FIG. 138.—Venation of fore and hind wings of _Micropteryx purpurella_: _j_, jugum, on each wing; _d_, discal vein; the Roman numerals indicate veins I.-VIII. and their branches. ] In the wings of Orthoptera as well as other insects, the fore wings, especially, are divided into three well-marked areas, the costal, median, and internal; of these the median area is the largest, and in grasshoppers and crickets is more or less modified to form the musical apparatus, consisting of the drum-like resonant area, with the file or bow. =The squamæ.=—In the calyptrate Muscidæ, a large scale-like membranous broad orbicular whitish process is situated beneath the base of the wing, above the halter; (Fig. 94, 10 _sq._) it is either small or wanting in the acalyptrate muscids. Kirby and Spence state that when the insect is at rest the two divisions of this double lobe are folded over each other, but are extended during flight. Their exact use is unknown. Kolbe, following other German authors, considers the term _squama_ as applicable to the whole structure, restricting the term _alula_ to the other lobe-like division. More recently (1890 and 1897) Osten-Sacken recommends “_squamæ_; in the plural, as a designation for both of these organs taken together; _squama_, in the singular, would mean the posterior squama alone, and _antisquama_ the anterior squama alone;” the strip of membrane running in some cases between them, or connecting the squama with the scutellum, should be called the _post-alar membrane_. By a mistake Loew, and others following him, used the word _tegula_ for _squama_, but this term should be restricted to the sclerite of the mesothorax previously so designated (Fig. 90, _A_, _t_). The squama or its two subdivisions has also by various authors been termed alula, calypta, squamula, lobulus, axillary lobe, aileron, cuilleron, schuppen, and scale. (Berlin Ent. Zeitschrift, xli, 1896, pp. 285–288, 328, 338.) =The halteres.=—In the Diptera the hind wings are modified to form the _halteres_ or balancers, which are present in all the species, even in Nycteribia, but are absent in Braula. Meinert finds structures in the Lepidoptera which he considers as the homologues of the halteres of Diptera. “In the Noctuidæ,” he remarks, “I find arising from the fourth thoracic segment (segment médiaire), but covered by hair, an organ like the halter of Diptera.” (Ent. Tidskrift., i, 1880, p. 168.) He gives no details. In the Stylopidæ, on the contrary, the fore wings are reduced to little narrow pads, while the hind wings are of great size. The _thyridium_ is a whitish spot marking a break in the cubital vein of the fore wing of Trichoptera; these minute thyridia occur in the fore wings of the saw-flies; there is also an intercostal thyridium on the costal part of the wings of Dermaptera.