The following list gives the orders or principal groups into which the Class Insecta may be divided. I will not, indeed, here enter upon my own views, but will adopt the system given by Mr. Westwood in his excellent “Introduction to the Modern Classification of Insects,” from which also, as a standard authority, most of the figures on Plates I. to IV., when not otherwise acknowledged, have been taken. He divides insects into thirteen groups, and with reference to eight of them it may be said that there is little difference of opinion among entomologists. These orders are by far the most numerous, and I have placed them in capital letters. As regards the other five there is still much difference of opinion. It must also be observed that Prof. Westwood omits the parasitic Anoplura, as well as the Thysanura and Collembola. ORDERS OF INSECTS ACCORDING TO WESTWOOD. 1. HYMENOPTERA Bees, Wasps, Ants, &c. 2. STREPSIPTERA _Stylops_, _Zenos_, &c. 3. COLEOPTERA Beetles. 4. EUPLEXOPTERA Earwigs. 5. ORTHOPTERA Grasshoppers, Crickets, Cockroaches, &c. 6. THYSANOPTERA _Thrips_. 7. NEUROPTERA _Ephemeras_, &c. 8. TRICHOPTERA _Phryganea_. 9. DIPTERA Flies and Gnats. 10. APHANIPTERA Fleas. 11. HETEROPTERA Bugs. 12. HOMOPTERA _Aphis_, _Coccus_, &c. 13. LEPIDOPTERA Butterflies and Moths. Of these thirteen orders, the eight which I have placed in capital letters—namely the first, third, fifth, seventh, ninth, eleventh, twelfth, and thirteenth, are much the most important in the number and variety of their species; the other five form comparatively small groups. The Strepsiptera are minute insects, parasitic on Hymenoptera: Rossi, by whom they were discovered, regarded them as Hymenopterous; Lamarck placed them among the Diptera; by others they have been considered to be most closely allied to the Coleoptera, but they are now generally treated as an independent order. The Euplexoptera or Earwigs are only too familiar to most of us. Linnæus classed them among the Coleoptera, from which, however, they differ in their transformations. Fabricius, Olivier, and Latreille regarded them as Orthoptera; but Dr. Leach, on account of the structure of their wings, considered them as forming the type of a distinct order, in which view he has been followed by Westwood, Kirby, and many other entomologists. The Thysanoptera, consisting of the Linnæan genus _Thrips_, are minute insects well known to gardeners, differing from the Coleoptera in the nature of their metamorphoses, in which they resemble the Orthoptera and Hemiptera. The structure of the wings and mouth-parts, however, are considered to exclude them from these two orders. The Trichoptera, or Caddis worms, offer many points of resemblance to the Neuroptera, while in others they approach more nearly to the Lepidoptera. According to Westwood, the genus _Phryganea_ “forms the connecting link between the Neuroptera and Lepidoptera.”