Page:EB1911 - Volume 20.djvu/374

 Olivier subsequently used for the assemblage the name Orthoptera, which is now much better known than the earlier terms. W. Kirby (1815) founded an order Dermaptera for the earwigs, which had formed part of de Geer’s Dermaptera, accepting Olivier’s term Orthoptera for the rest of the assemblage, and as modern research has shown that the earwigs undoubtedly deserve original separation from the cockroaches, grasshoppers, crickets, &c., this terminology will probably become established. W. E. Erichson and other writers added to the Orthoptera a number of families which Linné had included in his order Neuroptera. These families are described and their affinities discussed in the articles and  (qq.v.). In the present article a short account of the characters of the Dermaptera and Orthoptera is given, while for details the reader is referred to special articles on the more interesting families or groups.

The Dermaptera and the Orthoptera agree in having well-developed mandibles, so that the jaws are adapted for biting; in the incomplete fusion of the second maxillae (which form the labium) so that the parts of a typical maxilla can be easily made out (see the description and figures of the cockroach’s jaws under ); in the presence of a large number of excretory (Malpighian) tubes; in the firm texture of the forewings; in the presence of appendages (cerci) on the tenth abdominal segment; and in the absence of a metamorphosis, the young insect after hatching closely resembling the parent.

In addition to the characters just enumerated, the Dermaptera are distinguished by the presence of small but distinct maxillulae (fig. 2, see, ) in association with the tongue (hypopharynx); by the forewings when present being modified into short quadrangular elytra without nervuration, the complex hindwings (fig. 1) being folded beneath these both longitudinally and transversely so that nearly the whole abdomen is left uncovered; and by the entirely mesodermal nature of the genital ducts, which, according to the observations of F. Meinert, open to the exterior by a median aperture, the terminal part of the duct being single, either by the fusion of the primitive paired ducts or by the suppression of one of them. In the vast majority of winged insects the terminal part of the genital system (vagina and ductus ejaculatorius) is unpaired and ectodermal. Thus the condition in the Dermaptera is more primitive than in any other Pterygote order except the Ephemeroptera (Mayflies) which are still more generalized, the primitive mesodermal ducts (oviducts and vasa deferentia) opening by paired apertures as in the Crustacea. In the vast majority of the Dermaptera the cerci are—in the adult insect at least—stout, unjointed appendages forming a strong forceps (fig. 1) which the insect uses in arranging the hindwings beneath the elytra. In at least one genus the unjointed pincers of the forceps are preceded, in the youngest instar by jointed cerci. Very many members of the order are entirely wingless.

There are two families of Dermaptera. The Hemimeridae include the single genus  (q.v.), which contains only two species of curious wingless insects with long, jointed cerci, found among the hair of certain West African rodents. The other family is that of the Forficulidae or s (q.v.), all of which have the cerci modified as a forceps, while wings of the characteristic form described above are present in many of the species.

Order Orthoptera.

The bulk of de Geer’s “Dermaptera” form the order Orthoptera of modern systematists, which includes some 10,000 described species. The insects comprised in it are distinguished from the earwigs by their elongate, rather narrow forewings, which usually cover, or nearly cover, the abdomen when at rest, and which are firmer in texture than the hindwings. The hindwings have a firm costal area, and a more delicate anal area which folds fanwise,

so that they are completely covered by the forewings when the insect rests. Rarely (in certain cockroaches) the hindwing undergoes transverse folding also. Wingless forms are fairly frequent in the order, but their relationship to the allied winged species is evident. The female of the common cockroach (fig. 3a) shows an interesting vestigial condition of the wings, which are but poorly developed in the male (fig. 3b). More important characters of the Orthoptera than the nature of the wings—characters in which they differ from the Dermaptera and agree with the vast majority of winged insects—are the absence of distinct maxillulae and the presence of an unpaired ectodermal tube as the terminal region of the genital system in both sexes. The cerci are nearly always joined, and a typical insectan ovipositor with its three pairs of processes is present in connexion with the vagina of the female. In many Orthoptera this ovipositor is very long and conspicuous (fig. 5). Information as to the internal structure of a typical orthopteron—the cockroach—will be found under.

Classification.—Six families of Orthoptera are here recognized, but most special students of the order consider that these should be rather regarded as super-families, and the number of families greatly multiplied. Those who wish to follow out the classification in detail should refer to some of the recent monographs mentioned below in the bibliography. There is general agreement as to the division of the Orthoptera into three sub-orders or tribes.

I. Phasmodea.—This division includes the single family of the Phasmidae whose members, generally known as “s” (q.v.) and “s” (q.v.), are among the best-known examples of “protective resemblance” to be found in the whole animal kingdom. The prothorax is short and the mesothorax very long, the three pairs of legs closely similar, the wings often highly modified or absent, and the cerci short and unjointed. Each egg is contained in a separate, curiously formed, seed-like capsule, provided with a lid which is raised to allow the escape of the newly-hatched insect.

II. Oothecaria.—In this tribe are included Orthoptera with a large prothorax, whose eggs are enclosed in a common purse or capsule formed by the hardening of a maternal secretion. The Mantidae or “praying insects” have the prothorax elongate and the forelegs powerful and raptorial, while the large, broad head is prominent. The eggs are enclosed in a case attached to a twig or stone and containing many chambers. From this curious habitation the young mantids hang by threads till after their first moult (see ). The Blattidae (fig. 3) or es (q.v.) form the second family of this division. They are readily distinguished by the somewhat rounded prothorax beneath which the head is usually concealed, while the forelegs are unmodified. Sixteen eggs are enclosed together in a compact capsule or “purse” (fig. 4).

III. Saltatoria.—The three families included in this tribe are distinguished by their elongate and powerful hindlegs (fig. 5) which enable them to leap far and high. They are remarkable for the possession of complex ears (described in the article ) and