ORDER VII.- TWO-WINGED INSECTS, OR FLIES. 319 



in the garden or yard during the summer, it will in a few 

 weeks be entirely populated with the larvae of mosquitoes ; 

 for each female deposits about three hundred eggs, which, 

 in three or four weeks after, are metamorphosed into per- 

 fect flies, which again deposit new eggs, and so on until six 

 or seven generations take place in one season. Their im- 

 mense number would give us much trouble in every section 

 of the country were they not the favorite food of many 

 birds, particularly of the swallows, as well as of dragon- 

 flies and other insects, who diminish their number and help 

 to rid us of their troublesome company. 



Their eggs are of an oval form, and, perpendicularly glued 

 together in masses, swim upon the water like rafts, about 

 three lines long. They are at first white, but become green 

 after a few hours, and afterward gray. After two days the 

 larvas come out, and swim around with the greatest rapid- 

 ity, very often coming to the surface of the water to breathe, 

 their respiratory organ being situated at the extremity of 

 the hind body. In two weeks they change into a pupa, 

 which still remains upon the surface of the water, and 

 after a week bursts open, and the perfect mosquito flies out 

 as if shot from underneath the water. 



THE END. 



