more or less rapid, is altogether an admirable mystery, forming one of the broad distinctions between the works of nature and those of imitative art. Man can form nothing capable of altering its own structure by the process of assimilation which produces growth. A single blade of grass surpasses all the productions of human skill.

Owing to this rapid growth of the worm, had its original skin been the only one assigned to it, to serve for its whole caterpillar life, it would with difficulty have distended itself sufficiently to keep pace with the increase of its length and weight. Five times, therefore, in the course of its brief existence, it undergoes the process of moulting, casting off not only the whole covering of its body, but that of the feet, the entire skull, and even the jaws, including the teeth. These several parts may be discerned by the unassisted eye, but become very apparent when viewed through a lens of moderate power. In this process, a remarkable analogy may be observed to what takes place in the vegetable world.

The buds of plants are composed of successive leaves closely embosomed within each other's foldings, the outer one being generally hard and corneous, from the exposure of its vessels to the colds of winter, while the inner leaves, being thence protected, remain soft and pulpy. But, as soon as the inner leaves receive an accession of sap, which rises from the roots on the return of spring, their vessels swell, and their nervures expand; while the outer leaf, from its vessels being shrunk and partly obliterated, undergoes little change besides being pushed out and sometimes entirely thrown off by the growth of the inner leaves which it had previously enclosed. On comparing one of the bud-envelopes thus thrown off, we can scarcely persuade ourselves that so small a covering could ever have contained the large spreading leaves which have burst from them.

A caterpillar corresponds in several circumstances to the leaf-bud. The outer skin encloses a succession of several other skins, each becoming more delicate, soft, and indistinct than the one exterior to it; but gradually, like the expanding leaves, growing more substantial and firm as it receives a supply of nutriment. The chief mechanical difference between the leaves folded up in the bud, and the successive caterpillars enveloped within the skin of one newly hatched, is, that the leaves in the bud receive all their nourishment through their footstalks from the root of the tree, whereas the caterpillar is nourished from within by the food digested in its stomach. The superfluous nourishment, usually in considerable quantity, and called the fat of the caterpillar, appears to lie between the successive skins, in a similar way to the adhesive gluten in the leaf-bud. But, as the first inner skin expands and increases in consistence, the fat which lies between it and the outer skin, seems to be absorbed into the body of the caterpillar, and of course swelling it out; while its abstraction from the interior of the outer skin renders this much more dry, separates it from

The absorp

the inner skin, and disposes it to harden and shrivel. * tion of the fat also produces the remarkable consequence of gorging all the channels of nutrition, so that there is no longer any demand upon the stomach for fresh supplies of food. The caterpillar accordingly ceases to eat, and, having no incentive to action, remains motionless. The outer skin, meanwhile, being deprived of its internal moisture by the absorption of the fat, goes on to harden and shrink, while all the internal organs become enlarged by the nutritive fat. The expansion, therefore, of the body of the caterpillar on the one hand, and the shrinking of the old skin on the other, produce a mutual struggle, which, from the continued operation of the causes, must, it is obvious, be soon brought to a termination.

The skin, from losing its internal moisture, loses also a portion of its colour, and becomes obscure and dull; and the caterpillar, from being girt and squeezed by its pressure, begins to turn and twist itself in various directions, to rid itself, if possible, of the inconvenience. By continuing these movements, the creature succeeds at length in rending the old skin at its weakest part, which is usually on the back, just behind the head; and in a few minutes, using its body as a wedge, it may be seen issuing through the breach. The old skin is thus abandoned like a worn shirt; and the caterpillar appears in an entire new dress, the tints of which are fresher and brighter, and the colours and markings often considerably different from the former. The insect, also, in consequence of the quantity of fat which has gone to augment its several parts, becomes all at once so much enlarged in size, that we can with difficulty conceive how it could have been contained in the old skin out of which it has crept. The cast skin is frequently so very perfect, that it might almost be supposed to be the caterpillar itself, particularly in those which are hairy, as this contributes to the shrivelling.' Ins. Transf. pp. 167–170.

This moulting of caterpillars, which, in some species, takes place as many as ten times, bears some slight resemblance to the casting of the feathers in birds, and the shedding of the hairy coat in quadrupeds. But, in these cases, the process is gradual and more superficial; the removing of the worn materials of the animal structure being chiefly effected by the absorbent system, which, in caterpillars, appears to be wanting. The successive changes of the skin accomplish all that is necessary in this respect: the hardening of the outer skin, which renders it less capable of distending so as to accommodate itself to the very rapid growth of the worm, seems to be necessary, that it may sufficiently answer the purpose of a sheath to

* Some writers have supposed that this fat is a sort of humour thrown off by the worm, to facilitate the moulting, which, spreading between the body and the skin about to be abandoned, lubricates their surfaces, and causes them to separate more readily.' (Lardner's Cyclop. Silk Manuf. p. 108.) But this representation does not account for the enlargement of the worm.

the tender and pulpy body, which is still further protected by the glutinous secretion or fat. It is probable, too, that the ab sorption of this fat produces a thickening of the inner skin, preparatory to its becoming the outer covering.

At length, the silk-worm has attained its full growth, and is a slender caterpillar from two and a half to three inches in length. During about ten days from its fourth moulting, it devours its food most voraciously; but, on attaining its full dimensions, its desire for food begins to abate, and it soon ceases even to touch the leaves. It now appears restless, erecting its head, and moving from side to side in quest of a place where it may commence its labour of spinning. In twenty-four hours from the time of its abstaining from food, the material for forming its silk will be digested in its reservoirs; its green colour will disappear; and before it is quite prepared to spin, its body will have acquired a degree of glossiness and greater firmness at the expense of some diminution of size. We transcribe from the Treatise on Silk in the Cabinet Cyclopædia, (reviewed in our last Number,) the account of the subsequent process.

The substance of which the silk is composed, is secreted, in the form of a fine yellow transparent gum, in two separate vessels of slender dimensions, which are wound, as it were, on two spindles in the stomach: if unfolded, these vessels would be about ten inches in length. When the worm has fixed upon some angle or hollow place, whose dimensions agree with the size of its intended silken ball or cocoon, it begins its labour by spinning thin and irregular threads, which are intended to support its future dwelling. During the first day, the insect forms upon these a loose structure of an oval shape, which is called floss silk, and within which covering, in the three following days, it forms the firm and consistent yellow ball; the labourer, of course, always remaining on the inside of the sphere which it is forming.

The silky material, which, when drawn out, appears to be one thread, is composed of two fibres, extracted through two minute orifices just below the jaw; and these fibres are brought together by means of two hooks placed within the silk-worm's mouth for the purpose. The worm, in spinning, rests on its lower extremity throughout the operation, and employs its mouth and front legs in the task of directing and fastening the thread. The filament is not spun in regular concentric circles round the interior surface of the ball, but in spots, going backwards and forwards with a sort of wavy motion. This apparently irregular manner of proceeding is plainly perceptible when the silk is wound off the ball, which does not make more than one or two entire revolutions while ten or twelve yards of silk are being transferred to the reel. At the end of the third or fourth day, the worm will have completed its task, and formed its cocoon.'

Lardner's Cab. Cycl. Vol. XXII. pp. 111, 12.

During the emission of the silken material, the worm gradually contracts in bulk, and becomes wrinkled. Its task being finished, it rests awhile, and then throws off its caterpillar garb. If the cocoon be now opened, its inhabitant will be found in the state of a chrysalis or aurelia, in shape somewhat resembling a kidney bean, but pointed at one end, having a smooth brown skin. Its former covering will be found lying beside it. In this state it remains for a period varying, according to the temperature of the climate or season, from fifteen to thirty days. It then throws off its leathery shroud, having become, in the interval, transformed into a large greyish moth, furnished with four wings, two eyes, and two black, feathery antlers. If left until this period within the cocoon, the moth takes immediate measures for her emancipation, and without saw or centre-bit, she makes her way through the shell, the silk, and the floss.' Having first, by means of a fluid discharged from its mouth, lessened the adhesiveness of the gum with which it had lined the interior surface of its chamber, the moth extends its antennæ, together with its head and feet, towards the point of the cone, and gradually loosens, without breaking, the texture of the ball: then, using its hooked feet, it pushes aside the filaments, and having sufficiently enlarged the opening, issues forth into light, leaving at the bottom of the cone the relics of its caterpillar form.

The length of the unbroken thread in a cocoon, varies from 600 to 1000 feet; and as it is all spun double by the insect, it will amount to nearly 2000 feet of silk, the whole of which does not weigh above three grains and a half. Five pounds of silk from 10,000 cocoons, is considered as above the usual average. The moth enjoys its liberty for a very brief term. Its first employment is to seek its mate; after which the female deposits her eggs; and both, in the course of two or three days after, terminate their being. The number of eggs produced by the female moth, varies from 250 to 400, or even 500.

This one specimen of insect architecture, insect manufacture, and insect metamorphosis, will serve, we hope, as well as multiplied extracts from these entomological varieties, to recommend the volumes and the study to any of our readers who have hitherto neglected this branch of entertaining and more than entertaining knowledge. The wise man sends the slothful to learn diligence of the ant. Might not the unproductive idler, clad, perhaps, in the produce of an insect, be sent to school to the silk-worm? But all nature is full of varied lessons of wisdom and piety, to those who can decipher the sacred cha

racters.

the tender and pulpy body, which is still further protected by the glutinous secretion or fat. It is probable, too, that the absorption of this fat produces a thickening of the inner skin, preparatory to its becoming the outer covering.

At length, the silk-worm has attained its full growth, and is a slender caterpillar from two and a half to three inches in length. During about ten days from its fourth moulting, it devours its food most voraciously; but, on attaining its full dimensions, its desire for food begins to abate, and it soon ceases even to touch the leaves. It now appears restless, erecting its head, and moving from side to side in quest of a place where it may commence its labour of spinning. In twenty-four hours from the time of its abstaining from food, the material for forming its silk will be digested in its reservoirs; its green colour will disappear; and before it is quite prepared to spin, its body will have acquired a degree of glossiness and greater firmness at the expense of some diminution of size. We transcribe from the Treatise on Silk in the Cabinet Cyclopædia, (reviewed in our last Number,) the account of the subsequent process.

The substance of which the silk is composed, is secreted, in the form of a fine yellow transparent gum, in two separate vessels of slender dimensions, which are wound, as it were, on two spindles in the stomach if unfolded, these vessels would be about ten inches in length. When the worm has fixed upon some angle or hollow place, whose dimensions agree with the size of its intended silken ball or cocoon, it begins its labour by spinning thin and irregular threads, which are intended to support its future dwelling. During the first day, the insect forms upon these a loose structure of an oval shape, which is called floss silk, and within which covering, in the three following days, it forms the firm and consistent yellow ball; the labourer, of course, always remaining on the inside of the sphere which it is forming.

The silky material, which, when drawn out, appears to be one thread, is composed of two fibres, extracted through two minute orifices just below the jaw; and these fibres are brought together by means of two hooks placed within the silk-worm's mouth for the purpose. The worm, in spinning, rests on its lower extremity throughout the operation, and employs its mouth and front legs in the task of directing and fastening the thread. The filament is not spun in regular concentric circles round the interior surface of the ball, but in spots, going backwards and forwards with a sort of wavy motion. This apparently irregular manner of proceeding is plainly perceptible when the silk is wound off the ball, which does not make more than one or two entire revolutions while ten or twelve yards of silk are being transferred to the reel. At the end of the third or fourth day, the worm will have completed its task, and formed its cocoon.'

Lardner's Cab. Cycl. Vol. XXII. pp. 111, 12.