We will select among these parasites some two-winged insects, among which there are many which suck blood. Those which are generally called flies are divided into two groups, under the name of _Nemocera_ and _Brachycera_; many of these live only on blood, and are more terrible than the lion and the tiger; in many countries man can defend himself against those fierce carnivora, but he is there completely powerless and without defence against these insects. [Illustration: Fig. 7.--Antenna of a Gnat.] Among the Nemocera are found the gnats (_Culex_ _pipiens_), those 116 brilliant children of the air, with fine and slender claws, and delicate membranaceous wings, and wearing on their heads feathery antennæ of rare elegance. They are known in the Old as well as in the New World, and in southern regions it is necessary to guard against their nightly attacks by musquito curtains. In the Antilles they bear the name of _Maringouins_, and in hot countries they are generally known as musquitoes. They are also called gnats, midges, black-flies, zanzare, &c., in different localities, but as may be supposed, these names do not always designate the same insect. The musquitoes of the French colonies are often _Simulia_. At Madagascar and the Isle of France is found the gnat known by the name of _Bigaye_. In Davis's Straits, in lat. 72° N., Dr. Bessels, on board the _Polaris_, was obliged to interrupt his observations on account of these insects. A great number of them have been seen up to the 81st degree of latitude. Besides gnats, there were also found _Chironomi_, _Corethræ_, and _Trichoceræ_. As Dr. Bessels was able to save from the _Polaris_ some small collections of insects, we shall soon know the names of the species which live in these high latitudes. It is said that the Esquimaux and the Lapps cover their skin with a coating of grease, not only to lessen the effect of the cold, but to defend themselves from the stings of gnats. "The gnat is a plague from June till the first frosts," says Mons. Thoulet, speaking of his abode among the Chippeways. "It renders the country almost uninhabitable; and one is so exhausted by this suffering, which does not cease by night or by day, and by the loss of blood through their bites, that we manage to get through our daily 117 task only by the force of habit; we can neither speak nor think. When the musquitoes disappear, the 'black-flies' come: the musquito pumps up a drop of blood and flies away; the black-fly bites and makes a wound which continues to bleed." De Saussure has alluded to curious relations which exist in Mexico between a bird, a beast, and an insect. "Bulls bury themselves in the mud," says this learned traveller, "in order to avoid the attacks of gnats, leaving in the air only the tip of their nostrils, on which a beautiful bird, the Commander, posts himself, in this position the Commander watches for the _Maringouin_ which is bold enough to enter the nostrils of the animal."