2. Podura.

3. Pediculus.

4. Pulex.

. Termes.

The above belong to the insecta class, or insects proper of Cuvier and Leach.

6. Acarus.

7. Phalangium. 8. Aranea.

9. Scorpio.

The above belong to the arachnoidea class of Cuvier, Lamarck, and Leach.

10. Scolopendra.

11. Julus.

The above belong to the myriapoda class of Cuvier and Leach.

PART II.

ANATOMY AND METAMORPHOSES OF

INSECTS.

It will here be necessary to exhibit an outline of the general anatomy and progressive changes of these tribes, to make the systematic description of them intelligible to the general reader.

The external organic parts of insects are four, i. e. caput, the head; truncus, the trunk; abdomen, the abdomen; and artus, the limbs or extremities.

i. CAPUT.-The head, which is an important part of most insects, is distinguishable into 1. oculi, the eyes, including the stemmata, ocelli, or little eyes, as they are sometimes called; 2. antennæ, the horns; 3. os, the mouth. Internally it contains the medullary substance, or brain. It is, in most insects, sufficiently distinct from the thorax, but closely connected with the latter in all the coleoptera order. There are, in fact, two principal modes of connexion between the head and thorax of insects; one in which the point of contact is solid, and the motion depends upon the shape of this part; another in which the articulation is formed by a ligament. In the articulation of the head by contact of the solid parts, the head has commonly, at the part answering to the neck, one or two smooth tubercles, which are received into correspondent cavities on the anterior part of the thorax. This is the case with the genera scarabæus, lucanus, cerambyx, and most other coleoptera: hence they have the power of moving the head backward or forward, and of directing the mouth downward. Sometimes, in this mode of articulation, the posterior part of the head is rounded, and turns on its axis in a correspondent socket on the anterior part of the thorax, as in the brentus, &c. The axis of motion is then in the centre of the joint, and the mouth of the insect can be directed either upward or downward, or to the right and left. A third sort of solid articulation occurs when the head is truncated behind, and joins by a flat surface either to a tubercle of the thorax or to another flat and corresponding surface, as is seen in many of the hymenoptera and diptera. In some kinds of the Fabrician attelabi, this solid articulation is accomplished

by another means: the head of the insect termi nates in a round tubercle behind, which is received into a correspondent cavity of the thorax, and the inferior edge of this cavity is notched: by this means the motions of the head are limited to one direction.

The forficula, mantis, and blatta, exhibit the ligamentous connexion of the head and thorax. In this mode of articulation, the motions of the head are remarkably free, being confined only backwards by the projection of the back. The muscles which move the head are situated within the thorax.

1. Of the eyes of insects.-Most have two, situated in the anterior part of the head; but зeveral of the aptera order more; scorpions, for instance, having six, and spiders from six to eight, And in different tribes of insects they vary greatly both in situation and appearance. They have been, therefore, distinguished into oculi approrimati, placed close together; colorati, of a different color from that of the head; concolores, of the same color with the head; contigui, touching one another; fasciati, marked with different colored stripes; fenestrati, having the pupil glassy and transparent; hemispherici, convex, like the section of a globe; inferi, placed on the under side of the head; interrupti, broken, but continued above or below; lunati, crescentshaped; obliterati, having the pupil scarcely distinguishable; pedunculati, or stipitati, elevated on a stalk or peduncle; ovales, egg-shaped; simplices, furnished with but one lens; verticales, placed on the crown of the head.

But the most important distinction of the eyes is into simple and compound; the latter being almost peculiar to themselves, and generally possessed by those insects which have but two eyes. They are reticulated, and, when magnified, are found divided into a great number of hexagonal compartments, or lenses, slightly convex, and often separated by small furrows containing a species of eyelash. Leuwenhoek reckons in each eye of the libellula, or dragon-fly, 12,544 lenses, or in both 25,088; the pictures of objects painted on such organs of vision must, of course, be some millions of times less than the images pictured on the human eye: while there is no doubt that insects still smaller have eyes adapted to discern objects some thousands of times less than themselves. To the naked eye these numerous lenses appear like net-work. Beside these eyes, many of the neuropterous and hymenopterous families have three small shining convex points placed in the middle of the head, called, by entomologists, stemmata, the utility of which was long doubted: but they are now pretty generally acknowledged to be also organs of sight. They are simple in their structure, and seem designed for viewing remote and larger objects; the other eyes smaller and nearer ones. 2. Of the antenna.-Of these there are in general two, placed on the fore part of the head. They are peculiar to insects, and are plainly distinguishable from the tentacula of the vermes in being crustaceous; and from the palpi of insects which are more numerous and placed near the mouth. The antennæ are of great moment in distinguishing the various kinds of insects:

Linné has formed is genera upon this distinction principally. We shall enumerate and explain the several different forms of them.

Setacea are those which grow gradually taper towards the extremity. Filiformes, such as are of the same thickness throughout. Moniliformes filiform, like the preceding, but consist of a series of round knobs, like a necklace of beads. Clavata such as gradually increase in size towards the extremity. Capitata are clavata, but have the extremity somewhat round. Fissiles are capitata; but have the capitulum, or knob, divided longitudinally into three or four parts, or lamina, as in the scarabæi. Perfoliata, are also capitata; but have the capitulum horizontally divided, as in the dermestes. Pectinata, so called from their similitude to a comb, though they more properly resemble a feather, as in the moths and elateres. This is most obvious in the male. Furcate, or forked, having the last joint divided into parts. Aristate, such as have a lateral hair, which is either naked or furnished with smaller hairs, as in the fly. Breviores, those which are shorter than the body. Longiores, those which are longer than the body. Mediocres, those which are of the same length with the body: the last three varieties are distinguishable in the cerambyces.

The use of these organs is yet unascertained. There is nothing analogous to them in other animals, which has induced some naturalists to suppose them to be the organ of some extremely delicate sense unknown to us: some respectable modern writers have thought them to be the seat of hearing, others of smelling, and Mr. Huber both of touch and smell.

The activity with which these organs are used, and the abundance of medullary nerves which connect them throughout with the brain, indicate the importance of them to the insect economy. Some insects which have the antennæ small have the palpi very large, as if they were intended to answer the same purpose, or partake of the same sense, as the antennæ, and thus, by their mutual aid, supply the deficiency of the latter: the larvæ of certain insects again which have palpi have no antennæ, and others in the same state have antennæ and no palpi.

Mr. Donovan says, "The antennæ appear to us to be rather connected with the organ of hearing than either that of feeling or smelling. The palpi, we have little doubt, are the organs of feeling, both from their texture and the manner in which insects are oftentimes observed to make use of them in touching their aliments; and the organs of smelling in insects, however singular it may be imagined, we conceive to be no other than the apertures disposed on each side the thorax and body. By the organs of hearing, we do not mean to consider them as external ears, but as being in some manner auxiliary to the organ of hearing, the seat of which we suspect to be contiguous to the base of the antenna, the spot in which the same organ has been discovered in the cray-fish. They may answer this and some other purpose likewise.'

Bonnet thinks the antennæ the organ of smell. 'Different insects,' he observes, have an exquisite sense of smelling, the organ of which is yet

undiscovered. May it not reside in the antennæ ? Lehmann, from the result of experiments on this subject, denies that the antennæ are the olfactory organ. He made an opening an inch wide in the side of a glass vessel, and surrounded the edge with wax, so that a close covering could be applied. An aperture was made in this covering, through which either the whole head, or the antenna only, of an insect could be introduced. By means of a tube the glass was filled with penetrating odors, vapors, or heated air; but neither the fumes of sulphur nor burnt feathers produced the smallest effect on butterflies, bees, or beetles, whose antennæ were exposed to them.

He supposes, with Mr. Donovan, that the spiracula are the seat of smelling. That insects possess the faculty of smelling, says an able writer in the Edinburgh Review, No. XII., is clearly demonstrated. It is the most perfect of all their senses. Beetles of various sorts, nitidula, the different species of dermestes, sylpha flies, &c., perceive, at a very considerable distance, the smell of ordure and dead bodies, and resort in swarms to the situations in which they occur, either for the purpose of procuring food or depositing their eggs. The blue flesh-fly, deceived by the cadaverous odor of a species of arum, alights on its flower. But though we can thus easily prove the presence of the sense of smell among insects, it is much more difficult to discover the seat of that particular sense. Several naturalists have supposed that it resides in the antennæ. Dumeril, in a dissertation published in 1799, attempts to prove that it must be situated about the entrance of the stigmata or respiratory organs, as Baster had previously supposed. His arguments, however, did not induce Latreille to relinquish the former opinion, which places it in the antennæ.'

He has assigned the following reasons for his belief: 1. The exercise of smell consists only in the action of air, impregnated with odoriferous particles, on the nervous or olfactory membrane, which transmits the sensation. If insects be endowed with an organ furnished with similar nerves, and with which air, charged with odoriferous particles, comes in contact, such an organ may be regarded as that of smell. Should the antennæ present a tissue of many nerves, what inconvenience can result from supposing that this tissue is capable of transmitting odor? Would not this hypothesis, on the contrary, be more simple and more consonant to anatomical principles than that which fixes the seat of smell at the entrance of the stigmata? Besides, this last mode of explanation will not, I presume, suit the crustaceous animals, which so nearly approach to insects. 2. Many male insects have their antennæ more developed than the females; a circumstance easily explained, if these organs are allowed to be the seat of smell. 3. Certain it is that most of those insects which live or deposit their eggs on putrid animal or vegetable matters, stagnant waters, &c., are almost uniformly distinguished by a greater development of the antennæ; such, for instance, as the scarabæus, dermestes, silpha, clerus, tenebrio, tipula, bibio, &c. These, requiring a more perfect sense of smell, are VOL. VIII,

su.tably organised. 4. A great number of insects which are entirely rapacious have simple antennæ, and those which are sedentary have none at all; such, for instance, as some of the acari, and a considerable part of Lamarck's arachnoid. 5. Insects discover their haunts and food by the sense of smell. Latreille deprived several insects of their antennæ, and found they instantly fell into a state of insensibility, and seemed to know neither their habitations nor their food, though placed close by them. Were such expe riments as this prosecuted the question might soon be decided: by coating the antennæ of insects with varnish, and placing them near their natural food, it might easily be known whether the antennæ were the organs of smell; if they were the animal could not be supposed to find its way to the food, and vice versâ. 6. Nerves terminate the antennæ, the articulations of which, though externally covered with a pretty thick membrane, are hollow, lined with a soft substance, frequently of a watery consistence, the extremities of which, when exposed to the air, may receive impressions from it.

Mr. Kirby mentions a singular circumstance respecting the antennæ of the eucera, or longhorned bee, which,' says he, 'to the best of my knowledge has never before been noticed andwhich may possibly lead to the discovery of the use of these organs. Placed under a powerful magnifier, the last ten joints appear to be composed of innumerable hexagons, similar to those of which the eyes of these insects consist. If we reason from analogy this remarkable circumstance will lead us to conjecture that the sense, of which this part so essential to insects is the organ, may bear some relation to that conveyed by the eyes. As they are furnished with no instrument for receiving and communicating the impressions of sound, similar to the ear, that deficiency may be supplied by extraordinary means of vision That the stemmata are of this description seems very probable; and the antennæ may, in some degree, answer a similar purpose: the circumstance just mentioned furnishes a strong presumption that they do this, at least in the case of these males; else why do they exhibit that peculiar structure which distinguishes the real eyes?

That insects do hear, by whatever organ, seems abundantly established. Lehmann states that, on observing a spider descend from the ceiling of a room by its thread in quest of a female, while he was reading, he began to read aloud: the animal, alarmed at the noise, retreated upwards; he was silent, and it returned; on again reading aloud, it testified alarm and ascended its thread; nor was its apprehension of danger dispelled, until familiarised with the sound or conquered by the object of its pursuit. This author deprived crickets, which are animals noted for acuteness of hearing, of the antennæ; yet they were equally sensible of sound as before. By an experiment of Huber's, it seems that a queen bee deprived of her antennæ, loses, if not her fecundity, all the ordinary characteristics by which she is known in the hive. Amputating one of the antennæ of a queen he found was not attended with any perceptible effect. Privation of

2 G

both, however, produced very singular consequences. M. Huber cut them from a queen whose fecundation had been retarded, so that she laid none but the eggs of males. From that moment a marked alteration in her conduct was seen; she traversed the combs with extraordinary rapidity, scarcely had the workers time to recede before her; and, instead of the care which a perfect queen displays in depositing her eggs in those places alone suitable for their exclusion, she dropped them at random without selecting proper cells: she retired to the most solitary parts of the hive, seeming to avoid the bees, and long remained motionless. Several workers, however, followed her there, and treated her with the most evident respect. She seldom required honey from them; but, when that was the case, she directed her trunk with a kind of uncertain feeling, sometimes on the head and sometimes on the limbs of the workers; and if she did reach their mouths it was by chance. Queens leave their hive but once in their whole lives, which is for the purpose of obtaining impregnation; they remain voluntary prisoners ever afterwards, unless in leading out a swarm. This queen, however, seemed eager to escape; she rushed towards the opening of the hive, but, finding it too small for her exit, she returned after fruitless exertion. Notwithstanding the symptoms of delirium by which she was agitated, the workers never ceased to pay her the same attention as they invariably do their queens, though she received it with indifference.' There is clearly a field of very interesting research still open to intelligent entomologists on this mysterious subject.

3. Of the mouth.-To the peculiarities in the structure of this part of the head a great degree of importance is attached by many of the modern systems of entomology having founded their essential characters, and Fabricius his classification of insects upon them. It consists of the following principal parts :—

i. The labrum, or labium, inferius, is the terminating portion of the mouth below, and sometimes lengthened so as to form the instrument called ligula. It is frequently bifid, and has the posterior pair of feelers placed at the base.

ii. The labium superius, or upper lip, is situated above the jaws, as in the scarabæus and gryllus, and is of a membranaceous nature, transverse, soft, and moveable. Linné and Fabricius are said sometimes to have confounded the upper lip with the clypeus, or shield of the head. The two parts may be distinguished by one invariable character,' says Mr. Samoulle, the clypeus is fixed, and forms a portion of the head; the upper lip is moveable, and is placed more for

ward.'

iii. Lingua, the tongue, in some insects is taper and spiral, as in the butterfly; in others it is fleshy, resembling a proboscis, and tubular, as in the fly. It constitutes the whole mouth in lepidopterous insects; and consists of two filamentous pieces, which are externally convex, concave within, and connected longitudinally by a suture along the middle both above and beneath. These, in uniting, form a cylinder, through which are drawn up the nectareous juices of the flowers on which such insects subsist.

The two pieces, being not very closely united, may be separated by a needle's point. When the insect takes its food, this tube is exserted; at other times it is deposited between the palpi in spiral folds.

iv. The mandibula, or mandibles, are two horny substances placed one at each side of the mouth, below the upper lip. They have a lateral motion, while the upper and lower lip move up and down, as in other animals; and differ from the maxillæ, with which they are often confounded, by not having any of the palpi or feelers attached to them.

v. The maxilla, or jaws, are two small pieces of a membranaceous consistency, indented at the extremity, and nearly all ciliated at the inner edge. They have a lateral motion, and are sometimes distinguished, as to their form, into dentata, i. e. set with sharp-pointed processes; forcipata, pincer-shaped; furcata, forked; lunulata, thick in the middle and smaller towards the base and the apex; prominentes, placed straight before the head.

vi. The haustellum, or the sucker, is formed of two or more very small and delicate filaments, enclosed in a sheath of two valves.

vii. The rostrum, or beak, also forms the principal part of the mouth in many of the hemipterous order of insects. It is moveable, articulated, and bent under the breast. The beak within is hollow, and contains, as in a sheath, three or more very delicate bristles, the points of which these insects introduce into the body of the animal, or substance of the plants, from which they derive their sustenance. In the cicada, nepa, and cimex, this part is very distinguishable.

viii. The proboscis is a trunk inserted in place of a mouth, in dipterous insects. It is a fleshy, retractile, single, often a cylindrical, instrument; the end forming two lips of a soft substance, and supposed, from the delicacy of their teguments, to possess the faculty of taste (as in the common fly) in an exquisite degree.

ix. Palpi, the feelers, are small, moveable, filiform, appendages to each side of the mouth in most insects, and resemble the antennæ, but are more distinctly articulated. They, as their name implies, are supposed to be the organs of touch, and vary in number in different tribes, being either two, four, or six, and are commonly inserted at each side the exterior part of the jaw. In those insects which have but one pair, they are situated generally on the upper lip; when there are two or more, the posterior ones are generally on the lower lip; and in some insects they are inserted at each side of the haustellum. Composed of joints, more or less numerous, they exhibit a considerable affinity to the antennæ, and they are endowed with equal, and even more, extensive powers of motion. They serve there fore like the antennæ, where they are found, as an essential character in the distinction of genera; for in several of the fulgore, cicada cimices, nepa, &c., of Linnæus, there are none: they abound most in the carnivorous tribes.

x. The galea, or shields of the mouth, are two membranaceous appendages, of a large size and cylindrical form, placed one on each side at the exterior and back part of the jaw, covering the