a rupture in the membrane that covers it, and, by repeated efforts, the moth bursts through the leathery envelope into the chamber of the cocoon. It thence forces its way into the open air. It is the middle portion of the cocoon, after removing the floss, or loose silk on the exterior, which is used in our manufactures. The insect must spin the whole of this without interruption, as we learn from the fact of the cocoon being generally unwound without breaking the thread. The length of an unbroken thread varies from six hundred to one thousand feet; and as it is all spun double by the insect, it will amount to nearly two thousand feet of silk, the whole of which does not weigh above three grains and a half. Five pounds of silk from ten thousand cocoons, is considerably above the usual average. When we consider, therefore, the enormous quantity of silk which is used at present, the number of worms employed in producing it will almost exceed our comprehension. The manufacture of silk, indeed, gives employment, and furnishes subsistence, to several millions of human beings.* In ancient times, the manufacture of silk was confined to the East Indies and China. The origin of this useful and beautiful substance was altogether unknown to the Roman authors, who have given ear to the most ridiculous fables respecting it. The insects at last were transported to Persia, and the Emperor Justinian introduced. them into Constantinople, having obtained them by means of two monks, who concealed them in canes, and conveyed them to the island of Cos. The scarcity of silk at no very distant date, is amusingly enough exemplified by the fact, that James I., before his accession to the crown of England, had to borrow *The silk trade of Great Britain at present may be valued at £7,000,000 sterling. The silk importations from France, through the Custom-house, amount to from £450,000 to £500,000; and by smuggling, to £250,000 or £300,000 more, making in all from £750,000 to £800,000. Manufactured silk, to the amount of £6,000,000 sterling, is consumed in England alone. What must be the amount throughout the world !-See Ure's Philosophy of Manufactures, pp. 246, 247. of the Earl of Mar a pair of silk stockings to appear in before the English ambassador. The culture of silk, as an article of commerce, has been attempted in Great Britain, but without success. It was successively introduced into Greece, Arabia, Spain, Italy, and France. It has also found its way into America, and is successfully cultivated in almost all the southern countries of the temperate zone. How curious is the Providential provision, by which a little insect, in following a natural instinct for its own preservation, is the means of furnishing to man one of his most esteemed and ornamental articles of clothing. It is, however, quite analogous to many other arrangements by which the comfort and improvement of the human race are promoted. * SIXTH WEEK-TUESDAY. INSECT TRANSFORMATIONS.-THEIR LARVA STATE. THE first state in which an insect appears when it is separated from the egg, is that of a caterpillar or grub, or of a maggot or worm, the former being furnished with feet, and the latter not. Both are by naturalists called larvæ. I shall not enter into any scientific details as to the nature of the animal in this state, but shall confine myself to the mention of one or two curious particulars. With regard to the general appearance of the common caterpillar tribe, it is not easy to give a description which will answer for them all. One of the most conspicuous of the class is thus graphically portrayed by Isaac Walton. "The very colors of caterpillars, as one has observed, are elegant and beautiful. I shall, for a taste of the rest, describe one of them,† which I will sometime the next * [On a small scale, silk has been cultivated for several years in New England. Large speculations are at present (1839) going on in different kinds of mulberry trees, which show that attention is widely awake to the subject of silk-growing, though it is not easy to predict the issue.— AM. ED.] The press-moth. month show you feeding on the willow-tree, and you shall find him punctually to answer this very description; his lips and mouth somewhat yellow; his eyes black as jet; his forehead purple; his feet and hinder parts green; his tail two-forked and black; the whole body stained with a kind of red spots, which run along the neck and shoulderblade, not unlike the form of St. Andrew's cross, or the letter X, made cross-wise, and a white line drawn down his back to his tail; all which adds much beauty to his whole body." "And it is to me observable," this pleasing old writer continues, "that at a fixed age this caterpillar gives over to eat, and towards winter comes to be covered over with a strange cell or crust, called an aurelia, and so lives a kind of dead life, without eating, all the winter. And as others, of several kinds, turn to be several kinds of flies and vermin the spring following, so this caterpillar then turns to be a painted butterfly."* But there is another kind of larva, called a water-grub, whose history is still more remarkable. One species is the produce of the gnat, the extraordinary instinct of which, in constructing a boat of its eggs, I have elsewhere described. These eggs fall to the bottom of the water, where they remain till they are hatched. They then become grubs, whose element is the water. Their organs for breathing, which are very singular, are not situated in the head, as in the higher species of animals, nor in the sides, as in caterpillars, but in the tail. A tube, for the purpose of respiration, goes off from the terminal ring of the body at an angle. Its main buoys are this tube and its tail, both of which end in a sort of funnel, composed of hairs, in form of a star, anointed with oil, so as to repel the water. It is thus suspended with its tail upward, so as to reach the surface, and its head constantly immersed to the extent of its body in the water, where, doubtless, it procures its supplies of nourishment. If the oil be removed from these hairs, the grub will sink to the bottom. "I have on these occasions," says Swammerdam, "observed it put its tail in its mouth, and afterwards draw it back, as a waterfowl will draw its feathers through its bill to prepare them for resisting water."* The air, which enters into several openings in the breathing-tube, passes onwards to two lateral windpipes, very similar to those of caterpillars. When it wishes to descend to the bottom of the water, it folds up the hairs of the funnel; but by means of its oil retains at their ends a globule of air; and when it wishes to reascend, it has only to open its airfunnel again. There are other flies besides the gnat whose grubs are aquatic, and one is mentioned by Swammerdam, that of the chameleon fly, whose air-funnel is extended to a considerable length from its terminal ring, and is fringed at the end with a beautiful star-like funnel of thirty feathers. These repel water like those of the gnat-grub, and at the point where the insect hangs suspended, a small dimple may be observed in the surface of the water. This grub also carries a globule of air with it, for the purpose of breathing, enclosed in its brush, when it descends to the bottom, which may be seen there, shining like a brilliant pearl. There is another two-winged fly, the grub of which seeks its food among ooze and mud, and whose breathing tube, while in the larva state, can at pleasure be elongated to twelve times the length of its body; the obvious intention being to keep up a communication with the external air, at such depth as is necessary for it while seeking its food. "For my part," says the naturalist above-mentioned, "I dare boldly affirm, that the incomprehensible greatness of the Deity, manifests itself in these operations in a particular manner, and affords us an opportunity of examining, as it were, with our senses, the Divine Nature."t The larvæ of the dragon-fly procure air below the water, partly by means of an apparatus for pumping; and the water thus drawn in is thrown out again at its tail, with such force as to serve, by the resistance of the stationary * Biblia Naturæ, Part i. p. 154. mass of water, and by creating a counter current, as the means of its moving from place to place; while the reverberatory stream brings small water-insects within its reach. I have mentioned this grub, chiefly for the purpose of introducing an amusing account, given by Kirby and Spence, of the instruments by which it secures and masticates its food. "The underlip is by far the largest organ of its mouth, which, when closed, it entirely conceals, and the animal not only retains, but actually seizes its prey, by means of a very singular pair of jaws, with which it is furnished. Conceive your underlip to be horny instead of fleshy, and to be elongated perpendicularly downwards, so as to wrap over your chin, and to extend to its bottom; that this elongation is there expanded into a triangular convex plate, attached to it by a joint, so as to bend upwards again, and fold over the face as high as the nose, concealing not only the chin and the first-mentioned elongation, but the mouth and part of the cheeks; conceive, moreover, that, at the upper end of this last-mentioned plate, are placed other convex ones, so broad as to cover the whole nose and temples ;-that these can open at pleasure transversely like a pair of jaws, so as to expose the nose and mouth; and that their minor edges, where they meet, are cut into numerous sharp teeth or spines, or armed with one or more sharp claws; you will then have as accurate an idea as my powers of description can give of the strange conformation of the underlip of the larva of the Libellulina, [the dragon-fly,] which conceals the mouth and face, precisely as I have supposed a similar construction of your lip would do yours. will probably admit that your own visage would present an appearance not very engaging, while concealed by such a mask; but it would strike still more awe into the spectators, were they to see you first open the two upper jaw plates, which would project, from each temple, like the blinders of a horse; and next, having, by means of the joint at your chin, let down the whole apparatus, and uncovered your face, employ them in seizing any food that presented itself, and conveying it to your mouth. Yet this procedure is that adopted by the larva of the dragon You |