256 The Orders of Insects 



tained in them from those of the next sub-order 

 (Cyclorrhapha, p. 262). 



Group A. Nematocera. 



The Nematocera comprise those Diptera in which 

 the slender feelers have at least seven segments, and 

 usually many more : hence their name : '* Thread- 

 horns " (149, 150). 



Cecidomyidae. — The Cecidomyida or Gall-midges are a large family 

 of small slender flies. The head is relatively large, the compound 

 eyes lunate and not hairy, the simple eyes almost always absent. 

 The feelers have thirteen segments in the female and twenty-four at 

 least in the male ; the segments are bead-shaped, and bear long hairs 

 arranged in whorls. The mesoscutum shows no transverse suture. 

 The hind-body is elongate and has eight evident segments ; in the 

 male prominent claspers are present, and in the female a pointed 

 ovipositor. The legs are long, the haunches short, and the shins 

 without spines. The wings have never more than six longitudinal 

 nervures and hardly any cross-nervules ; the costal nervure is con- 

 tinued around a great part of the wing margin, and the wing area 

 is hairy or scaly. The larvse are fleshy, spindle-shaped maggots, 

 remarkable among insects in having fourteen segments behind the 

 small head ; between the first and second of these is a peculiar horny 

 process. The maggots live in plant tissues which usually become 

 deformed into various kinds of galls owing to the irritation set up 

 by the insects ; the obtect pups are enclosed in the dried larval skin. 

 The "Hessian-fly" {Cecidomyia destructor) so destructive to corn crops 

 is a well-known member of this family, which contains a multitude 

 of species distributed over the whole world. 



Mycetophilidae. — The MycetophHlda or FuNGUs-MiDGES are a very 

 large family nearly allied to the Cecidiomyidje, but distinguished by 

 the presence of simple eyes on the head, by the segments (ten to 

 sixteen in number) of the feelers being cylindrical, by the long 

 haunches, by the shins, clothed with stiff hairs and bearing spines 

 at the tip. The wing-neuration is simple ; there is usually but 

 a single cross-nervule linking the sub-costal nervure to the radial. 

 The larvae are elongate fleshy maggots living and feeding in vegetable 

 refuse or fungi ; they spin a cocoon in which the pupa rests. In 

 some genera the pupa has the prothoracic spiracles on raised pro- 

 cesses or horns. The Fungus-midges are exceedingly numerous, 

 and are world-wide in their range. 



Bibionidae. — The BiUonida are a family of moderately large flies 

 of somewhat stout build. The feelers are relatively much shorter 

 than in the preceding families, seldom longer than the head and 



