From this it will be manifest that we have hitherto chiefly listened to the voice of Physiology in this little book, although the leading particulars of the Anatomy of the insect in its various stages have also been brought before us. We must now address ourselves for some little time to learn, from the combined sciences of Anatomy and Physiology, the structure and uses of the different organs, and their principal parts, in the insect, in the _imago_ or perfect state. In order to follow the account we shall have to give the reader, it will be convenient to take some common insect, such as a _wasp_, and fix in the memory the names of the various parts we shall have to distinguish, in thus treating of the _imago_-insect. A dragon-fly is a good example also. We shall first mention the general arrangement of the insect's structure; and subsequently take up each part separately.
It must first be mentioned, that insects possess no _internal_ bony skeleton, like that possessed by ourselves and many other animals. If we were to cut open the dead body of a fly, we should look in vain for anything like the back-bone, or the bones of the legs. But it must not, therefore, be thought that insects have no skeleton at all. Their skeleton is the thick, hard, horny substance which forms their external covering. In the wasp, for instance, it will be easily perceived, on pressing the head or the trunk of the insect between the fingers, that there is a very firm, solid coating, protecting the tender and delicate organs within. It is a very singular fact that the wisdom of the Creator has so ordered this outside coating, that where it is most necessary to be strong, as for example, when an insect has to burrow through the ground, or is in danger of being often crushed, there its thickness is greatest; and again where, as in the case of those insects which live chiefly in the air, this thickening is less necessary, because there is less risk of injury to its body, there the external covering is thinner and softer. So extraordinarily is one insect strengthened in its external coats, that it is scarcely possible to crush it by the hardest squeezing between the thumb and fingers. It has, on this account, been compared to a once famous London character, called "_Leather-coated Jack_," who used to suffer carriages to be driven over his body without receiving any harm!
