358 DIPTERA. 



DIPTERA, 



FLIES may be easily recognized by their having but a single 

 pair of wings, the hinder pair being aborted, and existing in a 

 rudimentary state under the name of ''halter" The more es- 

 sential character of the Diptera, however, consists in the greatly 

 centralized, more or less globular thorax. Both the prothorax 

 and metathorax are greatly aborted, and the legs are somewhat 

 weak. As the second pair of wings are obsolete, the muscles 

 adapted for flying are not developed. 



When the wings are entirely wanting, as in Chionea, the 

 Spider fly, and the Spider-like Bat-tick (Nycteribia), the tho- 

 rax becomes still more globular, and the head of Nycteribia 

 shows a tendency to become immersed in the thorax, as in the 

 spiders. 



The abdomen is either short, conical and broad at the base, 

 being rarely pedicellate ; or long and cylindrical, or flattened 

 either horizontally or laterally. The conical form of the abdo- 

 men accords with the quick jerky flight of the House fly, as 

 compared with the steady slow flight of Tipula, whose abdomen 

 is very long. The abdomen is composed of from five to nine 

 distinct segments. As Lacaze-Duthiers states, the Diptera as 

 a rule have no true ovipositor like that of bees, etc. , though the 

 three terminal rings are retracted within the abdominal cavity, 

 and are capable of being thrust out like the joints of a telescope. 

 When about to lay their eggs they simply place them in cracks 

 or upon the substances that are to form the future food of the 

 larva, having no organs for boring, though the female Tipulids 

 are able to work the hard tip of the abdomen into the ground 

 where they deposit their eggs. The terminal ring of the abdo- 

 men in the males is provided with clasping organs. 



The head is very free from the thorax in the true flies, and 

 is spherical, hemispherical or conical. The eyes are large, with 

 very numerous facets, and often approach each other closely on 

 the front of the head, especially in the males. The ocelli, when 

 present, are placed on the vertex, and the antennae are in- 

 serted below, in the middle (antero-posteriorly) of the front. 



