where it is somewhat enlarged and angular, and on both sides finely indented with teeth. A more minute examination of the sheath demonstrates that it is composed of two horny pieces slightly curved, and ending in the form of an elongated spoon, the concave part of which is adapted to receive the convex end of the ovipositor.

When the protruded instrument is further examined with a microscope, the denticulations, nine in number on each side, appear strong, and arranged with great symmetry, increasing in fineness towards the point, where there are three or four very small ones, beside the nine that are more obvious. The magnifier also shews that the instrument itself, which appeared simple to the naked eye, is in fact composed of three different pieces, two exterior armed with the teeth before mentioned, denominated by Réaumur files (limes), and another pointed like a lancet, and not denticulated. The denticulated pieces moreover are capable of being moved forwards and backwards, while the centre one remains stationary, and as this motion is effected by pressing a pin or the blade of a knife over the muscles on either side at the origin of the ovipositor, it may be presumed that those muscles are destined for producing similar movements when the insect requires them. By means of a finely pointed pin carefully introduced between the pieces, and pushed very gently downwards, they may be, with no great difficulty, separated in their whole ex

tent.

The contrivance by which those three pieces are held united, while at the same time the two files can be easily put in motion, are similar to some of our own mechanical inventions, with this difference, that no human workman could construct an instrument of this description so small, fine, exquisitely polished, and fitting so exactly. We should have been apt to

form the grooves in the central piece, whereas they are scooped out in the handles of the files, and play upon two projecting ridges in the central piece, by which means this is rendered stronger. M. Réaumur discovered that the best manner of shewing the play of this extraordinary instrument is to cut it off with a pair of scissors near its origin, and then, taking it between the thumb and the finger at the point of section, work it gently to put the files in motion.

Ovipositors, with files, of Tree-hopper, magnified.

Beside the muscles necessary for the movement of the files, the handle of each is terminated by a curve of the same hard horny substance as itself, which not only furnishes the muscles with a sort of lever, but serves to press, as with a spring, the two files close to the central piece, as is shewn in the lower figure.

M. Pontedera, who studied the economy of the tree-hoppers with some care, was anxious to see the

insect itself make use of the ovipositor in forming grooves in wood, but found that it was so shy and easily alarmed, that it took to flight whenever he approached; a circumstance of which Réaumur takes advantage, to soothe his regret that the insects were not indigenous in his neighbourhood. But of their workmanship when completed, he had several specimens sent to him from Provence and Languedoc by the Marquis de Caumont.

The gall-flies, when about to deposit their eggs, select growing plants and trees; but the tree-hoppers, on the contrary, make choice of dead, dried branches, for the mother seems to be aware that moisture would injure her progeny. The branch, commonly a small one, in which eggs have been deposited, may be recognized by being covered with little oblong elevations caused by small splinters of the wood, detached at one end, but left fixed at the other by the insect. These elevations are for the most part in a line, rarely in a double line, nearly at equal distances from each other, and form a lid to a cavity in the wood about four lines in length, containing from

Excavations for eggs of Tree-hopper, with lids raised.

four to ten eggs. It is to be remarked, that the insect always selects a branch of such dimensions, that it can get at the pith, not because the pith is more easily bored, for it does not penetrate into it at all, but to form a warm and safe bed for the eggs. M. Pontedera says, that when the eggs have been deposited, the insect closes the mouth of the hole with a gum capable of protecting them from the weather; but M. Réaumur thinks this only a fancy, as

out of a great number which he examined, he could discover nothing of the kind. Neither is such a protection wanted; for the woody splinters above mentioned furnish a very good covering.

The grubs hatched from these eggs (of which, M. Pontedera says, one female will deposit from five to seven hundred) issue from the same holes through which the eggs have been introduced, and betake themselves to the ground to feed on the roots of plants. They are not transformed into chrysalides, but into active nymphs, remarkable for their fore limbs, which are thick, strong, and furnished with prongs for digging; and when we are told by Dr. Le Fevre, that they make their way easily into hard stiff clay, to the depth of two or three feet, we perceive how necessary to them such a conformation must be.

SAW-FLIES.

An instrument for cutting grooves in wood, still more ingeniously contrived than that of the treehopper, was first observed by Vallisnieri, an eminent Italian naturalist, in a four-winged fly, most appropriately denominated by M. Réaumur the saw-fly (Tenthredo), of which many sorts are indigenous to Great Britain. The grubs from which those flies originate are indeed but too well known, as they frequently strip our rose, gooseberry, raspberry, and red currant trees of their leaves, and are no less destructive to birch, alder, and willows; while turnips and wheat suffer still more seriously by their ravages. These grubs may readily be distinguished from the caterpillars of moths and butterflies, by having from sixteen to twenty-eight feet, by which they usually hang to the leaf they feed on, while they coil up the hinder part of their body in a spiral ring. The perfect flies are distinguished by four transparent wings; and

some of the most common have a flat body of a yellow or orange colour, while the head and shoulders are black.

In order to see the ovipositor to which we shall for the present turn our chief attention, a female sawfly must be taken, and her belly gently pressed, when a narrow slit will be observed to open at some distance from the anus, and a short, pointed, and somewhat curved body, of a brown colour and horny substance, will be protruded. The curved plates which form the sides of the slit, are the termination of the sheath, in which the instrument lies concealed till it is wanted by the insect. The appearance of this instrument, however, and its singular structure, cannot be well understood without the aid of a microscope.

α

a, Ovipositor of Saw-fly, protruded from its Sheath, magnified.

The instrument thus brought into view, is a very finely contrived saw, made of horn, and adapted for penetrating branches and other parts of plants where the eggs are to be deposited. The ovipositor-saw of the insect is much more complicated than any of those employed by our carpenters. The teeth of our saws are formed in a line, but in such a manner as to cut in two lines parallel to, and at a small distance from each other. This is effected by slightly bending the points of the alternate teeth right and left, so that one half of the whole teeth