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CHAPTER Ii. 
DIPTERA. 
Mosquitoes, Gnats, Flies, and Ticks. 
The insects of this group are readily distinguished by their having 
only one pair of wings, the second pair, common to other insects, being 
represented by a pair of rudiments or modified structures called 
halteres or balancers. In many of the parasitic forms, however, the 
wings are entirely wanting, as in the sheep-tick, spider-fly, ete. They 
have suctorial mouthparts, and, in the forms attacking the various 
animals, these parts become readily adapted to penetrating the skin to 
reach the small bloodvessels. 
The larve are fleshy grubs or maggots, or slender worms, adapted in 
the different families to widely different conditions of existence, but in 
nearly all cases requiring some degree of moisture. In this respect 
they range all the way from the entirely aquatic mosquito larve to the 
forms which mature in comparatively dry situations in earth or even 
upon plants. 
The pup are in some cases formed by the simple contraction and 
hardening of the larval skin and in disclosing the imago may either 
split on the dorsal surface or in a circular manner so that a eap is 
separated from the head end, leaving a round aperture through which 
the adult emerges. 
While comparatively few are parasites in the strictest sense, the 
group includes many of the most troublesome of the insect enemies of 
live stock, as will be recognized in the discussion of particular species. 
Family CULICID™®. 
(Mosquitoes, Gnats, etc.) 
The members of this family are slender-bodied, delicate insects with 
gauzy wings, the veins of which bear minute scales. The mouth parts 
are provided with lancet-like piercing mandibles which, in the females, 
are capable of inflicting a severe bite. 
The larve in those species whose life history has been traced are 
aquatic, and this may doubtless be considered as the usual habit for 
the family; but it is very probable that many species pass through 
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