THE WATER GNAT. 255 



upper cluster of compound eyes occupies the same 

 position as the eyes of the fish, the lower clusters will 

 be placed at the angles of the lower jaw, just at their 

 junction with the upper jaw. Thus the insect is 

 specially fitted for its water-trespassing life, by pos- 

 sessing one set of eyes for the water and a second for 

 the air. 



At the bottom of the illustration, and occupying 

 the middle, is seen a creature which has some resem- 

 blance to a centipede. This is the larva of the Whirl- 

 wig, and the projections from the side are the gills 

 or branchiae, as they are scientifically termed. This 

 larva is always in motion, so as to make the water 

 impinge against the gills. Generally, it does so by 

 means of a graceful serpentine curve, in which the 

 white gills stream about like white plumes waving in 

 the wind. Sometimes it will wriggle its way upwards 

 for several inches, and then sink to the bottom, the 

 gills being stretched out on either side of the body, 

 and helping to support it. 



These larvse are much eaten by the water scorpion, 

 who finds plenty of nourishment in their fat, soft 

 bodies. 



THE WATER GNAT (Gems IdCUstris). 



Again I take a single species as a type of several 

 others the insect which is represented as walking on 

 the surface of the water. There are many insects be- 

 longing to the Heteroptera, which are grouped together 

 under the general and appropriate name of Hydro- 

 metridaa, or Water Measurers. They all have slight 



