Why was the manufacture of silk, in ancient times, confined to the East Indies and China?

Because the insects that produced it were indigenous to those countries. It was thence brought to Europe in small quantities, and in early times sold at so extravagant a price, that it was deemed too expensive even for royalty.

Why were silk-dresses prohibited by Mahomedans? Because they considered silk unclean, from its being produced by a worm. Hence it was decided that a person wearing a garment made entirely of silk, could not lawfully offer up the daily prayers enjoined by the Koran. Herbelot.

The history and economy of the silkworm would occupy some score pages, but these few facts are the latest illustrations.

Why are the eggs of some insects found strongly cemented round the twig of a leafless tree?

Because they may there survive the winter, and be hatched in spring; the living principle, though not in a state of activity, being capable, as it would appear, of withstanding severe cold.

Why do these caterpillars hang by a thread of silk from the branches of trees, with their head downwards? Because they may be always ready to drop down in safety, by extending this thread, on the sudden approach of their enemies.

THE COSSUS.

Why is the cossus so destructive to the trees on which it lives?

Because it exists as a caterpillar three years previous to its changing into the pupa state. It is so tenacious of life, that it will remain in an artificial vacuum for hours together, without being injured; and under water for almost three weeks in the middle of summer, It is remarkable also, that the pupa has the power of

locomotion, and when the time of its change approaches, can bore its way from the middle of the tree to the bark. Blumenbach.

Why has the caterpillar of the cossus been stated by entomologists as a specimen of the muscular strength of insects?

creature.

He

Because it contains more than seven times as many muscles as the human body, being 4061. Lyonnet has ably illustrated the anatomy of this extraordinary Mr. Rennie put one of these caterpillars under a bell-glass, which weighed nearly half-apound, and upwards of ten times the weight of the insect, yet it raised it up with the utmost ease. then placed on the glass a thick book, weighing four pounds, and the animal again raised the glass, though loaded with the book, nearly a hundred times its own weight, and made good its exit. It should, however, be mentioned, first, that the wedge-like form of the caterpillar's head, in connexion with the peculiar shape of the glass, enabled it to lift it; and, secondly, that one side of the glass resting on the table, the insect only bore half the weight of the glass and book.Insect Transformations.

NEUROPTERA.

THE DRAGON-FLY.

Why are the larger dragon-flies usually called horsestingers?

Because they are supposed to have a propensity to sting horses, and (it may be presumed) any other animal which may irritate them. But, not one of the tribe is furnished with a sting. They have, however, a pair of most formidable looking jaws, though even these are not strong enough to inflict injury upon any of the larger animals, and are only employed to crush a fly, or to wing a moth or a butterfly.

We may here mention that the larvæ of the dragon

fly are provided with an apparatus probably unmatched in the insect world. This consists of a mask, or the under lip of the larva, which conceals the mouth and face, and two plates covering the jaws. While this strange organ is at rest, it applies close to and covers the face. When the insects would use it, they unfold it like an arm, catch their prey by means of the plates, which are toothed like jaws, and then partly refold the lip, so as to hold the prey to the mouth. De Geer observes, the larvæ of the dragon-fly do not, however, trust to this mask alone, for surprising their prey, but steal upon it, as a cat does upon a bird, very slowly, and as if they counted their steps; and then, by suddenly unmasking, seize it by surprise: so artful are they, that insects, and even small fishes, find it difficult to elude their attacks.

Why do the larvæ of dragon-flies suck in and eject water to aid their progress in swimming?

Because the jet propels the creature through the water, in consequence of its being resisted by the stationary mass of the fluid behind it, and a contrary current being thence produced by this singular pumping. As the insect, between every stroke of the internal piston, is obliged to draw in a fresh supply of water, an interval consequently occurs between the strokes, during which it will sometimes elevate its tail above water, and squirt out a small stream like that from a little syringe. Among other purposes of this wonderful apparatus are its aid in bringing small water insects within its reach, and its share in respiration, in which it somewhat resembles the gills of fish.

THE DAY-FLY.

Why is the ephemera or day-fly so called? Because it lives but a very short time in its perfect state; often only for a few hours. Day-flies live in water some years as larvæ. After that time, in many

places, millions of the perfectly-formed insects make their appearance from the water, within a few days, in the middle of summer; they then also, contrary to what happens to other insects, cast their skin again.Blumenbach.

Why are water-flies less abundant than formerly? Because of the diminution of rivers and streams, and the cultivation of the country. "Thus," observes Sir H. Davy, in his Salmonia, "most of the bogs or marshes which fed considerable streams are drained; and the consequence is, that they are more likely to be affected by severe droughts and great floods; the first killing, and the second washing away, the larvæ and aurelias. May-flies, thirty years ago, were more abundant in the upper part of the Teme river, in Herefordshire, where it receives the Cluer; they are now seldom or rarely seen; and most of the rivers in that part of England, as well as those of the west, with the exception of those that rise in the still uncultivated parts of Dartmoor and Exmoor, are often rapid and unfordable torrents, and in dry summers little more than scanty rills."

THE CADDIS.

Why does the caddis-worm, or larva of the watermoth, encase itself with shells, stems, leaves, straws, &c? Because its form is but little adapted for swimming: its long body, encumbered with six legs, is specifically heavier than water, the element in which it has to seek its food; and it thus attaches itself to these bodies, to counterpoise its own excess of gravity, and enable it to swim on the surface, in the centre, or at the bottom of the water. This explains the variety and singularity in the materials of the coats of these insects. When they want to ascend, the quantity of hollow and buoyant substances attached to them is increased; in order to descend, the light and hollow substances are either diminished or counterpoised by an addition of heavy materials, such as shells or gravel; the interior they line with a fine silk spun by themselves.

HEMOROBIUS.

Why does the hemorobius perla fasten its eggs to the leaves of trees, upon upright bristle-like points ?

Because the aphis has previously laid its eggs upon these leaves, and the young aphides would destroy the above eggs, were they not thus kept out of their reach. As soon as the larvæ of the hemorobius appear, they crawl down the slender props upon which they rested, and commence devouring the aphides, wherefore the former are termed plant louse lions; and by thus thinning them, they are doubtless of great service in the general economy of nature.

ANT-LION.

Why is the ant-lion so called?

Because, when in its larva state, it digs, with its leg for a shovel, a funnel-shaped pit in the sand, and covers itself up to the neck, laying wait for and destroying the ants and other small insects, which, not perceiving it, come to the edge of the pit, and slip in over the loose sand. Like its prototype, the lion, it will not take a dead animal, however recently killed; and those insects who simulate death when danger is near, escape the fangs of the ant-lion.

HYMENOPTERA.

GALL INSECTS.

Why are "apples" produced on oak-trees?

Because the female gall-fly lays her eggs in the buds, which consequently swell, and the excrescences serve for the abode of the larva until it has completed its changes, and is in a state to issue from its prison; after which the apples often become the residence of various kinds of wasps.

Why are oak-apples filled with fibres in the direction of the stem?