r 



THE GNAT. 349 



part of the body is mucli thickened^ and exhibits the 

 different organs of the mature insect rather indi- 

 stinctly ; the posterior extremity is terminated by two 

 flat platesj which serve as natatory organs. 



Not less remarkable is the mode in which the final 

 metamorphosis takes place. The pupa^ floating at the 

 surface of the Avater^ swells out its anterior portion 

 until the skin bursts over the thoracic region^ and 

 from the slit thus formed the perfect Gnat soon begins 

 to emerge. This operation takes some little time, 

 but the greatest difficulty attends upon the liberation 

 of the first and second pairs of legs_, w hich are drawn 

 out of their cases by the elevation of the fore part of 

 the body into a perpendicular position, in which the 

 insect is of course exposed to considerable danger of 

 drowning by capsizing his frail boat. When this 

 object is effected, however, the remainder of the ope- 

 ration becomes easy ; the Gnat rests its free legs upon 

 the surface of the water, and supported by these and 

 the buoyancy of its half-empty pupa-skin, waits quietly 

 until its wings have acquired their proper consistence, 

 when it easily draws the rest of the body from its 

 case and rises into the air. 



Many other species of this tribe are very gnat-like 

 in their form and habits, except that they are innocent 

 of the crime of blood-sucking. Like the Gnats, some 

 of these are exceedingly fond of hovering in the air 

 and dancing up and down in immense swarms, fre- 

 quently intermixed with EphemercB, and their appear- 

 ance, when the rays of the setting smi fall upon their 

 gauzy wangs, is exceedingly beautiful. One of the 

 commonest and largest of these species is the Chiro- 

 nomus plumosus, the type of an immense genus, in- 

 cluding, according to Mr. Walker, upwards of two 



