DIPTERA OK TRUE FLIES. '219 



may not oast off the larval skin. The naked pupje,(fig. 117) 

 are very varied, often armed with spines and bristles (fig. 

 124, 5). Those that retain the larval 'skin as a case form 

 so-called " puparia," the true pupa heing found in the brown 

 case, formed of the maggot's old skin much hardened (fig. 

 65, A, i. and ii.). 



Diptera are divided into two large sections, the Orthorrhapha 

 and the Oydorrhapha. The first have their larvae with a dis- 

 tinct chitinous head, and their pup£e escape from the larval skin 

 by a T-shaped rent ; the second have no chitinous head, and 

 the pupa or imago escapes from the larval skin by a circular 

 opening. 



There are two divisions in the Orthorrhapha — the Nema- 

 tocera and the Brachyeera, — the former with thread-like many- 

 jointed antennae, the latter with antennae composed of two or 

 three large basal joints with a multiarticulate bristle (fig. 145, a). 

 Lastly, there are the Pupipara, which produce their young in a 

 fully matured state as puparia. 



There are many flies extremely harmful to the agriculturist 

 and gardener. Some carry diseases from man to man and 

 animal to animal (Mosquitoes and Malaria, Tsetse flies and 

 Sleeping Sickness). 



Cecidomyidae, or Gall-G-nats. 



This family contains only small flies, some of which are 

 distinctly harmful, such as the Hessian Fly {Cecidomyia de- 

 structor), the Wheat Midge (Diplosis tritici), and the Pear 

 Midge {Diplosis pyrivora). The Cecids have very few veins in 

 their wings, hairy antennae, and often hairy wings. The larvae 

 are sometimes white, at others red in hue, and composed of 

 fourteen segments. They always have on the under surface, 

 close to the anterior extremity, a curious process called the 

 Breast Bone or Anchor Process (fig. 118). Many larvae form 

 galls, in which they live, and may or may not pupate there. 



