Everything just said in regard to the classification of the higher animals applies likewise to butterflies. Let us take as an illustration the common milkweed butterfly. Linnæus for a fanciful reason gave this insect the name _Plexippus_. This is its specific name, by which it is distinguished from all other butterflies. It belongs to the genus _Anosia_. The genus _Anosia_ is one of the genera which make up the subfamily of the _Euploeinæ_. The _Euploeinæ_ belong to the great family of the _Nymphalidæ_. The _Nymphalidæ_ are a part of the suborder of the _Rhopalocera_, or true butterflies, one of the two great subdivisions of the order _Lepidoptera_, belonging to the great class _Insecta_, the highest class in the subkingdom of the _Arthropoda_. The matter may be represented in a tabular form, in the reverse order from that which has been given:
Subkingdom, _Arthropoda_. Class, _Insecta_. Order, _Lepidoptera_. Suborder, _Rhopalocera_. Family, _Nymphalidæ_. Subfamily, _Euploeinæ_. Genus, _Anosia_. Species, _Plexippus_ (Milkweed Butterfly).
_Varieties._--A still further subdivision is in some cases recognized as necessary. A species which has a wide range over an extensive territory may vary in different parts of the territory within which it is found. The butterflies of certain common European species are found also in Japan and Corea, but, as a rule, they are much larger in the latter countries than they are in Europe, and in some cases more brightly colored. Naturalists have therefore distinguished the Asiatic from the European form by giving the former what is known as a varietal name. Similar differences occur among butterflies on the continent of North America. The great yellow and black-barred swallowtail butterfly known as _Papilio turnus_ occurs from Florida to Alaska. But the specimens from Alaska are always much smaller than those from other regions, and have a very dwarfed appearance. This dwarfed form constitutes what is known as a local race, or variety, of the species. The members of a species which occur upon an island frequently differ in marked respects from specimens which occur upon the adjacent mainland. By insulation and the process of through-breeding the creature has come to acquire characteristics which separate it in a marked degree from the closely allied continental form, and yet not sufficiently to justify us in treating it as a distinct species. It represents what is known as an insular race, or variety, and we give it therefore a varietal name. Naturalists also distinguish between seasonal, dimorphic, melanic, and albino forms. Names descriptive or designatory of these forms are frequently applied to them. All of this will become plainer in the course of the study of the succeeding pages, and in the effort to classify specimens which the student will make.