14 



ECONOMIC ENTOMOLOGY 



■tr 



f 



tb 



(b) Thorax. — The thorax is composed of three segments — the 

 pro-, meso-, and meiaihorax, each having a pair of legs. The meso- 

 thorax and metathorax bear wings. Each segment is divided into a 

 dorsal part, the notum or tergum, a ventral part, the sternum, and 

 two laterals, the pleura (Fig. 17). Each part is again divided by 

 sutures into sclerites — the notum into prcescutum, 

 scutum, scutellum and post-scutellum, and the pleuron 

 into episternum and cpimeron (Fig. 18). 



In most hymenopterous insects the first abdom- 

 inal segment — the propodeum or median segment 

 — is fused with the thoracic mass, so that the petiole 

 of such insects is not the first but the second abdom- 

 inal segment. 



Legs. — Each leg is composed of the following 

 parts: coxa, trochanter, femur, tibia, and tarsus (Fig. 

 19). The trochanter in certain Hyraenoptera is 

 made of two segments, while the tarsus in most in- 

 sects is composed of several segments, the last bear- 

 ing a pair of claws. In some insects, e.g., the Diptera, 

 three appendages are borne between the claws, in 

 which case the outer pair are termed pulvilli and the 

 middle one the empodium. 



Wings. — The two pairs of wings are attached to 

 the meso- and the metathorax. They are membran- 

 ous expansions of the body wall with hollow thick- 

 enings along certain lines called veins or nerves. 

 These veins often branch and interlace, and the spaces 

 between the veins are called cells. Much import- 

 ance is attached in classification to the wing and its 

 veins on account of the great variation not only in 

 the orders and families but even in the genera of a 

 family. 



Structurally the wings of insects may be grouped 



into three divisions: 



I. Where the fore and hind wings are of similar texture and more or 



less fan-like. Under this division fall the Dragon flies, in which both the 



size and form of the wings are very much alike. Butterflies, wasps, and 



bees have their hind wings smaller than the fore wings, while some of the 



Fig. 19. — Leg 

 of a beetle {Calo- 

 ioma caliduni). 

 c, Coxa; c/., claws; 

 /., femur; i., spur; 

 t.^-t.'^, tarsal seg- 

 ments; tb., tibia; 

 tr., trochanter. 

 {After Folsotn.) 



