124. Human Physiology. 



with glittering wings and a long proboscis. Almost in the 

 same manner is born the gorgeous dragon fly. In the water ; 

 its pupa moves itself by a hydraulic engine. When this phase 

 of its life is completed it climbs upon a stalk, and by some 

 hooks, provided for the purpose, hangs itself up to dry. In a 

 little while its skin cracks open and the perfect insect comes 

 out, its four great wings perfectly formed, only folded up 

 carefully, like leaves or petals of flowers; these are spread out, 

 dry in the sun, and then it flies off glittering with its splendid 

 beauty one of the most powerful and perfect of insects 

 flying backward, as well as forward, and even sideways with 

 the greatest rapidity. 



The wasp fly is also born in the water, and its larva is 

 provided with a long breathing tube which rises to the surface 

 and furnishes it with air. Some flies have the providential 

 instinct to lay their eggs in the bodies of dead animals, which 

 their larvae, brought forth in immense numbers, devour, before 

 they can fill the air with pestilential odours; and the progeny of 

 a single fly consume more than a lion. Another fly lays its 

 eggs on the hairs of living animals that they may be licked off, 

 swallowed, and hatched in its bowels. The lace- wing fly hangs 

 its eggs to the leaves of plants so as to produce the most 

 delicate fringes. 



These flies, when carefully examined, are found to have, 

 in every way, the most remarkably constructed organs. They 

 have feet with which they can walk up panes of glass, or upon 

 the ceiling of a room ; they eat loaf sugar by first dissolving it 

 with their saliva, and then sucking it up with their trunks. 

 The air-pipe of a fly is made of a special elastic thread between 

 two membranes the perfection of a mechanical contrivance 

 combining strength, lightness, and elasticity. The wings of the 

 fly are of the same character, and are moved by a nervous and 

 muscular apparatus even more wonderful. The common 

 house-fly moves its wings at the rate of 600 strokes in a 



