DIPT ERA. 263 



TABANIDyE. 



In the Tabanidae we have the body very much short- 

 ened and the parts extremely concentrated. The pos- 

 terior portion of the metathorax, instead of being ex- 

 posed, as in the TipuUdae, or partially covered, as in 

 the Asilidae, is here entirely concealed by the basal 

 ring of the abdominal region, and is what we have 

 called a pseudo-sessile abdomen. The different spe- 

 cies of horse-flies belong to this family, represented by 

 the typical form of the order, Tabanus liiieola. 



CECIDOMYID/E. 



The gall-gnats constitute a large and aberrant fam- 

 ily. They produce the "pine cone" galls found on 

 willows, also the bushy tufts of leaves on golden-rod, 

 besides galls on the oak, hickory, and other trees. 

 The famous Hessian-fly, or wheat-midge, Cecidomyia 

 destructor, Say, belongs to this family. The Cecido- 

 myidae are of minute size and have few veins in their 

 wings, resembling in this respect the Hymenopterous 

 gall-insects (Cynipidse). The larvse do not have a 

 differentiated head, and the mouth parts have become 

 reduced in size, as the insects probably take little food 

 in the larval stage. The pupae of some species are 

 free, and others are covered with a puparium. In the 

 latter case the insect pushes itself out backward 

 through an opening in the puparium between the 

 seventh and eighth abdominal segments. 



