CHAPTER IX 

 THE INSECTS : HEXAPODA 



Though numberless these insect tribes of air, 

 Though numberless each tribe and species fair, 

 Who wing the moon, and brighten in the blaze, 

 Innumerous as the sands which bend the seas ; 

 These have their organs, arts, and arms, and tools, 

 And functions exercised by various rules. 



H. BROOKE, Universal Beauty. 



Definition of Hexapoda (Gr. hex, six; pom ('pod), foot). 

 The previous chapters have been devoted to entomology, that 

 branch of zoology which treats of insects. The insects belong 

 to the class Hexap'oda, the most numerous of all classes 

 of animals, comprising four fifths of the animal kingdom. 

 Insects are built externally upon the plan of a series of 

 somites, grouped in three regions and with segmented ap- 

 pendages on two of them, the head and thorax. Except 

 in very few cases, where this number is reduced, the imagoes 

 have six legs. Hexapods are found in every variety of situa- 

 tion, though they are, as a whole, adapted to life on the land 

 and in the air. A system of tracheae is universally present 

 in the imagoes, though the young of some species have tra- 

 cheal gills for breathing in the water. 



The hard chitinous covering (exoskeleton) necessitates fre- 

 quent molts to provide for increase in size. The molts may 

 or may not be accompanied by metamorphosis. The most 

 marked change of form is seen in the Coleoptera, Lepidop- 

 tera, Hymenoptera, and Diptera. In the first three of these 

 orders, and in some Diptera, while the change in external 

 form is often considerable, most of the larval organs persist 



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