Chamberss Edinburgh Journal, No. 437 | Page 8

good old times, when crossing-sweepers grew rich, and bequeathed fortunes to their patrons.

INSECT WINGS.
Animals possess the power of feeling, and of effecting certain movements, by the exercise of a muscular apparatus with which their bodies are furnished. They are distinguished from the organisations of the vegetable kingdom by the presence of these attributes. Every one is aware, that when the child sees some strange and unknown object he is observing start suddenly into motion, he will exclaim: 'It is alive!' By this exclamation, he means to express his conviction that the object is endowed with animal life. Power of voluntary and independent motion and animal organisation are associated together, as inseparable and essentially connected ideas, by even the earliest experience in the economy and ways of nature.
The animal faculty of voluntary motion, in almost every case, confers upon the creature the ability to transfer its body from place to place. In some animals, the weight of the body is sustained by immersion in a fluid as dense as itself. It is then carried about with very little expenditure of effort, either by the waving action of vibratile cilia scattered over its external surface, or by the oar-like movement of certain portions of its frame especially adapted to the purpose. In other animals, the weight of the body rests directly upon the ground, and has, therefore, to be lifted from place to place by more powerful mechanical contrivances.
In the lowest forms of air-living animals, the body rests upon the ground by numerous points of support; and when it moves, is wriggled along piecemeal, one portion being pushed forward while the rest remains stationary. The mode of progression which the little earthworm adopts, is a familiar illustration of this style of proceeding. In the higher forms of air-living animals, a freer and more commodious kind of movement is provided for. The body itself is raised up from the ground upon pointed columns, which are made to act as levers as well as props. Observe, for instance, the tiger-beetle, as it runs swiftly over the uneven surface of the path in search of its dinner, with its eager antenn? thrust out in advance. Those six long and slender legs that bear up the body of the insect, and still keep advancing in regular alternate order, are steadied and worked by cords laid along on the hollows and grooves of their own substance. While some of them uphold the weight of the superincumbent body, the rest are thrown forwards, as fresh and more advanced points of support on to which it may be pulled. The running of the insect is a very ingenious and beautiful adaptation of the principles of mechanism to the purposes of life.
But in the insect organisation, a still more surprising display of mechanical skill is made. A comparatively heavy body is not only carried rapidly and conveniently along the surface of the ground, it is also raised entirely up from it at pleasure, and transported through lengthened distances, while resting upon nothing but the thin transparent air. From the top of the central piece--technically termed thoracic--of the insect's body, from which the legs descend, two or more membraneous sails arise, which are able to beat the air by repeated strokes, and to make it, consequently, uphold their own weight, as well as that of the burden connected with them. These lifting and sustaining sails are the insect's wings.
The wings of the insect are, however, of a nature altogether different from the apparently analogous organs which the bird uses in flight. The wings of the bird are merely altered fore-legs. Lift up the front extremities of a quadruped, keep them asunder at their origins by bony props, fit them with freer motions and stronger muscles, and cover them with feathers, and they become wings in every essential particular. In the insect, however, the case is altogether different. The wings are not altered legs; they are superadded to the legs. The insect has its fore-legs as well as its wings. The legs all descend from the under surface of the thoracic piece, while the wings arise from its upper surface. As the wings are flapping above during flight, the unchanged legs are dangling below, in full complement. The wings are, therefore, independent and additional organs. They have no relation whatever to limbs, properly so called. But there are some other portions of the animal economy with which they do connect themselves, both by structure and function. The reader will hardly guess what those wing-allied organs are.
There is a little fly, called the May-fly, which usually makes its appearance in the month of August, and which visits the districts watered by the Seine and the Marne in such abundance, that the fishermen of these rivers believe it is showered down from heaven, and