That branch of zoölogy which treats of insects is known as entomology. The _Insecta_ have been variously subdivided by different scientific writers, but the following subdivision has much in it to commend it, and will suffice as an outline for the guidance of the advanced student. CLASS VI. INSECTA (INSECTS PROPER) HETEROMETABOLA For the most part undergoing only a partial metamorphosis in the development from the egg to the imago. ORDERS 1. _Thysanura._ Suborders: _Collembola_ (Podura, Springtails). _Symphyla_ (Scolopendrella). _Cinura_ (Bristletails, etc.). 2. _Dermatoptera_ (Earwigs). 3. _Pseudoneuroptera._ Suborders: _Mallophaga_ (Bird-lice). _Platyptera_ (Stone-flies, Termites, etc.). _Odonata_ (Dragon-flies, etc.). _Ephemerina_ (May-flies, etc.). 4. _Neuroptera_ (Corydalis, Ant-lion, Caddis-flies, etc.). 5. Orthoptera (Cockroach, Mantis, Mole-cricket, Grasshopper, Katydid, etc.). 6. _Hemiptera._ Suborders: _Parasita_ (Lice). _Sternorhyncha_ (Aphids, Mealy Bugs, etc.). _Homoptera_ (Cicada, Tree-hoppers, etc.). _Heteroptera_ (Ranatra, Belostoma, Water-spiders, Squash-bugs, Bedbugs, etc.). 7. _Coleoptera._ Suborders: _Cryptotetramera_ (Lady-birds, etc.). _Cryptopentamera_ (Leaf-beetles, Longhorns, Weevils, etc.). _Heteromera_ (Blister-beetles, Meal-beetles, etc.). _Pentamera_ (Fire-flies, Skipjacks, June-bugs, Dung-beetles, Stag-beetles, Rove-beetles, Tiger-beetles, etc.). METABOLA Undergoing for the most part a complete metamorphosis from egg, through larva and pupa, to imago. ORDERS 8. _Aphaniptera_ (Fleas). 9. _Diptera._ Suborders: _Orthorhapha_ (Hessian Flies, Buffalo-gnats, Mosquitos, Crane-flies, Horse-flies). _Cyclorhapha_ (Syrphus, Bot-flies, Tsetse, House-flies, etc.). 10. _Lepidoptera._ Suborders: _Rhopalocera_ (Butterflies). _Heterocera_ (Moths). 11. _Hymenoptera._ Suborders: _Terebrantia_ (Saw-flies, Gall-wasps, Ichneumon-flies, etc.). _Aculeata_ (Ants, Cuckoo-flies, Digger-wasps, True Wasps, Bees).