400 MODERN CLASSIFICATION OF INSECTS. 



and leathery, the labrum bifid, and the labial palpi short and filiform 

 {fig. 50.9. These details are from F. auricularia). The thorax is 

 sepai'ated into the three ordinary segments; the dorsum of the pro- 

 thorax (pronotum) forms a flattened plate, nearly as large as the 

 head, truncate in front, rounded behind, and margined. As these 

 insects are good walkers, and the legs of equal size, it is essential that 

 the sternum of each of the three thoracic segments should be nearly 

 equally developed, and such is the case. The insects are also fliers ; 

 but the posterior wings alone assist in aerial motion, the minute 

 tegmina, or fore wings, being apparently incapable of rendering it 

 any assistance. The tergum of the mesothorax is therefore very short 

 (without any prominent scutellum), whilst that of the metathorax is 

 large and nearly square : it is divided into two parts in a curious 

 manner, the interior angles of the lower wings being produced inter- 

 nally in a narrow band, until they meet in the middle of the back, 

 and are directed backwards in a point. The fore wings are very 

 small, scarcely concealing more than a fourth part of the abdomen ; 

 the hind wings are large, and, when expanded {fig. 50. lO.), present a 

 beautiful appearance; each wing constitutes more than the quadrant of 

 a circle ; and, at a short distance along the front margin of the wing, 

 is a broad leathery patch, which is the small part of the wing, which 

 is unprotected by the fore wing, when the insect is at rest {fig. 50. 

 \. x). It is therefore essential that this part should be of a firmer 

 consistence than the remainder of the wing : moreover it serves as a 

 place of attachment {fig. 50. lo. o) for the numerous radiating veins 

 by which the wing is traversed, and which are thickened in the 

 middle (i. e. at the distance of two thirds from the base of the wing, 

 fig. 50. 10. b) ; another transverse vein runs parallel with the posterior 

 margin of the wing between the radiating veins. There is also a 

 series of shorter veins, extending from the middle to the posterior 

 margin of the wings. On examining an earwig vvith the wing ex- 

 tended, it seems astonishing how such a large pair of organs can be 

 folded into so small a space ; but this is effected in a beautifully 

 simple manner. The membrane of the wing itself is very delicate, 

 and the action of the radiating veins, in closing the wing, is exactly 

 that of the bars of a fan. The wing (or rather the apical two third 

 portions of it) is thus longitudinally folded into a very small space, 

 and it is then transversely folded at the part {fig. 50. 10. b) where 

 the radiating nerves are thickened ; and a second transverse fold 



