CULEX. 245 



near the end of its body with an organ which varies in length 

 according to the species, and forms an angle with the last segment 

 but one. The mouth of this organ is tunnel-shaped, and termi- 

 nates in five points, like a star ; and by this it is usually suspended 

 at the surface of the water, and preserves its communication with 

 the atmosphere. In its interior is a tube which is connected with 

 the trachea, and terminates in several openings at the mouth of 

 the organ. The points of the mouth, when the animal is disposed 

 to sink in the water, are used to close it, and cut off its commu- 

 nication with the atmosphere. When the animal is immersed, a 

 globule of air remains attached to the end of the tube, so that it 

 is in fact of less specific gravity than that element, and it is not 

 without some effort that it descends to the bottom ; but when it 

 wishes to rise again, it has only to unclose the tube, and it rises 

 without an effort to the surface, and remains suspended for any 

 length of time. Its anal extremity is clothed with bunches of 

 hairs, which are furnished with some repellent material which 

 prevents their becoming wet, and probably causes the dimple or 

 depression of the water round the mouth of the tube. When the 

 larva becomes a pupa, instead of a single respiratory appendage, 

 it is furnished with a pair, each in shape resembling a cornucopia, 

 and proceeding from the upper side of the thorax. By these tu- 

 bular horns it respires and is suspended at the surface." 



This genus, the Gnat or Mosquito, is too well known, from the 

 blood-sucking propensity of the female, to require any particular 

 notice. It is plentiful in all countries, whether arctic or tropical, 

 which abound in wood and water. The female lays about three 

 hundred eggs ; nearly a month intervenes between the egg-state 

 and the fly-state, and there are several successive generations in 

 one year. 



" Immense swarms of some species have occasionally appeared 

 in England, and at a distance have been mistaken for columns of 

 smoke. Gnats emit no sound when flying early in the spring, 

 before their thirst for blood is awakened. The warmer the wea- 

 ther, the greater is their thirst for blood, the more forcible their 

 flight, the motion of their wings more rapid, and the sound pro- 

 duced by that motion more intense." 



a. Tarsi with pale bands. 



b. Veins of the wings with five tufts of scales. Species 1. 



b b. Veins of the wings not tufted. Species 2-4. 

 a a. Tarsi without bands. 



b. Knees with white spots. Species 5. 



b b. Knees without spots. Species 6-9. 



