LEGS WIXGS. 



527 



the point with movable spines. Finally the last joint, or tarsus, is 

 less movably articulated. It is simple only in rare cases ; generally 

 it is composed of a number of joints (usually five), of which the 

 last is terminated by movable claws, and sometimes also by lobed 

 appendages. 



Of course the special form of the legs varies according to the mode 

 of locomotion and the special needs of each insect. Legs adapted 

 for running, walking, burrowing, leaping, prehension can be dis- 

 tinguished (fig. 435). The anterior pair only is used for predatory 

 purposes, and in such a leg the tibia and tarsus are bent backward 

 against the femur in the same way that the blade of a pocket-knife 

 folds back against its handle (Mantis, Nepa). The legs used in 

 springing are the posterior pair (Acridium), and they are charac- 

 terised by the powerful femur. Those used in digging are usually 

 the anterior pair, and they may be recognised by the broad, shovel- 

 like tibia (GryUotalpa}. In the swimming legs all the parts are flat, 

 and closely beset with long swimming hairs (Naucoris). The legs 

 used in walking may be 

 distinguished from the 

 ordinary running legs 

 by the broad hairy lower 

 surface of the tarsus 

 (Lamia). 



Wings are only 

 found in the fully de- 

 veloped, sexually adult 

 animals, which are re- 

 latively rarely without 

 them. They are attached 

 to the dorsal surface of the meso- and meta-thorax, being articulated 

 between the notum and pleura. The anterior wings are attached to 

 the meso-thorax, and the posterior wings to the meta-thorax. As 

 regards their form and structure they are thin, superficially expanded 

 plates, consisting of two membranes firmly adhering to one another 

 and continuously connected at the edges. They are usually delicate 

 and transparent, and are traversed by various strongly chitinised 

 bands, the nervures or veins or ribs (fig. 436). 



These nervures, which have a very definite and systematically 

 important course, consist of canals, placed between the two layers of 

 the wing, surrounded by chitin and containing Uood, nerves and 

 especially trachece, the distribution of which corresponds with the 



FIG. 436. Wing of Tipula (after Fr. Brauer). H, Sub- 

 costa; 1, first longitudinal nervure (costa mecliana) ; 

 2, radial rib (radius or sector) ; 3, cubital rib ; 4, dis- 

 coidal rib (or cubitus anticus); 5, submedian (or cubitus 

 posticus) ; 6, anal rib (or postcosta) ; 7, axillar rib ; E, 

 marginal cell ; U, submarginal cell. D, discoidal cell ; 

 I V, posterior marginal cells ; VB, anterior basal 

 cell ; HB, posterior basal cell ; AZ t anal cell. 



