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THE INSECTS 



DlPTERA. 



The insects of the order Diptera are of great importance medically 

 in a variety of ways, either by the direct irritation of their bites, by their 

 transmitting disease directly, as does the common house fly typhoid 

 fever, or by acting as intermediate hosts for various parasites. They 

 are characterized by mouth parts formed for puncturing, sucking, or 

 licking. They present a complete metamorphosis, larva, pupa, and 

 imago. As a rule, the Diptera have a distinct pair of wings, the second 

 pair being rudimentary. With the Aphaniptera or Siphonaptera the 



FIG. 83. i and 2, male and female Xenopsylla cheopis. 3, Head of Cerato- 

 phyllus. 4 and 5, male and egg distended female of Sarcopsylla penetrans. 



wings are practically absent. Under the Aphaniptera, we have to 

 consider the Pulicidae or flea family. 



The order Diptera is usually divided into the following suborders: i. Orthorrha- 

 pha: Diptera with larvae having a differentiated head. The imago breaks through 

 the larval or pupal case by a T-shaped break and has no frontal lunule (an oval space 

 just above the root of the antennae). The Orthorrhapha are divided into: a. Nemo- 

 cera (with long, many jointed antennae) and b. Brachycera (with short antennae) 

 2. Cydorrhapha: larvae without differentiated head. The imago escapes through 

 an anterior opening and has a lunule and ptilinum (an inflatable projecting organ 



