J 
DIPTERA.-(Flies.) 
By F. M. Howlett. 
The antennae moderately long and many-jointed, or quite short with 
few joints of which the last is thick and bears a bristle-like process. 
The mouth-parts for sucking, sometimes for piercing also. One pair 
of wings (mesothoracic), hyaline, with few cross-veins, occasionally 
hairy or scaly. A pair of metathoracic halteres. The body bristly, 
hairy, scaly, or bare. The metamorphosis complete; the pupa may 
be bare with the limbs free, or may be enclosed within the last larval 
skin. The length of the imaginal life is often greater than the larval, 
the latter frequently very short. None of the Diptera are very 
large, and many are very small. None are truly social. The larvae 
are without feet ; a large number are parasitic on insects and a few 
on mammals ; very many others are scavengers, while some are 
predators and herbivores; many are aquatic. The adults include 
very many flower-haunting species and some predators and blood¬ 
suckers. 
The Diptera are separated into two big groups corresponding to the 
way in which the pupa or pupa-case splits when the adult insect emerges. 
Those families in which there is 
a split more or less straight down 
the back of the thorax are group¬ 
ed together as ORTHORHAPHA 
(i.e., “ straightcrack ”), while those 
in which the split runs round 
the end of the pupa-case (fig. 
348) are called CYCLORHAPHA 
(i. e., “ roundcrack ”). 
Of course it is often impos¬ 
sible to see the way in which 
any particular fly escapes from 
the pupa, and these divisions would be useless were they not also 
indicated by other characters more easily observed. The Ortho- 
rhaphous pupa itself differs from the Cyclorhaphous in that the latter is 
enclosed in the last larval skin, which remains surrounding it as a 
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