ARTHROPODA 



17 



There are three pairs of legs, each thoracic segment l^earing one pair 

 (Fig. 1). The leg is divided into five articulated parts, — coxa, trochanter, 

 femur, tibia, and tarsus. The attachment to 

 the body is by the short coxa, to which is joined 

 the trochanter which is also short. Following 

 the trochanter are two long segments, — the fe- 

 mur and tibia, the former considerably thicker 

 than the latter and containing the muscles. The 

 tarsus, or foot, follows the tibia, and consists of 

 a number of short segments, the last bearing 

 hook-like structures, or claws. 



Usualty there are two pairs of wmgs arising dorsall,y from the meso- 



FiG. 3. — Diagram of In- 

 sect's Heart: c, constriction 

 between two chambers; v, 

 valves (after Boas, by Kirk- 

 aldy & Pollard). 



Fig. 4. — Mouth-parts of Locust, a biting insect: Labrum, or upper-lip, 

 above, on each side of which are the mandibles, or upper pair of jaws. 

 Labium, or under lip, with labial palpi below. Maxillae, or lower pair of 

 jaws, with maxillary palpi, to right and left (from photomicrograph of 

 mounted specimen, by Hoedt) . 



and metathorax (Fig. 1). They consist, when full.y developed, of two 

 closely apposed chitinous outgrowths, between which are extensions of 



