in mechanics, a crois with leaden weights at its ends; or rather, a heavy wheel at right angles to the axis of a windlass, jack, or the like; by means of which, the force of the power, whatever it is, is not only preserved, but equally distributed in all parts of the revolution of the machine. See MECHANICS.

FLIES FOR FISHING. See FISHING-FLY.

Vegetable Fly, a very curious natural production chiefly found in the West Indies. "Excepting that it has no wings, it resembles the drone both in size and colour more than any other British insect. In the month of May it buries itself in the earth, and begins to vegetate. By the latter end of July the tree is arrived at its full growth, and resembles a coral branch; and is about three inches high, and bears several little pods, which dropping off become worms, and from thence flies, like the British caterpillar."

Such was the account originally given of this extraordinary production. But several boxes of these flies having been sent to Dr Hill for examination, his report was this: "There is in Martinique a fungus of the clavaria kind, different in species from those hitherto known. It produces sobs from its sides, I call it therefore clavaria sobolifera. It grows on putrid animal bodies, as our fungus ex pede equino from the dead horse's hoof.

"The cicada is common in Martinique, and in its nympha state, in which the old authors call it tettigometra: it buries itself under dead leaves to wait its change; and, when the season is unfavourable, many perish. The seeds of the clavaria find a proper bed on this dead insect, and grow.

"The tettigometra is among the cicadae in the British museum; the clavaria is just now known.

"This is the fact, and all the fact; though the untaught inhabitants suppose a fly to vegetate, and though there is a Spanish drawing of the plant's growing into a trifoliate tree, and it has been figured with the creature flying with this tree upon its back."

The ingenious Mr Edwards has taken notice of this extraordinary production in his Gleanings of Natural History, from which the figures on Plate CV are taken.

FLY-Boat, or Flight, a large flat-bottomed Dutch vessel, whose burden is generally from 400 to 600 tons. It is distinguished by a stern remarkably high, resembling a Gothic turret, and by very broad buttocks below.

FLY-Catcher, in zoology. See MUSCICAPA.

FLY-Trap, in botany, a newly discovered sensitive plant. See Dionaea Muscipula.

FLY-TREE, in natural history, a name given by the common people of America to a tree, whose leaves, they say, at a certain time of the year produce flies. On examining these leaves about the middle of summer, the time at which the flies used to be produced, there are found on them a sort of bags of a tough matter, of about the size of a silbert, and of a dusky greenish colour. On opening one of these bags with a knife, there is usually found a single full-grown fly, of the gnat kind, and a number of small worms, which in a day or two more have wings and flee away in the form of their parent. The tree is of the mulberry kind, and its leaves are usually very largely stocked with these insect-bags; and the generality of them are found to contain the insects in their worm-state; when they become winged, they soon make their way out. The bags begin to appear when the leaves are young, and afterwards grow with them; but they never rumple the leaf, or injure its shape. They are of the kind of leaf-galls, and partake in all respects, except... except size, of a species we have frequent on the large maple, or, as it is called, the sycamore.

The fly-tree is found in many parts of France, where it grows in great abundance, and is there said to bear fruit which give origin to a vast number of flies. The truth of the matter is this. The tree is a species of turpentine tree, and frequently produces or gives origin to certain tubercles, which, in the common turpentine tree, are called its horns. There are a fort of long bladders, of the length and thickness of a finger; which arise, not from the stalks, as fruits do, but from the surface of the leaves, and are only a kind of leaf-galls formed of an elongation of its outer membranes, occasioned by the punctures of a number of insects contained within it, which occasion a derivation of fresh juices to the part. These insects are not flies of the common kind, but are the puceros so well known for feeding on the leaves and tender stalks of trees; and some few of these only are winged, the others being destitute of them.—The origin of these tubercles or bladders is this. The female pucerons, as soon as produced from the parent, makes a way under the membrane that covers the leaf, by means of a hole bored in it with the trunk. This hole soon heals up after she is in; and the young ones, which she afterwards produces, by their wounding and sucking the sides of the lodgment in which they find themselves placed, occasion all the swelling and growth of the tubercle.