252 



The Orders of Insects 



end in two claws and a well-formed two or three- 

 lobed pad. The wings are membranous, with not 

 more than seven longitudinal nervures, a sub-costal 

 (two sometimes), a radial, an ulnar, ^ two medians, and 

 two anals j the forking and bending of these nervures, 

 and the presence of a variable number of cross 

 nervules lead to the formation on the wing area 

 of cells, which are never very numerous. A small 

 rounded part of the anal area at the base of the wing 

 is often sharply marked off. 

 Behind the wings a pair of 

 scales — small membranous 

 plates — are present in some 

 families. The hind-body may 

 possess eight evident segments, 

 but in some families only four 

 or five are visible ; prominent 

 male claspers are present in 

 some groups, and the ovipositor 

 of the female often consists of 

 the reduced and retractile 

 hinder abdominal segments 

 (fig. 141) (4, 150, 151). 

 Fig. i4i.-ovipositor of Warble- Develooment, and 



ny {Hypoderma bovis-, D. __ ... t-., t~v 



G.). a. from side; b. tip HaDltS. 1 he JJiptera paSS 



&RiieTinsectLfff;o1: through a Complete metamor- 

 2 (U..S. Dept. Agr.). phosis ; the larva is in all cases 



cruciform, a grub or maggot destitute of true legs, 

 though prolegs and other secondary organs of loco- 

 motion are often present. In many families the larvye 

 are aquatic. The pupa (fig. 142) is sometimes free, 

 but usually incomplete or obtect, though the cohesion 

 of the appendages is less marked than in the pupae 



1 Many systematic writers on the Diptera call the third nervure 

 (ulnar) the cubital ; it is really a branch of the radial. The lower 

 median is probably the true cubital. 



