ORDER DIPTERA: THE NEMATOCERA, ETC. 53 



these may be in tufts, or may be single branched or feathered 

 hairs ; sometimes the hairs are replaced by bristles, or 

 occasionally by spines. 



The abdomen, which is elongate and is the softest part 

 of the body, consists of 9 distinct segments. Sometimes 

 (particularly in the case of those jungle larvae that habitually 

 live in the drops of fluid that collect in holes in trees, in 

 leaves, in pitcher-plants and other such places, where they 

 are peculiarly liable to the attentions of insectivorous birds) 

 the whole abdomen is beset with tufts of stiff hairs like a 

 " woolly- bear" caterpillar; but more often the hairs are 

 restricted to or are only conspicuous at the sides of the 

 anterior segments and the free edge of the last segment. On 

 the dorsum of the 8th segment the breathing-organs open, 

 either by two independent orifices in a hollow at the base of 

 a papilla (as in the Anopheles group), or at the end of a 

 chitinous breathing-tube of varying length. The breathing- 

 tube, when present, has a valvular opening, and on its 

 under - surface are one or two rows of spines, the number 

 and form of which are specific. On the sides of the 

 8th segment also there are generally some scattered 

 scales. The 9th segment is the smallest, the intestine opens 

 at its free end, where there are also found bunches or 

 wisps of hair of extraordinary length, and four tapering 

 tracheal gills of varying size. 



The principal features of the internal structure are shown 

 in Fig. 12. The broad digestive tube passes straight through 

 the body, with glandular dilatations in the thorax, and 

 receives the five Malpighian vessels in the 6th abdominal 

 segment ; the two main tracheal trunks run dorsal of and 

 parallel with it, and end abruptly in the thorax at the point 

 where the air-openings of the pupa will subsequently appear. 



The larva progresses by energetic wriggling movements. 

 In repose some larvae hang head downwards, with the tip of 

 the breathing-tube at the surface of the water ; but the 

 larvae of the Anopheles group, and some others also, lie 

 horizontally at the surface. 



The larva feeds continuously and moults occasionally, and 

 in the most favourable circumstances of food and warmth 

 becomes full grown in little more than a week ; but cold 



