IV. INSECTA: HEXAPODA 



405 



tions ot the separate segments. The head (fig. 443) is a continuous capsule 

 in which the following parts are recognized: in front and dorsal clypciis 

 and frons; dorsal and posterior a vertex and an occiput; laterally gencc, 

 ventrally a gula. The appendages show that the head is composed of at 

 least four somites. 



The view that the head consists of six somites is based on the existence of 

 two more seij;ments without appendages in the embryo, a preantennal and a 

 postantennal (premandibular), as well as the fact that the brain consists of three 

 pairs of ganglia (proto-, deuto-, and trito-cerebrum). 



The three thoracic segments bear three pairs of legs, whence the name 

 Hexapoda. The legs (iig. 442) are inserted between pleura and sterna 

 and begin with a short coxa (c), followed l)y a trochanter (tr), also short. 

 The two following joints are long, the first, 

 the femur (fe), being large and containing 

 the muscles; the next, tibia (/), being more 

 slender; the foot, or tarsus {la), is composed 

 of several joints, the last bearing a pair of 

 claws. 



The first of the cephalic appendages, the 

 antennte, are the most leg-like. They spring 

 from the frons alcove the mouth and are 

 innervated from the brain. The number 

 and shape of the anteniial joints xaxy with 

 the group, often with the sex, and according 

 as the single joints are lengthened or short- 

 ened, narrowed or expanded, or provided 

 with appendages, etc., different kinds of 

 antennas — knobbed, club-shaped, toothed, 

 feathered, etc. — are recognized, distinctions of great value in classification. 



The morphology of the three pairs of mouth parts, the mandibles (md), 

 maxillcB (mx), and second ma.xilkc, or labium (la, figs. 443-447), is more 

 interesting. The labium, formed of united right and left appendages, 

 lies beliind the mouth and forms the lower lip, and is in contrast to the 

 upper lip, or labrum {Ir), wliich, however, is not appendicular in char- 

 acter. Both labium and labrum may bear unpaired processes on their 

 oral surfaces, an epipliarynx above, a Jiypopharynx below the mouth, 

 neither of them true appendages. 



The different kinds of food necessitate differences in the character of the 

 mouth parts— chewing, licking, sucking, or piercing— all referable back to the 

 chewing kind, and these in turn are modified legs. In the description of the 

 chewing type it is well to begin with the maxilla: (fig. 444), because of their easy 

 comparison with tlie other mouth parts and with the legs as well. These begin 



Fig. 443. — Head of a grass- 

 hopper, f, clypeus; /, frons; 

 g, gena; I, labium; Ip, labial 

 palpi; Ir, labrum; md, mandi- 

 ble; mp, maxillary palpi; mx, 

 maxilla; 0, occiput; v, vertex. 



