Packard has devoted much attention to the subject, and has published two or three successive schemes, of which the following is the most recent:[109] the definitions are those of the author himself, but the information in brackets is given to institute a concordance with the system we adopt:— 1. _Thysanura._ Wingless; often with a spring (equivalent to our _Aptera_). 2. _Dermaptera._ Front wings minute, elytra-like (= _Forficulidae_, a part of our _Orthoptera_). 3. _Orthoptera._ Wings net-veined; fore wings narrow, hind wings folded (= our _Orthoptera_ after subtraction of _Dermaptera_). {174}4. _Platyptera._ Four net-veined wings; mouth parts adapted for biting (= _Termitidae_ and _Mallophaga_, parts of our _Neuroptera_). 5. _Odonata._ Wings net-veined, equal (= _Odonata_, a division of our _Neuroptera_). 6. _Plectoptera._ Wings net-veined, unequal (= _Ephemeridae_, a part of our _Neuroptera_). 7. _Thysanoptera._ Mouth beaklike but with palpi (= our _Thysanoptera_). 8. _Hemiptera._ Mouth parts forming a beak for sucking. No palpi (= our _Hemiptera_). The above eight Orders form the group AMETABOLA, while the following eight constitute the METABOLA:— 9. _Neuroptera._ Wings net-veined; metamorphosis complete (= a small part of our _Neuroptera_). 10. _Mecaptera._ Wings long and narrow (for a small part of our _Neuroptera_; the _Panorpatae_ of Brauer). 11. _Trichoptera._ Wings not net-veined (= our division of _Neuroptera_ with the same name). 12. _Coleoptera._ Fore wings sheathing the hinder ones (= our _Coleoptera_). 13. _Siphonaptera._ Wingless, parasitic. Flea (= a division of _Diptera_). 14. _Diptera._ One pair of wings (= our _Diptera_ after subtraction of _Siphonaptera_). 15. _Lepidoptera._ Four wings (and body) scaled (= our _Lepidoptera_). 16. _Hymenoptera._ Four clear wings; hinder pair small; a tongue (= our _Hymenoptera_).