THE LEGS: THEIR STRUCTURE AND FUNCTIONS 97 



N 



MESO 



FIG. 103. Side view of meso- and meta- 

 thorax of Nantixpa brunnea, showing the upper 

 and lower divisions of the epiinerum (*. em', 

 n. em'', i. em', i. em"); s. epis, i. epis", the 

 same of the episternum. 



like pad or adhesive lobe called the empodium or pulmllus (Fig. lOa, 

 also variously called arolium, palmula, plantula, onychium, its ap- 

 pendage being called parwiy- 

 cliinni and also pseudonychium). 

 It is cleft or bilobate in many 

 flies, but in Sargus trilobate. 

 All these parts vary greatly in 

 shape and relative size in in- 

 sects of different groups, espe- 

 cially Trichoptera, Lepidoptera, 

 Diptera, and Hymenoptera. In 

 certain flies (e.g. Leptogaster) 

 the empodium is wanting 

 (Kolbe). By some writers the 

 middle lobe is called the em- 

 podium and the two others 

 pulvilli. 



The fore legs are usually 

 directed forward to drag the body along, while the middle and 

 hind legs are directed outward and backward to push the body 

 onwards. While arachnids walk on the tip ends of their feet, 

 myriopods, Thysanura, and all larval insects walk on the ends of 

 the claws, but insects generally, especially the adults, are, so to 

 speak, plantigrade, since they walk on all the 

 tarsal joints. In the aquatic forms the middle 

 and hind tarsi are more or less flattened, oar-like, 

 and edged with setae. In leaping insects, as the 

 locusts and grasshoppers, and certain chrysomelids, 

 the hind femora are greatly swollen owing to the 

 development of the muscles within. The tibia, 

 besides bearing large, lateral, external spines, occa- 

 sionally bears at the end one or more spines or 

 spurs called calcaria. The fore tibia also in ants, 

 etc., bear tactile hairs, and chordotonal organs, ;is 

 well as other isolated sense-organs (Janet), and, in 

 grasshoppers, ears. 



In the Carabidae the legs are provided with combs 

 for cleaning the antennae (Fig. 107), and in the bees and ants these 

 cleansing organs are more specialized, the pectinated spine (calcar) 

 being opposed by a tarsal comb (Fig. 106, d ; for the wax-pincers of 

 bees, see g). In general the insects use their more or less spiny 

 legs for cleansing the head, antennae, palpi, wings, etc., and the 



FIG. 104. Divided 

 (ilitrochous) trochanter 

 of an ichneumon : ccc, 

 coxa ; tr, the two divis- 

 ions of the trochan- 

 ter; /', femur. After 

 Sharp. 



