INSECT A. 197 



number of featliered pieces, which radiate from tlie body like the 

 stems of a fan. i^fig' 97.) 



The Insects which have the anterior pair of wings in the condition 

 of the heraelytra, form the order Hem iptera; butcertain genera have the 



dense part of the anterior wings 

 reduced to so small a strip, that 

 they are scarcely distinguishablcj 

 except by size, from the pos- 

 terior pair, and these insects 

 constitute a section of the order 

 termed Homoptera. 



A few remarkable genera of 

 insects have the anterior pair of 

 wings reduced to small or rudimental elytra, and the posterior pair 

 unusually large, and folded longitudinally, like a fan when at rest. 

 The anterior wings being reduced to minute appendages twisted 

 spirally, the Order has been hence termed Strepsiptera, The species, 

 in their larval state, are parasitic on the bee tribe. 



The order Diptera is characterised by the development of the an- 

 terior pair of wings into organs of flight, and the retention of the 

 hinder pair in the condition of minute clavate appendages, usually 

 called the "balancers." The prothorax and metathorax are rudi- 

 mental w^hilst the mesothorax is disproportionately large to form the 

 required space for the powerful muscles, which execute, through the 

 two anterior wings, the function of flight. 



In almost every Order of Insects there are species, or there are 

 individuals, as the females of particular species, which are apterous ; 

 but since the time of Aristotle, who divided insects primarily into the 

 " winged," Ptilota, and the " wingless," Aptera, most of the hexapod 

 insects devoid of wings have been artificially grouped together. Cu- 

 vier and Latreille divide the Apterous Insects into three tribes, the 

 Suctoria (fleas), the Parasita (lice, including the Pediculus capitis 

 and Pthirus inguinalis of the human species), and the Thysanoura, 

 including the Lepisma and Podura or skip-tails. 



The grand and characteristic endowment of an insect is its wings ; 

 every part of the organisation is modified in subserviency to the full 

 fruition of these instruments of motion. In no other part of the 

 Animal Kingdom is the organisation for flight so perfect, so apt to 

 that end, as in the class of insects. The swallow cannot match the 

 dragon-fly in flight ; this insect has been seen to outstrip and elude 

 its swift pursuer of the feathered class ; nay, it can do more in the 

 air than any bird, it can fly backwards and sidelong, to right or left, 

 as well as forwards, and alter its course on the instant without turn- 



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