Gambar halaman

ing begins on the fourth or fifth day after the worm is hatched.

The appetite of the insect increases with its age; and is at its maximum after the fourth moulting. It has then attained its greatest size; and when the silky substance is elaborated in the reservoirs, the caterpillar ceases to eat, and soon diminishes again in size and weight. This fills a period of nine or ten days of its existence, beginning from the fourth casting-off of the skin; and now the insect begins to spin its silky sepulchre. But, in this operation, it proceeds with the greatest caution. It looks carefully for a spot upon which it can throw the first threads; and when it has made the choice, it glues one end of the threads, and by successive marches to and fro, but in various directions, it forms a netting, slight and loosely spun. After having finished this outward covering, it makes in the interior a succession of layers, to thicken thereby its spherical walls; and within three days, or three days and a half, the cocoon is finished. Were the cocoon wound circularly, and not zigzag, the unravelling, in the winding-off of the cocoon, would be regular; but probably the bag would be less strong.

In nearly the same space of time as is required for the formation of the cocoon, the caterpillar undergoes its second great transformation, and becomes a chrysalis. It first throws off its skin, with the head and jaws attached to it, and hardens on its exterior, though the interior remains soft. Its nourishment is already in its stomach, and consists of a yellowish mucus; but gradually the rudiments of the butterfly unfold themselves, the wings, the horns, and the legs becoming solid; a slight swelling of the body produces a rupture in the membrane that covers it, and by repeated efforts the butterfly is at length free; but, as yet, only within the cocoon. We have already mentioned Reaumur's remark, in regard to the help which the insect finds in the structure of its eyes, to file the cocoon. Other observers believe that it is assisted in this operation by a liquid which it discharges, and which dissolves the gum that holds the silk fibres together. In Mr Swayer's opinion, the moistening and the efforts of the head are both required, perhaps, to accomplish the task. Some believe that the extremity of the cocoon, through which the butterfly makes its escape, is always thinner than the rest.

The time requisite for the several changes, depends greatly on the temperature in which the eggs have been kept during the winter. If the heat of the apartment has been well regulated, the first moulting takes place on the fourth or fifth day after the hatching; the second begins on the eighth day; the third takes up the thirteenth and fourteenth days; and the last change takes place on the twenty-second and twenty-third days. The fifth age lasts ten days, at the end of which the caterpillars have reached their ultimate growth, being three inches in length, and are prepared to spin their cocoons. Thus thirtytwo days is the time that intervenes between the hatching, and the beginning of the cocoon.

Temperature, again, is one of the most determining causes of the continuance of the chrysalis. If the cocoons are kept in the temperature of sixty-six degrees of Fahrenheit, the butterfly makes its appearance after fifteen days; and it can be retarded to a month, as the Abbé Sauvage had occasion to ascertain, by depositing some cocoons in a vault.

The caterpillar's skin in a crumpled state, with the head, and jaws, and shell of the chrysalis, remains in the cocoon. Having gained their liberty, the moths of neither sex attempt to fly. The last great instinct of animated nature guides them to each other, and his destiny thus fulfilled, the male dies. The female crawls about, lays from two hundred to four hundred and fifty minute eggs, and dies also. The eggs, when first laid, are of a pale yellow, but in the course of eight or ten days they assume a reddish gray hue, and some time after that, a slate color. The unimpregnated and consequently sterile eggs remain yellow, and are depressed on their surface.

We must, from want of space, refer the reader to the document mentioned at the head of this article, for 'the enumeration and description of several varieties of silkworms. It will be sufficient to mention here, that there are, according to Dandolo's personal observation, first, small silkworms of three moultings; secondly, large silkworms of four moultings; thirdly, worms that produce exclusively white silk ; and fourthly, silkworms of eight crops. This latter species is, perhaps, the same with that of which Arthur Young makes mention, (Annals of Agriculture, vol. xxiii, p. 235.)

In 1815, eggs were procured from Bengal, which bred three times a year. In a letter from Prairie Haute, in St Charles county, Missouri, it is mentioned that several crops were obtained, without artificial means, from eggs that had been procured from Philadelphia. At Bethlehem, in Pennsylvania, two crops were raised.

Mr Zalmon Storrs mentions, in his letter to Governor Wolcott, that there are at least three varieties of silkworms in Connecticut. The first is the dark brown or flask worm, which,' observes he, is considered the best, the largest, and makes the most silk. The second a pale white worm, nearly or quite the size of the first, but which does not live so long, or make as much silk; and the third is a smaller, pale white worm, which passes through its transmigration twice in one season, producing two crops of silk; but as it produces less silk than either of the others at one crop, it is not much used, though the silk possesses one property, which that of the others does not; namely, when spun and used in its native state, it retains its clear whiteness, and does not turn yellow by washing and exposure to sun and air.' MS. Letter.

The silkworms are reared in the open air or in laboratories. The first method is followed in some parts of China ; and as the mean temperature of that country is not very high, it has been thought that there would not be any danger in adopting it in some parts of Europe. The Austrian government at one time directed the experiment to be tried by some of its regiments on the Illyrian and Wallachian frontiers. Mr Hazzi furnishes, in extenso, the reports of the commanding officers, and they are not of a nature to encourage any farther trial. Count Dandolo constructed, for his own use, a laboratory, which is now imitated in several parts of Italy. It is minutely described in his work Dell'Arte di governare i Bachi da Seta, and the most important details are transcribed or extracted in the congressional document. The principal object to be attended to in the erecting of such a building is, to construct it in such a manner, as to make it possible to regulate the degrees of light and air to be admitted into it, so as to correspond to the variable necessities of the worms. A free circulation of air is, however, the most indispensable condition of any room, or building, in which the business is pursued, on a great or a small scale. Considering the climate of this country, a cool and shady situation would be the principal point to be aimed at. An apparatus, invented by the Rev. Mr Swayne, offers this, among other advantages, that it requires a very moderate space, and that it can easily be kept clean, a circumstance essential to the health and preservation of the worins.

Mr Rush's report contains a wood cut of this apparatus.

When the mulberry leaves are about to appear, the eggs are


washed either with the cloth upon which they lie, or after having been carefully scraped off. They are then dried, and as the weather is not at that season warm enough, they must be deposited either in a hot-house, or in a room perfectly dry, the temperature of which can be regulated by means of a ther

The most indispensable implements and articles of furniture are a stove, several boxes of thin boards or thick pasteboard, some wicker trays or tables intended to support the boxes, and a few portable ones for transporting the young worms from one place to another. The wicker hurdles must be far enough apart to prevent the insects from wandering from bed to bed. The temperature, during the first two days, ought to be kept up to sixty-four degrees of Fahrenheit, either by artificial heat or by creating a draught to cool the internal air, according to the weather. On each of the following days, till the ninth, the temperature must be increased by two degrees; and on the three following days, it should not exceed eighty-one degrees.

The worms are formed when the eggs begin to whiten. Papers pierced with holes, proportioned to the age of the insect, are then extended upon them, with small twigs of mulberry. Healthy worms, on their first apperance, are of a dark or chestnut color, and never red or black. As their whole existence depends upon the state of forwardness of the tree upon which they feed, and as a sudden change in the weather retards sometimes the shooting of the leaves, the hatching must be regulated accordingly; and the mode of retarding it, is to diminish the heat of the laboratory. Independent of the temperature, a great deal also depends upon the quality of the eggs. The best hatching takes place between the first and third days after the eggs have been laid in the boxes. It is very essential that the worms to be reared come forth on the same day; and those of the first and after the third day are equally useless, and ought to be cast away, since the difference of their growth would render it impossible to attend equally to their necessities. According to Count Dandolo, thirty-seven thousand four hundred and forty eggs weigh an ounce; and the worms proceeding from them require, until their first moulting, a space of about seven feet square ; from that time till the second moulting, double that extent; till the third, about five times the first space; and till the fourth, eightytwo feet square. But when there is but a single room for the breeding, a greater attention must be paid to the temperature. The worms are kept on wider trays, lined with paper, turning upwards at the edges, to prevent their falling out.

The temperature ought to be kept at seventy-five degrees, the insects requiring less heat upon growing older. It is highly important however, to shelter them against sudden changes, and against transitions from moderate to violent heat.

In the breeding of no animal, is the exact quantity of food with which it must be supplied, of so great importance as in the rearing of the silkworm. Sanctorius, who passed a portion of his life on a pair of scales to ascertain the effects of perspiration upon the human body, cannot have managed his experiments with greater care than is necessary in the distribution of the mulberry leaves to the newly hatched insects. The silkworms proceeding from an ounce of eggs, consume, in their first age, seven pounds of leaves ; in the second, twenty-one pounds; in the third, sixty-nine pounds; in the fourth, two hundred and ten pounds, and in the fifth, one thousand two hundred and eighty-one pounds (French weight). The leaves must be chopped very small during the first period, and gradually less in the three following. At each moulting, the worms eat little for a short time; they become afterwards very voracious, and at last they cease to eat. The quantity of cocoons depends so much on the feeding, that the worms of one ounce of eggs, to produce one hundred and ten or twenty pounds of cocoons, require about one thousand six hundred and fifty pounds of leaf; and when only one thousand and fifty pounds of food have been expended, the same weight of eggs will give only from fifty-five to sixty pounds of cocoons. It is not indifferent whether the same quantity of cocoons proceeds from one or more ounces of eggs, for the quality is, in the one case, always better than in the other.

The following comparative results are mentioned in the document of Congress.

'If one ounce of eggs shall have produced, by the means stated, one hundred and twenty pounds of cocoons, they will be fine; three hundred and sixty, at most, will produce a pound and a half; and eleven or twelve ounces, at most, of these cocoons, will yield an ounce of exquisite, fine silk. When only fifty or sixty pounds of cocoons come from one ounce of

it may generally be

presumed, that they are of an inferior quality to the above, and it will require four hundred, at least, to make one pound and a half; and above thirteen ounces of these cocoons, instead of eleven or

« SebelumnyaLanjutkan »