I, Dorsal view. II, Ventral view. III, Lateral view. IV, Lateral view with segments separated. _Prothorax_: a, Episternum. b, Sternum. c, Coxa of fore-leg. d, Pronotum. _Mesothorax_: e, Prescutum. f, Scutum. g, Scutellum. h, Post-scutellum. i, Mesophragma. j, _Epimeron_. k, _Episternum_. l, Coxa of middle leg. _Metathorax_: m, Scutum. o, Epimeron. p, Coxa of hind leg. n, _First Abdominal Segment_. t, Tegula at base of fore-wing.] [Illustration: After Miall and Denny, _The Cockroach_, Lovell Reeve & Co. FIG. 4.--Legs and Ventral Thoracic Sclerites of Female Cockroach (_Blatta_). I, Fore-leg and pro-sternum (S) in front of which are the ventral cervical sclerites (c). cx, Coxa. tr, Trochanter. fe, Thigh. tb, Shin. ta, Tarsal segments. II, Middle leg and mesosternum. III, Hind-leg and metasternum. In IIIA, the episternum (a) and epimeron (b) are slightly separated.] _Wings._--Two pairs of wings are present in the vast majority of insects, borne respectively on the mesothorax and metathorax. At the base of the wing, i.e. its attachment to the trunk, we find a highly complex series of small sclerites adapted for the varied movements necessary for flight. Those of the dragon-flies (Odonata) have been described in detail by R. von Lendenfeld (1881). The long axis of the wings, when at rest, lies parallel to the body axis. In this position the outer margin of the wing is the _costa_, the inner the _dorsum_, and the hind-margin the _termen_. The angle between the costa and termen is the _apex_. When the wing is spread, its long axis is more or less at a right angle to the body axis. A wing is an outgrowth from the dorsal and pleural regions of the thoracic segment that bears it, and microscopic examination shows it to consist of a double layer of cuticularized skin, the two layers being in contact except where they are thickened and folded to form the firm tubular nervures, which serve as a supporting framework for the wing membrane, enclose air-tubes, and convey blood. These nervures consist of a series of trunks radiating from the wing-base and usually branching as they approach the wing-margins, the branches being often connected by short transverse nervures, so that the wing-area is marked off into a number of "cells" or areolets. [Illustration: After Quail, _Natural Science_, vol. xiii., J. M. Dent & Co. FIG. 5.--Wing-Neuration in a Cossid Moth. 2, sub-costal; 3, radial; 4, median; 5, cubital; 6, 7, 8, anal nervures.]