KEY TO THE OKDEES 



283 



CHAPTER VI. 



KEY TO THE ORDERS AND THE PRINCIPAL FAMILIES 



OF INSECTS 



Definition Hexapoda. - Insects belong ,to the class 

 Insacta or Hexapoda. They are small animals with 

 bodies divided into three parts, head, thorax, and 

 abdomen. These are placed in longitudinal succession. 

 They breathe, take air, by means of trachea ramifying 

 throughout the body. The main trunks of the trachea 



O / 



open externally at orifices (spiracles) situated at the 

 sides of the body. As appendages they have one pair 

 of antenna?, situated on the head, six legs attached to 

 the thorax, the middle division of the body, four wings 

 in some cases, in others two, always placed on t he- 

 thorax. In some instances insects have no wings. The 

 insect body is composed of a succession of transverse 

 rings or segments, marked in some, obscure in others. 

 It is generally conceded that the number of these 

 rings never exceeds thirteen. This ringed or segmented 

 condition is more marked in the earlier stages of in- 

 sect life. The number of articulated legs is six. In 

 the developing stages these may be present or absent. 



ORDERS. 



A. Insects, wingless and without rudimentary wings, showing 

 no evidence of having descended from winged ancestors. Three 

 pairs of legs. Metamorphosis slight. APTERA. 



AA. Insects, winged, or having rudiments of wings, showing 

 evidence of having descended from winged ancestors. Meta- 

 morphosis varied. 



