THE COMMON GNAT. 443 



The last segment of the abdomen terminates in a 

 kind of flat fin, by means of which the creature 

 obtains its motion in the water. 



THE COMMON GNAT*. 



Few insects are better known than this species 

 of Gnat, and there are not many that afford a more 

 interesting history. 



From the beginning of May their larva? may be 

 seen in the stagnant waters, with their heads down- 

 ward, and the extremity of their abdomen at the 

 surface; from the side of which arises the hollow 

 tube through which they respire. Their heads are 

 armed with hooks, that serve to seize on insects and 

 bits of grass on which they feed ; and on their sides 

 are four small fins, by the help of which they swim 

 and crawl along. These larva? retain their form 

 during a fortnight or three weeks, after which they 

 turn into chrysalids ; and all the parts of the winged 

 insect are now distinguishable through their thin 

 exterior covering. The situation and shape of their 

 respiratory tube is also altered : this is now divided 

 into two parts, and is placed near the head. The 

 chrysalids abstain from eating, and reside almost 

 constantly at the surface of the water ; but, on the 

 least motion, they may be seen to unroll themselves 

 from their spiral position, and, by means of little 

 paddles on their hinder part, to plunge to the bot- 

 tom. In the course of a few days they are trans- 



* Culsx pipiens. Linn, 



