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animation is the desire which it evinces for obtaining food, in search of which, if not immediately supplied, it will exhibit more power of locomotion than characterizes it at any other period. So small is the desire of change on the part of these insects, that of the generality it may be said, their own spontaneous will seldom leads them to travel over a greater space than three feet throughout the whole duration of their lives. Even when hungry, the worm still clings to the skeleton of the leaf from which its nourishment was last derived. If, by the continued cravings of its appetite, it should be at length incited to the effort necessary for changing its position, it will sometimes wander as far as the edge of the tray wherein it is confined, and some few have been found sufficiently adventurous to cling to its rim; but the smell of fresh leaves will instantly allure them back. It would add incalculably to the labors and cares of their attendants, if silkworms were endowed with a more rambling disposition. So useful is this peculiarity of their nature, that one is irresistibly tempted to consider it the result of design, and a part of that beautiful system of the fitness of things, which the student of natural history has so many opportunities of contemplating with delight and admiration.

In about eight days from its being hatched, its head becomes perceptibly larger, and the worm is attacked by its first sickness. This lasts for three days; during which time it refuses food, and remains motionless in a kind of lethargy. Some have thought this to be sleep, but the fatal termination which so frequently attends these sicknesses seems to afford a denial to this supposition. The silkworm increases its size so considerably, and in so short a space of time,-its weight being multiplied many thousand fold in the course of one month,-that if only one skin had been assigned to it, which should serve for its whole caterpillar state, this skin would with difficulty have distended itself sufficiently to keep pace with the insect's growth. The economy of nature has therefore admirably provided the embryos of other skins, destined to be successively called into use; and this sickness of the worm, and its disinclination for food, may very probably be occasioned by the pressure of the skin, now become too small for the body which it encases.

At the end of the third day from its first refusal of food. the animal appears, on that account, much wasted in its bodily frame; a circumstance which materially assists in the painful operation of casting its skin: this it now proceeds to accomplish. To facilitate this moulting, a sort of humor is

thrown off by the worm, which, spreading between its body and the skin about to be abandoned, lubricates their surfaces, and causes them to separate more readily. The insect also emits from its body silken traces, which, adhering to the spot on which it rests, serve to confine the skin to its then existing position. These preliminary steps seem to call for some considerable exertion, as after them the worm remains quiet for a short space, to recover from its fatigue. It then proceeds, by rubbing its head among the leafy fibres surrounding it, to disencumber itself of the scaly covering. Its next ef fort is to break through the skin nearest to the head, which, as it is there the smallest, calls for the greatest exertion; and no sooner is this accomplished and the two front legs are disengaged, than the remainder of the body is quickly drawn forth, the skin remaining fastened to the spot in the manner already described.

This moulting is so complete, that not only is the whole covering of the body cast off, but that of the feet, of 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 magnifying lens of moderate power.

In two or three minutes from the beginning of its efforts the worm is wholly freed, and again puts on the appearance of health and vigor, feeding with recruited appetite upon its leafy banquet. It sometimes happens that the outer skin refuses to detach itself wholly, but breaks and leaves an annular portion adhering to the extremity of its body, from which all the struggles of the insect cannot wholly disengage it. The pressure thus occasioned induces swelling and inflammation in other parts of the body, and, after efforts of greater or less duration, death generally terminates its sufferings.

Worms newly freed from their exuviæ are easily distinguished from others by the pale color and wrinkled appearance of their new skin. This latter quality, however, soon disappears, through the repletion and growth of the insect, which continues to feed during five days. At this time its length will be increased to half an inch; when it is attacked by a second sickness, followed by a second moulting, the manner of performing which is exactly similar to that already described. Its appetite then again returns, and is indulged during other five days, during which time its length increases to three quarters of an inch: it then undergoes its third sickness and moulting. These being past, in all respects like the former, and five more days of feeding having

followed, it is seized by its fourth sickness, and casts its skin for the last time in the caterpillar state. The worm is now about one and a half or two inches long. This last change completed, the silkworm devours its food most voraciously, and increases rapidly in size during ten days.

The silkworm has now attained to its full growth, and is a slender caterpillar from two and a half to three inches in length. The peculiarities of its structure may be better examined now than in its earlier stages. It can readily be seen* that the worm has twelve membranous rings round its body, parallel to each other, and which, answering to the movements of the animal, mutually contract and elongate. It has sixteen legs, in pairs: six in front, which are covered with a sort of shell or scale, are placed under the three first

Fig. 1.

rings, and cannot be either sensibly lengthened, or their po sition altered. The other ten legs are called holders: these are membranous, flexible, and attached to the body under the rings. These holders are furnished with little hooks, which assist the insect in climbing. The skull is inclosed in a scaly substance, similar to the covering of the first six legs. The jaws are indented or serrated like the teeth of a saw, and their strength is great considering the size of the insect. Its mouth is peculiar, having a vertical instead of a horizontal aperture; and the worm is furnished with eighteen breathing holes, placed at equal distances down the body, nine on each side. Each of these holes is supposed to be the termination

*The scale on which the worms, cocoons, chrysalis, and moths are repremented, is two thirds their usual natural size.

of a particular organ of respiration. On each side of the head, near to the mouth, seven small eyes may be discerned. The two broad appearances higher upon the head, which are frequently mistaken for eyes, are bones of the skull. The two apertures through which the worm draws its silky substance are placed just beneath the jaw, and close to each other. These orifices are exceedingly minute.

At the period above-mentioned the desire of the worm for food begins to abate: the first symptom of this is the appearance of the leaves nibbled into minute portions, and wasted. It soon after this entirely ceases even to touch the mulberry leaves; appears restless and uneasy; erects its head; and moves about from side to side, with a circular motion, in quest of a place wherein it can commence its labor of spinning. Its color is now light green, with some mixture of a darker hue. 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 color will disappear; its body will have acquired a degree of glossiness, and will have become somewhat transparent towards its neck. Before the worm is quite prepared to spin, its body will have acquired greater firmness, and be somewhat lessened in size.

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 labor 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 laborer, 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 the two orifices before described; and these fibres are brought together by means of two hooks, placed within the silkworm's mouth for the purpose. The worm in spinning rests on its lower extremity throughout the operation, and employs its

* Note V.

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. This has been compared in shape and size to a pigeon's egg. It is seldom, however, that the ball attains to so great a size. In the following representation the cocoons are drawn two thirds of the usual size, and are shown with part of the outward or floss silk removed.

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When the insect has finished its labor of spinning, it smears the entire internal surface of the cocoon with a peculiar kind of gum, very similar in its nature to the matter which forms the silk itself; and this is no doubt designed as a shield against rain for the chrysalis in its natural state, when of course it would be subject to all varieties of weather. The silken filament of which the ball is made up is likewise accompanied, throughout its entire length, by a portion of gum, which serves to give firmness and consistency to its texture, and assists in rendering the dwelling of the chrysalis impervious to moisture. This office it performs so well, that when, for the purpose of reeling the silk with greater facility, the balls are thrown into basins of hot water, they swim on the top with all the buoyancy of bladders; nor, unless the ball be imperfectly formed, does the water penetrate within until the silk is nearly all unwound.

The continual emission of the silken material during the formation of its envelope, together with its natural evaporation, uncompensated by food, causes the worm gradually to contract in bulk; it becomes wrinkled, and the rings of its

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