MOSQUITOES, MIDGES AND FLIES. 331 



sheep, horses, etc. Dipterous maggots breathe in 

 two ways. Some have the lateral spiracles — along 

 the sides of the body ; while others, such as maggots 

 of blow flies, fruit flies, have a pair of spiracles 

 at the head and a pair of plates at the tail end of 

 the body, with three spiracles on each plate. (Plate 

 44, Fig. 4 a.) 



Many dipterous larvae live in mud or in shallow 

 water, and some of these have an elongation of the 

 posterior end of the body to form a tube (Plate 43, 

 Fig 4 a) which leads to the air, and which enables 

 such maggots to get a sufficient amount of air, for 

 in mud the supply is limited. 



In warm weather maggots develop very quickly ; 

 indeed, the life history of the house fly from the 

 egg to the adult may be but a fortnight. Their 

 rapid development means an enormous increase, 

 and this makes some types very serious pests. 



Though maggots are repulsive to us, associating 

 them as we readily do to the ''blowing" of meat 

 in hot weather, attacking sheep, etc., yet they arc 

 scavengers which rid us of much disease-carrying 

 matter. 



The pupa (Plate 40,. Fig. 3) is interesting, for 

 in many cases the last larval skin is used as a kind of 

 cocoon, within which the larva pupates, so that in 

 these cases the adult emerges first from its own pupal 

 skin and then has to break through the ' ' puparium ' ' 

 or last larval skin. The puparium is in two forms : 

 (a) When the appearance of larval form is retained 

 —example, soldier flies (Plate 40, Fig. 8) and in 

 the ''hairy maggot" of the sheep fly the larval 



