The families and genera of insects are so immensely numerous, probably exceeding fifty-fold those of all other land animals, that for this cause alone it would be impossible to enter fully into their distribution. It is also quite unnecessary, because many of the groups are so liable to be transported by accidental causes, that they afford no useful information for our subject; while others are so obscure and uninteresting that they have been very partially collected and studied, and are for this reason equally ineligible. I have therefore selected a few of the largest and most conspicuous families, which have been so assiduously collected in every part of the globe, and so carefully studied at home, as to afford valuable materials for comparison with the vertebrate groups, when we have made due allowance for the dependence of many insects on peculiar forms of vegetation, and the facility with which many of them are transported either in the egg, larva, or perfect state, by winds, currents, and other less known means. I confine myself then, almost exclusively, to the sixteen families of Diurnal Lepidoptera or butterflies, and to six of the most extensive, conspicuous, and popular families of Coleoptera. {103}The number of species of Butterflies is about the same as that of Birds, while the six families of Coleoptera selected, comprise more than twenty thousand species, far exceeding the number of all other vertebrates. These families have all been recently catalogued, so that we have very complete information as to their arrangement and distribution. LEPIDOPTERA DIURNA, OR BUTTERFLIES. Fam. 1. Danaidæ. 2. Satyridæ. 3. Elymniidæ. 4. Morphidæ. 5. Brassolidæ. 6. Acræidæ. 7. Heliconidæ. 8. Nymphalidæ. 9. Libythæidæ. 10. Nemeobiidæ. 11. Eurygonidæ. 12. Erycinidæ. 13. Lycænidæ. 14. Pieridæ. 15. Papilionidæ. 16. Hesperidæ. COLEOPTERA, OR BEETLES. Fam. 1. Cicindelidæ Tiger-beetles. 2. Carabidæ Ground-beetles. 3. Lucanidæ Stag-beetles. 4. Cetoniidæ Rose-chafers. 5. Buprestidæ Metallic Beetles. 6. Longicornia Long-horned Beetles. The above families comprise the extensive series of ground beetles (Carabidæ) containing about 9,000 species, and the Longicorns, which are nearly as numerous and surpass them in variety of form and colour as well as in beauty. The Cetoniidæ and Buprestidæ are among the largest and most brilliant of beetles; the Lucanidæ are pre-eminent for remarkable form, and the Cicindelidæ for elegance; and all the families are especial favourites with entomologists, so that the whole earth has been ransacked to procure fresh species. Results deduced from a study of these will, therefore, fairly represent the phenomena of distribution of Coleoptera, and, as they are very varied in their habits, perhaps of insects in general. {104}MOLLUSCA. The Mollusca are usually divided into five classes as follows:--