598 THE MICROSCOPE. 



short and comparatively thick, with movements heavy and 

 ckimsy, and after shedding their skins become piipge : still 

 continuing to live in the water. The pupae differ from 

 the larvae principally in having four small scales on their 

 sides ; these conceal their future wings. While the Dragon- 

 fly continues in its aquatic state, both as larva and pupa, 

 it devours all the insects it can entrap ; and as it only 

 moves slowly, it is furnished with a very curious apparatus 

 near its head, which it projects at pleasure, and uses as 

 a trap. This apparatus consists of a pair of very large, 

 jointed, movable jaws, which the insect keeps closely 

 folded over its head, like a large mask, till it sees its 

 prey; when it does, it creeps softly along till it is suffi- 

 ciently near ; it then darts out those long, arm-like jaws, 

 and suddenly seizing its prey, conveys it to its mouth. 

 When the Dragon-fly is about to emerge from its pupa- 

 case, it places itself on the brink of the pond, or on the 

 leaf of some water-plant sufficiently strong to bear its 

 weight, and there divests itself of its pupa-case. When the 

 perfect insect first appears, it has two very small wings : 

 these gradually increase, and in a short time two other 

 wings appear. As soon as the wings are fully expanded, 

 and have attained their beautiful gauze-like texture, the 

 Dragon-fly begins to dart about, and then commences its 

 Avork of destruction. 



Equally rapid, exactly steered, and unwearied in its 

 flight is the Gnat. The wings of a Gnat have been calcu- 

 lated, during its flight, to vibrate 3,000 times in a minute ; 

 these wonderful wings are covered on surface and edge 

 v/ith a fine down or hair. The alternations of bright sun- 

 shine and rain, so commonly seen in March, are extremely 

 favourable to the appearance of Gnats. The first that 

 appear are called Winter Midges {Trichocera hyemalis). As 

 the spring advances, these Midges are succeeded by others 

 somewhat different ; and as the weather becomes warmer, 

 the true Gnats appear. The sting of the Gnat {Ctdex 

 pipiens) is well known ; although the insects themselves, 

 so very rapid in their movements, are so much dreaded 

 that very few people care to examine the delicacy and 

 elegance of their forms. The sting is very curiously con- 

 tri\ed (see fig. 269), and inclosed in. a sheath, folds up 



