockroach, of which the chaffer is a species; the gryllus or locust, of which one species is the little cheerful chirping cricket; the cicada or grasshopper, still more celebrated for its musical powers than the cricket; and the cimex or bug, celebrated also, but for powers which you will, perhaps, spare me from detailing.
The THIRD ORDER OF INSECTS, COLEOPTERA, or SCALY-WINGED, contains but three genera or kinds; and these are, the papilio or butterfly, the phalæna or common moth, and the sphinx or hawk-moth; which last has a near resemblance to both the others, and flies with a humming noise, chiefly in the morning and evening, as the moth flies chiefly in the evening and at night, and the butterfly only in the daytime. They have all a general resemblance to each other, and feed equally on the nectary of flowers: the antennas of the butterflies are mostly knobbed or clubbed at the tip; those of the moths are moniliform, those of the sphinxes tapering.
The NEUROPTEROUS INSECTS, or those with four reticulate or net-work wings, form the FOURTH ORDER of the Linnæan class; and they may be exemplified by the ephemera and hemerobius, the day-fly and May-fly of the angler, those little busy insects that surround us in countless multitudes when we waik on the banks of a river in a fine summer's evening, and the whole duration of whose life, in a perfect state, seldom exceeds two days, and often not more than as many hours; while it has comparatively a long life in its imperfect state, or previous to its metamorphosis. It is the agnatha of several entomologists. This order is not numerous, and I will therefore only add another example, the libellula or large dragon-fly, so denominated from its ferocity towards smaller insects; usually seen over stagnant waters; the more common species, libellula Virgo, possessing a beautiful, glittering, and green-blue body, with wings bluish towards the middle. The larve in its internal parts, is larger than the insect, and catches its prey at a distance, by suddenly darting forward the lower lip. The tracheæ, or respiratory organs, are singularly placed at the verge of the tail. It is the odonata of Cuvier.
The FIFTH ORDER OF INSECTS comprises the HYMENOPTERA, the piezata of some entomologists, or those possessed of four membranaceous wings, most of which are armed with a sting at the tail. They of course include the apis and vespa, or wasp and bee. To which I may add the formica or ant, the ichneumon, and the cynips or gall-fly, to which we are indebted for our gallnuts, whose peculiarities and habits I shall hereafter have an opportunity of reverting to.
The sixth ORDER OF INSECTS is denominated DIPTERA, and deviates from all the preceding in possessing only two wings instead of four. It includes among others the musca or common fly, ihe hippobosca or horse-fly, the oestris or gad-fly, the tipula or father-long-legs, and the culex or gnat. It is subdistinguished into such animals as possess a sucker with a proboscis, and such as possess a sucker without a proboscis. This order is the antliata of some entomologists.
The Last ORDER OF INSECTS differs still more largely from all that have been hitherto noticed; for it consists of those kinds that have no wings whatever, and hence the class is called aptera or wingless. To this order belong most of those insects that are fond of burrowing in animal filth upon the animal surface; as the pulex, pediculus, and acarus, the flea, louse, and itch-insect. To the same order belongs also the aranea or spider; the oniscus, wood-louse or millepede; the scorpio or scorpion, and even the cancer or crab, and lobster; the Linnæan system making no distinction between land and water animals from the difficulty of drawing a line; of which, indeed, the cancer genus is a very striking example, since one of the species, cancer curicola or land-crab, is, as we have already seen, an inhabitant of woods and mountains, and merely migrates to the nearest coast once a year for the purpose of depositing its spawn in the waters. These, however, are separated from the class of insects in M. Cuvier's classification, and form a distinct class by themselves under the name of CRUSTACEA ; while the greater part of the rest, as spiders, water-spiders, spring-tails, millepedes, centipedes, and scorpions, are also carried to a distinct order of the insect class, which he has called GNATHAPTERA, leaving to his own order of APTERA nothing more than the first three of the preceding list, the flea, louse, and tick or itch-insect.
But of all the animals belonging to this division under the Linnæan classia fication, I should mention, perhaps, on account of its singular instinctive faculties, the termes or white ant. The kind which inhabits India, Africa, and South America is gregarious, and forms a community, far exceeding in wisdom and policy the bee, the ant, or the beaver. The houses they build have the appearance of pyramids, of ten or twelve feet in height; and are divided into appropriate apartments, magazines for provisions, arched chambers, and galleries of communication. The walls of all these are so firmly cemented that they will bear the weight of four men without giving way; and on the plains of Senegal, the collective pyramids appear like villages of the natives. Their powers of destruction are equal to those of architecture; for so rapidly and dexterously will they destroy, in less bodies, food, furniture, books, clothes, and timber of whatever magnitude, leaving in every instance the merest thin surface, that a large beam will in a few hours be eaten to a shell not thicker than a page of writing paper.
It was my intention to have finished our survey of the Linnæan system in the course of the present lecture ; but the prospect swells so widely before us that it is impossible; and the remaining four classes of fishes, amphibials, birds, and mammals must be reserved for another study,
In the mean time, allow me to remark, that low and little as the tribes we have thus far contemplated may appear, they all variously contribute to the common good of animal being, and aid, in different ways, the harmonious circle of decomposition, renovation, and maturity of life, health, and enjoyment. The insect tribes, beautiful as they are in their respective liveries, may be regarded as the grand scavengers of nature. Wherever putridity is to be found, they are present to devour the substance from which it issues; and such is the extent and rapidity of their action, that it has been calculated by some na. turalists that the progeny of not more than a dozen flies will consume a dead carcass in a shorter space than a hungry lion. Thus, while they people the atmosphere they purify it; and in many instances, perhaps, and by tribes invisible to the naked eye, purge it of those noxious particles with which it is often impregnated, and which, at certain seasons, are apt to render it pestilential.
The indefatigable labour of the worm-tribes in promoting the general good is still more striking and manifest. The gordius or hair-worm perforates clay to give a passage to springs and running water; the lumbricus or earthworm pierces the soil that it may enjoy the benefit of air, light, and moisture; the terebella and terredo, the naked ship-worm and the shelly ship-worm, penetrate dead wood, and the philoas and mytilus, rocks, to effect their dissolution; while the termes or white ant, as we have just observed, attacks almost every thing within its reach, animal, vegetable, or mineral, with equal rapacity, and reduces to its elementary principles whatever has resisted the assault of every other species. The same system of warfare is, indeed, pursued among themselves; yet it is pursued, not from hate, as among mankind, but from instinct, and as the means of prolonging and extending as well as of diminishing and cutting short the term of life and enjoyment.
It has often been urged against the goodness, and sometimes against the existence, of the Deity, that the different tribes of animals are, in this manner, allowed to prey upon one another as their natural food, and that a large part of the globe is covered with putrid swamps, or wide inhospitable forests, or merely inhabited by ravenous beasts and deadly serpents.
Presumptuous murmurers! and what would your wisdom advise, were Providence to consult you upon so glaring an error ? Would you then leave every rank of animals to perish by the mere effects of old age? With the example so often before you of the misery endured by a favourite horse or a favourite dog when suffered to drain out the last dregs of existence in the midst of ease he cannot enjoy, and of food he cannot partake of,-a misery which often compels us, as an act of mercy, to anticipate his fate, even at last, by the aid of violence,-would you abandon every animal to the same wretchedness, only a hundred-fold multiplied by the horrors of want and hunger, which he must, by growing every day more infirm, be every day growing more incapable of appeasing ?-Or would you cut short the evil at once, by destroying death itself, and thus rendering every animal immortal ? They would not thank you for such an interference, nor applaud the vain benevolence that might dictate it; an interference which, by preventing the necessity for offspring, would extirpate from the animal frame its best feelings; which would extinguish the wise and harmonious distribution into sexes; and make an equal inroad on the pleasures of sense and the endearments of instinct.
It is granted, that a great part of the globe is an inhospitable wilderness; that it consists, to a considerable extent, of waste inaccessible jungle overrun by rapacious beasts and reptiles, of putrid swamps crowded by myriads of venomous insects, and of immense warrens burrowed by countless hordes of the hampster, the mole-rat, and the white ant. Even here, however, wherever life exists, it exists to those that possess it as an enjoyment; while these very scenes and these very animals only fill up what man has no occasion for, and equally and instantly disappear as soon as he presents himself, and exercises that industry and ingenuity which alone constitute his authority; and upon which alone his health and his happiness are made to depend.
But this is not all.-While in their different gradations these outcasts from man are thus enjoying life themselves, they are preparing, in the best manner possible, the various tracts they occupy for his future use and habitation. The soil that supports us, and gives us our daily bread, is nothing but a mixture of animal and vegetable materials; other substances, indeed, enter into it, but the great, the important, the active, and leavening constituent is of an organized origin. These materials, then, are perpetually forming and accumulating, and rising into an unbounded and inexhaustible storehouse of subsequent riches and plenty by the alternate generation and decomposition of the different kinds and orders of plants and animals which thus fill up, and, as we are apt to believe, encumber the regions we are contemplating; regions which, though in our own day unexplored or abandoned both by savage and civilized man. may, in that revolution of countries and of governments which is perpetually passing before our eyes, become, in some future period, the seat of universal dominion, the emporium of taste and elegance, of virtue and the sciences. So the fairest fields of Rome were formed out of the putrid Pontine marshes, and England has become what she is, from being a land of bogs and of blights, of wolves, wild boars and gloomy forests.
ON ZOOLOGICAL SYSTEMS, AND THE DISTINCTIVE CHARACTERS OF ANIMALS.
(The subject continued.) In our last lecture we took a momentary glance at the history of zoology as a science, noticed the primary features of the best methodical arrangements to which it has given rise, and made some progress towards a brief delineation of that of Linnæus, which still takes the lead amid the writers of the present day, and is hence chiefly entitled to attention in a course of popular study, generally collating it, however, with that of M. Cuvier, as we proceeded.
We observed that the Linnæan system comprehends all animals of every description whatever, under the six classes of mammals, birds, amphibials, fishes, insects, and worms. We pursued this arrangement in an ascending scale, as most consistent with the plan adopted at the opening of the present course of instruction; and commencing with the class of worms, finished with that of insects. It remains for us to prosecute the same rapid outline of inquiry through the four unexamined classes of fishes, amphibials, birds, and mammals.
Fishes are classically characterized in the Linnæan system as being always inhabitants of the water; swift in their motion, and voracious in their appetite; breathing by means of gills, which are generally united by a bony arch; swimming by means of radiate fins, and for the most part covered over with cartilaginous scales.
The class is divided into six orders; the ordinal characters being taken from the position of the ventral or belly fins, or from the substance of the gills. The orders are, apodal, fishes containing no ventral or belly fins; jugular, having the ventral fins before the pectoral; thoracic, having the ventral fins under the pectoral; abdominal, having the ventral fins behind the pectoral. In all these four, the rays or divisions of the gills are bony. In the fifth order, which is called branchiostegous, the gills are destitute of bony rays; and in the sixth, or chondropterygious order, the gills are cartilaginous; all which will be easiest explained by a few familiar examples. Into the general divisions of this class M. Cuvier has introduced no change of any importance whatever, his own sections and names running parallel with those of Linnæus.
The kind best calculated to elucidate the FIRST or APODAL ORDER, is the well known muræna or eel; since every one must have noticed, that this fish has no ventral or, indeed, under-fins of any kind. In many of its species, it has a very near approach to the serpent tribes ; insomuch that several of them are called sea-serpents, and by some naturalists are described as branches of the serpent genus. Even our own common eel, muræna Anguilla, is often observed to quit its proper element during the night, and, like the snake, to wander over the meadows in search of snails and worms.
The next genus I shall mention is the gymnotus, of which one species, gymnotus electricus, is the electric eel, an inhabitant of the rivers of South America, from three to four feet long, and peculiarly distinguished by its power of inflicting an electrical shock, so severe as to benumb the limbs of those that are exposed to it. The shock is equally inflicted whether the fish be touched by the naked hand, or by a long stick. It is by this extraordinary power, which it employs alike defensively and offensively, that the electric eel escapes from the jaws of larger fishes, and is enabled to seize various smaller fishes as food for its own use. There are, however, a few other fishes, as we shall have occasion to notice in proceeding, that possess a similar power, as the torpedo of European seas, and especially of the Mediterranean, and the electric silurus of those of Africa.