GNATS 



the anterior end upwards and the tail directed downwards. The 

 thorax is at this stage very large and rounded, and is placed 

 nearest to the water surface ; the head being bent down ventrally 

 and the abdomen hanging, not straight, but bent under the 

 thorax. From the top of the thorax project upwards two 

 respiratory trumpets or " horns " which, in the resting position, 

 open through the surface to the air. Just inside the lips of the 

 trumpets lie numerous fine hairs, which prevent the entrance of 

 water when the animal 

 dives. Fastened down 

 against the sides of the 

 thorax are the large flat 

 wings, and behind them 

 small triangular plates, 

 representing and contain- 

 ing the halteres. The an- 

 tennae, eyes, and legs are 

 all visible on the ventral 

 surface of the enlarged an- 

 terior region, and within 

 them can be seen the 

 corresponding organs of 

 the adult. The abdomen 

 has a few bristles on its 

 dorsal surface, and at the 

 end of its last undoubted 

 segment, the eighth, a pair 

 of large fins, beneath which 

 is a small projection bearing two blunt processes directed back- 

 wards. This represents the ninth and tenth segments. The 

 terminal fin is a powerful swimming organ, and is employed in 

 a manner that recalls the tail-fin and telson of a crayfish or shrimp ; 

 for by rapidly flexing the abdomen the pupa is -able to dart 

 rapidly through the water, the first stroke of necessity drawing 

 the animal away from the surface. Subsequent strokes cause 

 erratic darts in the depths, but very soon the pupa floats up to 

 the surface again, owing to the presence of a large air-space within 

 the upper part of the thorax. Pupae exhibit a preference for 



FlG. 12. A, pupa of culex ; B, one of the 

 respiratory tubes. 



