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The Story Book of Science by  Jean Henri Fabre


 

 

CHAPTER XXIV

THE METAMORPHOSIS

[104]

"O
NCE enclosed in its cocoon, the caterpillar withers and shrivels up, as if dying. First, the skin splits on the back; then, by repeated convulsions that pull it this way and that, the worm with much difficulty tears off its skin. With the skin comes everything: the case of the skull, jaws, eyes, legs, stomach and the rest. It is a general tearing-off. The ragged covering of the old body is finally pushed into a corner of the cocoon.

"What do they find then in the cells of silk? Another caterpillar, a butterfly? Neither. They find an almond shaped body, rounded at one end, pointed at the other, of a leathery appearance, and called a chrysalis. It is an intermediate state between the caterpillar and the butterfly. There can be seen certain projections which already indicate the shape of the future insect: at the large end can be distinguished the antennæ and the wings tightly folded crosswise on the chrysalis.

"The larvæ of the June bug, capricorn, stag-beetle, and other beetles pass through a similar state, but with more accentuated forms. The different parts of the head, wings, legs delicately folded at their sides, are very recognizable. But all is immobile, soft, white, or even transparent as crystal. [105] This insect in outline is called a nymph. The name of chrysalis used for butterflies and that of nymph used for the other insects signify the same thing under somewhat different appearances. Both the chrysalis and the nymph are insects in process of formation—insects closely wrapped in swaddling clothes, under which is finished the mysterious operation that will change their first structure front top to bottom.

"In a couple of weeks, if the temperature is favorable, the chrysalis of the silkworm opens like a ripe fruit, and from its burst shell the butterfly escapes, all ragged, moist, scarcely able to stand on its trembling legs. Open air is necessary for it to gain strength, to spread and dry its wings. It must get out of the cocoon. But how? The caterpillar has made the cocoon so solid and the butterfly is so weak! Will it perish in its prison, the poor little thing! It would not be worth the trouble of going through so much to stifle miserably in the close cell, just as the end is attained!"

"Could it not tear the cocoon open with its teeth?" asked Emile.

"But, my innocent child, it has none, nor anything like them. It has only a proboscis, incapable of the slightest effort."

"With its claws then?" suggested Jules.

"Yes, if it had any strong enough. The trouble is, it is not provided with any."

"But it must be able to get out," persisted Jules.

"Doubtless it will get out. Has not every creature resources in the difficult moments of life! To [106] break the hen's egg that imprisons it, the tiny little chicken has at the end of its beak a little hard point made on purpose; and the butterfly is to have nothing to open its cocoon? Oh, yes! But you would never guess the singular tool that it will use. It will use its eyes—"

"Its eyes!" interrupted Claire in amazement.

"Yes. Insects' eyes are covered with a cap of transparent horn, hard and cut in facets. A magnifying glass is needed in order to distinguish these facets, they are so fine; but, fine as they are, they have sharp bones which all together can, in time of need, be used as a grater. The butterfly begins then by moistening with a drop of saliva the point of the cocoon it wishes to attack, and then applying an eye to the spot thus softened, it writhes, knocks, scratches, files. One by one the threads of silk succumb to the rasping. The hole is made, the butterfly comes out. What do you think about it? Do not animals sometimes have intelligence enough for four? Which of us would have thought of forcing the prison walls by striking them with the eye?"

"The butterfly must have studied a long time to think of that ingenious way?" queried Emile.

"The butterfly does not study, does not reflect; it knows at once what to do and how to do well whatever concerns it. Another has reflected for it."

"Who?"

"God himself! God, the great wise one. The silkworm butterfly is not pretty. It is whitish, tun-bellied, heavy. It does not fly like the others from flower to flower, for it takes no nourishment. As [107] soon as it is out of the cocoon, it sets to work laying eggs; then it dies. Silkworm eggs are commonly called seed, a very good term, for the egg is the seed of the animal as the seed is the egg of the plant. Egg and seed correspond. They do not stifle all the cocoons in the vapor to wind them afterwards; they keep out a certain number so as to obtain butterflies and consequently eggs or seeds. These are the seeds which, the following year, produce the fresh brood of worms.

"All insects that are metamorphosed pass through the four states that I have just told you about: egg, larva, chrysalis or nymph, perfect insect. The perfect insect lays its eggs, and the series of transformations begins again."


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