154 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



English and Continental entomologists do not recognize so 

 many different orders. 



The two principal criteria used in the modern classification 

 of insects are the structure of the mouth-parts and the char- 

 acter of the development. Of these, the development condi- 

 tion is held to be the more fundamental, although this may be 

 open to question. However, on a primary basis of develop- 

 ment and mouth-part conditions, combined with character 

 of wings, antennas, and to a less extent, of legs and abdominal 

 appendages, insects are now classified into orders in the 

 following way: 



Metamorphosis very slight; biting mouth-parts; 



wingless APTERA 



Metamorphosis incomplete. 



With biting mouth-parts. 



EPHEMERIDA 



Wings membranous. 



PLECOPTERA 

 ODONATA 



ISOPTERA 

 CORRODENTIA 



Fore wings parchment-like / ORTHOPTERA 



I EUPLEXOPTERA 



Wingless MALLOPHAGA 



With sucking mouth-parts / HEMIPTERA 



I THYSANOPTERA 

 Metamorphosis complete. 



With biting mouth-parts. f NEUROPTERA 



With wings membranous I M *COPTERA 



I TRICHOPTERA 



With fore wings thickened COLEOPTERA 



With sucking mouth-parts LEPIDOPTERA 



With lapping or piercing and sucking mouth- j ^ IPTERA 



parts. SlPHONAPTERA 



' I HYMENOPTERA 



Order Aptera. The Aptera undoubtedly include the most 

 primitive of living insects. This primitiveness is shown not 

 alone by the absence of wings, which is the characteristic which 

 gives the order its name, but is manifest also in the very 

 simple and generalized condition of most of the body parts, 

 internal as well as external. 



All the insects of the order are small, but a group of them 



