|March 16, 2012||Filled under All text of Paley Natural Theology, Chapter 19||
We are not writing a system of natural history; therefore we have not attended to the classes into which the subjects of that science are distributed. What we had to observe concerning different species of animals, fell easily, for the most part, within the divisions which the course of our argument led us to adopt. There remain, however, some remarks upon the insect tribe, which could not properly be introduced under any of these heads; and which therefore, we have collected into a chapter by themselves.
The structure, and the use of the parts of insects, are less understood than that of quadrupeds and birds, not only by reason of their minuteness, or the minuteness of their parts (for that minuteness we can in some measure follow with glasses,) but also by reason of the remoteness of their manners and modes of life from those of larger animals. For instance: insects, under all their varieties of form, are endowed with antennae, [Pl. XXXII. fig. 2, 3.] which is the name given to those long feelers that rise from each side of the head; but to what common use or want of the insect kind, a provision so universal is subservient, has not yet been ascertained: and it has not been ascertained because it admits not of a clear, or very probable comparison, with any organs which we possess ourselves, or with the organs of animals which resemble ourselves in their functions and faculties, or with which we are better acquainted than we are with insects. We want a ground of analogy. This difficulty stands in our way as to some particulars in the insect constitution, which we might wish to be acquainted with. Nevertheless, there are many contrivances in the bodies of insects, neither dubious in their use, nor obscure in their structure, and most properly mechanical. These form parts of our argument.
I. The elytra, or scaly wings of the genus of scarabæus or beetle, furnish an example of this kind. The true wing of the animal is a light transparent membrane, finer than the finest gauze, and not unlike it. It is also, when expanded, in proportion to the size of the animal, very large. In order to protect this delicate structure, and perhaps also to preserve it in a due state of suppleness and humidity, a strong hard case is given to it, in the shape of the horny wing which we call the elytron. When the animal is at rest, the gauze wings lie folded up under this impenetrable shield. When the beetle prepares for flying, he raises the integument, and spreads out his thin membrane to the air. And it cannot be observed without admiration, what a tissue of cordage, i.e. of muscular tendons, must run in various and complicated, but determinate directions, along this fine surface, in order to enable the animal, either to gather it up into a certain precise form, whenever it desires to place its wings under the shelter which nature hath given to them; or to expand again their folds when wanted for action. [Pl. XXXII. fig. 1.]
In some insects, the elytra cover the whole body; in others, half; in others, only a small part of it; but in all, they completely hide and cover the true wings. [Pl. XXXII. fig. 2.]
Also, many or most of the beetle species lodge in holes in the earth, environed by rough substances, and have frequently to squeeze their way through narrow passages; in which situation, wings so tender, and so large, could scarcely have escaped injury, without both a firm covering to defend them, and the capacity of collecting themselves up under its protection.
II. Another contrivance, equally mechanical and equally clear, is the awl or borer, fixed at the tails of various species of flies; and with which they pierce, in some cases, plants; in others, wood; in others, the skin and flesh of animals; in others, the coat of chrysalis of insects of a different species from their own; and in others even lime, mortar, and stone. I need not add, that having pierced the substance, they deposit their eggs in the hole. The descriptions which naturalists give of this organ, are such as the following: it is a sharp-pointed instrument, which, in its inactive state, lies concealed in the extremity of the abdomen, and which the animal draws out at pleasure, for the purpose of making a puncture in the leaves, stem, or bark, of the particular plant which is suited to the nourishment of its young. In a sheath which enclosed a compact, solid, dentated stem, along which runs a gutter or groove, by which groove, after the penetration is effected, the egg, assisted in some cases by a peristaltic motion, passes to its destined lodgement87. In the œstrus or gad-fly, the wimble draws out like the pieces of a spy-glass; the last piece is armed with three hooks, and is able to bore through the hide of an ox. Can anything more be necessary to display mechanism, than to relate the fact? [Pl. XXXII. fig. 3, 4.]
III. The stings of insects, though for a different purpose, are, in their structure, not unlike the piercer. The sharpness to which the point in all of them is wrought; the temper and firmness of the substance of which it is composed; the strength of the muscles by which it is darted out, compared with the smallness and weakness of the insect, and with the soft and friable texture of the rest of the body; are properties of the sting to be noticed, and not a little to be admired. The sting of a bee will pierce through a goatskin glove. It penetrates the humans flesh more readily than the finest point of a needle. The action of the sting affords an example of the union of chemistry and mechanism, such as, if it be not proof of contrivance, nothing is. First, as to the chemistry; how highly concentrated must be the venom, which, in so small a quantity, can produce such powerful effects! And in the bee we may observe, that this venom is made from honey, the only food of the insect, but the last material from which I should have expected that an exalted poison could, by any process or digestion whatsoever, have been prepared. In the next place, with respect to the mechanism, the sting is not simple, but a compound instrument. The visible sting, though drawn to a point exquisitely sharp, is, in strictness, only a sheath; for, near to the extremity may be perceived by the microscope two minute orifices, from which orifices, in the act of stinging, and, as it should seem, after the point of the main sting has buried itself in the flesh, are launched out two subtile rays, which may be called the true or proper stings, as being those through which the poison is infused into the puncture already made by the exterior sting. I have said, that chemistry and mechanism are here united: by which observation I meant, that all this machinery, would have been useless, telum imbelle, if a supply of poison, intense in quality, in proportion to the smallness of the drop, had not been furnished to it by the chemical elaboration which was carried on in the insect’s body; and that, on the other hand, the poison, the result of this process, could not have attained its effect, or reached its enemy, if, when it was collected at the extremity of the abdomen, it had not found there a machinery, fitted to conduct it to the external situations in which it was to operate, viz. an awl to bore a hole, and a syringe to inject the fluid. Yet these attributes, though combined in their action, are independent in their origin. The venom does not breed the sting; nor does the sting concoct the venom. [Pl. XXXII. fig. 5.]
IV. The proboscis, with which many insects are endowed, comes next in order to be considered. [Pl. XXXII. fig. 6, 7, 8.] It is a tube attached to the head of the animal. In the bee, it is composed of two pieces connected by a joint; for if it were constantly extended, it would be too much exposed to accidental injuries; therefore, in its indolent state, it is doubled up by means of the joint, and in that position lies secure under a scaly penthouse. In many species of the butterfly, the proboscis, when not in use, is coiled up like a watch spring. In the same bee, the proboscis serves the office of the mouth, the insect having no other: and how much better adapted it is, than a mouth would be, for collecting of the proper nourishment of the animal, is sufficiently evident. The food of the bee is the nectar of flowers; a drop of syrup, lodged deep in the bottom of the corollæ, in the recesses of the petals, or down the neck of a monopetalous glove. Into these cells the bee thrusts its long narrow pump, though the cavity of which it sucks up this precious fluid, inaccessible to every other approach. It is observable also, that the plant is not the worse for what the bee does to it. The harmless plunderer rifles the sweets, but leaves the flower uninjured. The ringlets of which the proboscis of the bee is composed, the muscles by which it is extended and contracted, form so many microscopical wonders. The agility also with which it is moved, can hardly fail to excite admiration. But it is enough for our purpose to observe in general, the suitableness of the structure to the use, of the means to the end, and especially the wisdom by which nature has departed from its most general analogy (for animals being furnished with mouths are such,) when the purpose could be better answered by the deviation.
87There are numerous variations in the structure of this organ; an example of the one just mentioned is seen in the ovipositor of the buprestis, Fig. 9. It consists of three long and sharp laminæ, the two lateral ones forming a sheath to the intermediate one, which is the tube which conveys the egg. In some cases the instrument forms a saw, or what Paley here calls a dentated stem, which conveys the eggs, as in the tenthredo, cici[e.pk] cimbex, &e.—Paxton.