_Legs._--Each segment of the thorax carries a pair of legs. In most insects the leg is built up of nine segments: (1) a broad triangular, sub-globular, conical or cylindrical haunch (_coxa_); (2) a small _trochanter_; (3) an elongate stout thigh (_femur_); (4) a more slender shin (_tibia_); and (5-9) a foot consisting of five _tarsal segments_. The fifth (distal) tarsal segment carries a median adhesive pad--the _pulvillus_--on either side of which is a claw. The pulvillus is probably to be regarded as a true terminal (tenth) segment of the leg, while the claws are highly modified bristles. Numerous bristles are usually present on the thighs, shins and feet of insects, some of them so delicate as to be termed "hairs," others so stout and hard that they are named "spines" or "spurs." In the relative development and shape of the various segments of the leg there is almost endless variety, dependent on the order to which the insect belongs, and the special function--walking, running, climbing, digging or swimming--for which the limb is adapted. The walking of insects has been carefully studied by V. Graber (1877) and J. Demoor (1890), who find that the legs are usually moved in two sets of three, the first and third legs of one side moving with the second leg of the other. One tripod thus affords a firm base of support while the legs of the other tripod are brought forward to their new positions.
[Illustration: After Marlat, _Ent. Bull._ 3, n.s. (U.S. Dept. Agr.).
FIG. 3.--Thorax of Saw-Fly (_Pachynematus_).
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
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.]