they happen to be situated, as the right spiracle of the prothorax or prothoracis spiraculum dextrum: the fact of a segment possessing or not possessing spiracles is of importance in classification. In the figure of the caterpillar of the privet moth, at page 82, a spiracle may be observed under each of the oblique bands which ornament its sides; and in the pupa or chrysalis of the same insect, figured at page 196, the same spiracles are still to be traced. These breathing apertures are so very obvious in the majority of caterpillars that they can scarcely have escaped the notice of the most unobserving.

From each spiracle a single trachea enters the body; this single trachea is invariable; but the systems of trachea within are on various plans; the principal are the detached trachea, and connected trachea. They are called detached when, after entering the body as a single cylindrical tube, they separate, diverge, and ramify, throughout the region in their immediate vicinity, without any obvious connexion with the trachea of the adjoining spiracles; and connected when there is a grand longitudinal trachea traversing each side of the body throughout its length, into which each spiracle sends its particular trachea, sometimes as a single tube, sometimes after a slight ramification.

Whether the trachea possess the detached or connected form, their minute branches may be traced wandering over to the opposite side of the insect, and uniting with similar minute branches emanating from that side, so that the system of respiration is always connected, and acts by uniformity of impulse. The ramifications of the trachea, to our perception, appear infinite; they pervade the skin, muscles, nerves, stomach, intestines, legs, wings, and all the organs of sensation; the organs of respiration are therefore more generally diffused in insects than in other animals The blood of animals, in order to maintain its vital powers,

requires supplies of oxygen, which is a principal ingredient of atmospheric air: an animal, therefore, in breathing the air, divides the oxygen from the other constituent parts, appropriates the former, and rejects the latter.

General Summary. In the changes which insects undergo, not only is the external appearance altered, but the organs of support, motion, sensation, digestion, and generation are also altered, and frequently those of respiration. The organs of support in insects are mostly external; they are not bones, but perform the functions of bones; no experiments have yet proved that they possess the least sensitiveness to touch, except in a few parts in which the nerves obviously ramify to the surface. The organs of motion in insects are enclosed within, and attached to, the organs of support: they are evident muscles, partly fleshy, partly tendinous, and differ in no material character from the muscles of vertebrated animals.

The organs of sensation in insects are distinctly and decidedly nerves, and in most respects resemble the nerves of vertebrated animals; they do not, however, originate in a common or concentrated brain, but in numerous incrassated bundles of nerves, which are now termed cerebroids. The usual animal senses are possessed by insects; most of them obviously. Of hearing, we find slender proof, and its seat is altogether unknown; we also rather presume than know that insects possess smell; its seat is also unknown.

The organs of digestion in insects are peculiarly simple : the alimentary canal is very short, and the intestines generally without convolutions; the food passes very rapidly, and undergoes but little alteration.

The organs of circulation are these: a longitudinal series of little hearts, now termed corcula, which receive blood by lateral apertures from the cavities of the body: the blood is transparent and colourless, it contains numerous con

sistent oat-shaped particles; it flows very regularly, and in many parts of the body with a distinct pulsation.

The organs of respiration are tubes permeating the whole body, and communicating with the air by means of lateral spiracles or openings in the sides of the insect.

Insects are long in proportion to their breadth: they are transversely divided into thirteen segments; each segment seems to possess in itself a distinct vitality. Insects are excessively tenacious of life, even to so great a degree, that heads separated from the body have eaten voraciously for hours, the food passing completely through them; and bodies without heads have occasionally flown, and have repeatedly walked about for days. Insects appear to possess no mental power; to be incapable of memory; to assume the winged state in the plenitude of perfection; to perform the acts their parents performed without the possibility of tuition or observation.

The author is aware that several repetitions occur in the course of these pages, but they appeared to him essential to make the subject perfectly clear; he hopes that those who do not see their necessity will yet pardon them. Some of these highly interesting subjects lose nothing by repe-. tition; for the mind in youth—and for such this volume is more particularly designed-is too apt to wander from the immediate subject before it, if of a somewhat abstruse character, and requires constantly to be reminded of those important, yet often uninviting truths, which must be received before any real progress can be made in science. It is the author's particular wish to instruct as well as please: to amuse by a recital of the extraordinary acts which insects perform, and to improve the understanding by showing how the parts of insects are adapted for those acts: to point out clearly the evidence of design in the structure of these apparent atoms: to demonstrate how and for what purpose

one structure differs from another: to induce a reverential reflection how far above us and our limited powers of comprehension must be that Being, whose infinite and allpervading intelligence could plan such a multiplicity of structures, each so beautifully adapted to peculiar appetites and peculiar habits, those very appetites and habits being given to the possessor in order that it should perform some important office in the economy of nature.

THE

Ꮐ Ꭱ Ꭺ Ꮇ ] .

OF

ENTOMOLOGY.

BOOK IV.

ON SYSTEM, OR CLASSIFICATION OF INSECTS.

Vast chain of being! which from GOD began,

Natures ætherial, human, angel, man,
Beast, bird, fish, insect; what no eye can see,
No glass can reach: from infinite to thee,
From thee to nothing! On superior powers
Were we to press, inferior might on ours:

Or in the full creation leave a void,

Where, one step broken, the great scale 's destroyed;
From Nature's chain whatever link you strike,
Tenth or ten thousandth, breaks the chain alike.

POPE.