GNAT, a name (Anglo Saxon, gncrt) properly applied to the members of the Culieida; (a family of the insect order Diptera, division Orthorrhapha, subdivision iVematocera, section Encephala), but sometimes also used for the Chirono/nic1w. The Calicid(c consist of about 150 known species, of the genera Cselex, Anopheles, Aedes, Psorophora, Corethra, &c.; they are distributed over the chief divisions of the world, and, in spite of their very feeble build, reach as far north as man has penetrated (having been found during Nares's recent Arctic expedition). As regards time, examples of a Culer, and a Corethra have been discovered in the Tertiary beds of the Lower White River, Colorado. The Culicithe are distinguished from their immediate allies, amongst other characters, by having the parts of the mouth produced into a slender porrected rostrum, nearly half the length of the insect, and composed of many distinct pieces-(seven, according to Westwood, who remarks that the mouth in these delicate creatures is formed of the same number of pieces, and on the same plan, as that of the robust Tabani.), and many jointed palpi, very long and pilase in the male, in which sex the antenna are plumose and 14-jointed. The fibrils of the antenna are considered by Mayer as auditory organs. The usual special representative of the family is Culex pipiens, the common gnat, whose blood-sucking propensities have rendered it too well known. It pierces the skin with the needle-like lancets of its rostrum, which are barbed at the tips, and gradually inserts the whole of those organs, at the same time liquefying the blood by some fluid secretion, which apparently adds to the subsequent irritation. The female, recognizable by her more simple antennm and palpi, alone attacks man, and, in default of her favourite food, will feed on the honey of flowers. This blood-sucking taste is shared by the allied Sistuiiidce. The dreaded mosquito is nothing but a species of (vies, so closely allied to C. pipiens that it is difficult to say where " gnat " ends and "mosquito " begins, though the original mosquito is a native of Cuba. The curious humming noise (from which the name pipiens is fancifully derived) accompanying the flight of the gnat is caused by the extremely rapid motion of its wings, which have been calculated to vibrate 3000 times in a minute,-- the great relative bulk of the thoracic muscles accounting materially for this. In connexion with the gnat's wing it may be observed that, though apparently clear, " battledore scales have been discovered upon it by microscopists. The habit of gnats to associate in clouds has been frequently noticed, from the poet Spenser downwards ; and instances are even on record of their gatherings round church-spires having caused alarms of fire, from being mistaken for smoke. This apparently arises from the extreme spontaneity and ease of the individuals in their evolutions, which are so rapidly conducted as to enable them to fly unwet in a shower of rain. It has been observed that many of these large gatherings are exclusively composed of females. The traniiformations of the gnat have often been chronicled, and by none in a more interesting way than Reaumur, The female deposits her eggs in a little raft or boat-like mass, upon the surface of water, using her hind-legs while packing them together ; the larva; hatched from them are very active, diving in a jerky manner quickly, and often coining to the surface to breathe, suspending themselves head downwards, and taking in atmospheric air through a spiracle in one of the large tubes into which the end of the body subdivides. The pupa; are also capable of active motion by means of paddles at the tail, and also suspend themselves under the surface for respiratory purposes, though not breathing as in the larva, but through two little tubes on the back of the thorax. When the perfect insect makes its appearance, the pupa-skin is used by it as a floating foothold until it is ready to take to flight. So short a time is occupied by the entire series of metamorphosis that many generations are perfected in one summer.