GORDIUS, the HAIR-WORM, a genus of insects belonging to the class of vermes intestina. There are several species, 1. The aquaticus, or water hair-worm, is 10 or 12 inches in length, and of about the thickness of a horse hair: its skin is smooth and somewhat glossy, without furrows; its colour pale yellowish white all over, except the head and tail, which are black and glossy. The body is rounded, and very slender in proportion to its length: the mouth is small, and placed horizontally; the jaws are both of the same length, and obtuse at their extremities. This species is common in our fresh waters, more especially in clay, through which it passes as a fish does through the water, and is the author of many springs. This is the worm that in Guinea and in some other of the hot countries gets into the flesh of the natives, and occasions great mischief; with us, though frequent enough in water where people bathe, it never attempts this.—2. The argillaceus, or clay hair-worm, is only a variation of the preceding one in colour, being yellowish at the extremities. It chiefly inhabits the clay; and Linnaeus calls that its proper element, from its being generally dug out of it.—3. The medinenfis, or muscular hair-worm, is all over of a pale yellowish colour. It is a native of both Indies; frequent in the morning dew, from whence it enters the naked feet of the slaves, and occasions a disease much known in those countries, and to which children are very liable: it creates the most troublesome itchings, and too often excites a fever and inflammation. It particularly infests the muscles of the arms and legs, from whence it may be drawn out by means of a piece of silk or thread tied round the head: but the greatest caution is necessary in this simple operation, lest the animal, by being strained too much, should break; for if any part remains under the skin, it quickly grows with redoubled vigour, and becomes a cruel, and sometimes fatal enemy, to the poor slaves in particular. Baths with infusions of bitter plants, and all vermifuges, destroy it.—4. The marinus, or sea hair-worm, is filiform, twisted spirally, and lying flat, about half an inch in length; of a whitish colour, smooth, and scarcely diminishing at the head. It is as great a tormentor of herrings, bleaks, and various other fish, as the gordius medinenfis is of man. The fish when infested with these animals rise to the surface, and tumble about as if in great agony.