CULEX. 9> 



small larvae of the gnat, with their tails at the 

 surface, and their heads beneath. These ani- 

 mals are very lively, and precipitate themselves 

 to the bottom by the help of their little fins the 

 moment they are approached. They return 

 ao-ain, however, to their former position as soon 

 as possible, on account of the organ of respi- 

 ration, which is placed near the tail ; and which 

 is not calculated, like the gills of fish, to extract 

 air from the water. When the larva becomes 

 a chrysalis, this organ is multiplied, and its place 

 is changed. Instead of one air-tube near the 

 tail, we now find two upon the thorax, erect, 

 like ears, with their open ends always above 

 the surface of the water ; the body at the same 

 time is curled round, with the tail beneath the 

 breast. In about ten days after becoming a 

 chrysalis, the gnat prepares for its last trans- 

 formation ; the upper part of the body swells, 

 the skin cracks, and the head of the insect ap- 

 pears above the surface of the water : the 

 other parts by degrees follow through the same 

 opening, till nothing is left behind but the tail. 

 The gnat, during this operation, raises itself per- 



