CLASSIFICATION OF HEXAPODS.
Seven orders of insects were originally recognized by Linnæus, namely, Neuroptera, Diptera, Hemiptera, Lepidoptera, Coleoptera, Hymenoptera, and Aptera. This classification was based on the organs of flight only, and while in the main resulting in natural divisions which still furnish the basis of more modern classifications, was faulty in several particulars. For instance, the Aptera, which included all wingless insects, was soon found to be a very unnatural assemblage and its components were distributed among the other orders. The establishment of the order Orthoptera by Olivier to include a large and well-defined group of insects associated with the Hemiptera by Linnæus, restored the original seven orders, and this classification has, in the main, been followed by entomologists up to the present time.
Fig. 1.—Pyramid showing the nature of the mouth, and relative rank of the Orders, and the affinities of the Suborders of Insects.
All insects are, in a broad way, referable to one or the other of these seven primary orders by the structure of the wings and the character of the mouth-parts in the imago, and by the nature of their transformations.
Some of these orders are connected by aberrant and osculant families or groups, which have by other authors been variously ranked as independent orders, but which, following Westwood substantially, I have considered, for convenience, as suborders. (See Fifth Report, Insects of Missouri, etc., 1872.)
In the article just cited, I made use of the accompanying diagram in the form of a pyramid ([Fig. 1]), which gives a graphic representation of the distinguishing characters and the relative rank as usually accepted, of the orders and suborders.