90 OUTLINES OF ENTOMOLOGY. 



larly distinguished as flies. Although many flies, in the larva state, are 

 undoubtedly useful as scavengers, yet the perfect insects are, most of 

 them, 8o annoying, and often so positively injurious, that the entire 

 Order is regarded with much disfavor. Mosquitos, gnats, house-flies, 

 gad-flies and other species frequently occur in such immense swarms 

 in certain localities as to render life'almost intolerable. A few species 

 are brilliantly colored, or of striking size or form, but, as a rule, the 

 members of this division are the most individually inconspicuous of 

 insects. 



The bodies of most flies are soft and fragile. The head is usually 

 larg(3, round or hemispherical, often quite concave behind, and is at- 

 tached to the thorax by a peg-like neck, on which it can be twirled 

 almost completely around without being separated from the body. The 

 eyes are, except in a few very lowly organized species, very large, cov- 

 ering the greater part of the head, and their faceted structure can be 

 seen even without the aid of a lens. The mouth-parts are very differ- 

 ently developed in the different families, but are all peculiarly fitted for 

 sipping fluids. In the house-fly the jaws and true maxillae are wanting, 

 but the secondary maxillee and the lower lip form a proboscis which 

 ends in a pair of broad flaps, whose ridged surface enables the insect 

 to lap up sweet fluids or the perspiration from the hand, or the juices 

 of meat or other liquids to which it is attracted. When not in use, the 

 proboscis being jointed, is folded up ^d tits into a groove in the face. 

 The so-called "stinging tlies" have the jaws modified into very sharp 

 lancets, which are so strong that they are capable of piercing even the 

 thick skin of a horse and drawing the blood. The antennte are either 

 short and stout, having but three joints and a bristle, or are many- 

 jointed, long and feathered, as in the mosquito. The thorax is large 

 and round, the first and third segments — pro-thorax and meta-thorax — 

 being very small and closely consolidated above with the meso-thorax, 

 which is large and muscular. The wings are composed of thin, trans- 

 parent or smoky membrane supported by strong veins. They can be 

 vibrated with exceeding swiftness, and the insects are capable of longer 

 and more continuous flights than a»y of the four-winged species. At 

 the base of each wing is a little roundish scale called the icinglet or 

 alulet, the use of which has not yet been discovered. The hind wings 

 are represented by two thread-like organs ending in little knobs, which 

 are the halter es, poisers or balancers, whosfe function is likewise un- 

 known. The legs are generally rather weak and slender, and in some 

 species are very long. The feet are five-jointed, and besides the claws, 

 are provided with a bilobed cushion clothed with microscopic hairs 



