33 



COLLEGE ZOOLOGY 



rax, mesothorax, and metathorax. The mesothorax and meta- 

 thorax bear each a pair of wings in most insects. Certain 

 simple species (Aptera, p. 337, Fig. 259) do not possess wings; 

 others (lice and fleas, pp. 341 and 359, Figs. 266 and 296) have 



no wings, but this is because they 

 are degenerate. The flies (Diptera, 

 p. 356, Fig. 292) have a pair of 

 clubbed threads, called balancers 

 or halters, in place of the meta- 

 thoracic wings. Attached to each 

 thoracic segment is a pair of legs. 

 The parts of a thoracic segment 

 are well shown in the grasshopper. 

 The dorsal part, the tergum, is 

 composed of- four pieces, termed 

 sdcrites, which are especially 

 marked on the prothoracic seg- 

 ment. They are named the prce- 

 scutum, scutum, scutdlum, andpost- 

 scutellum. The side of a thoracic 

 FIG. 250. Different forms of se g m ent is called the pleurum; it 



antennae of insects, a, bristle-like . 



antenna of a grasshopper, Locusla; Consists of three SClentCS, the 



b, filiform, O f a beetle, Carabus ; episternum, epimeron, and parap- 



c, momliform, of a beetle, Tenebrlo; ' r 



d, dentate, of a beetle, Elater ; t&TOn. The Underside of each 



^pectinate, of Ctenicera; j Brooked, thoracic segment is called the 



of honey-bee, Apis ; g, club-shaped, 



of beetle, Silpha: h, knobbed, of sternum. 



beetle, Necrophorus ; i, lamented The abdomen is made up Q f 



of beetle, Melolonlha; k, with 



bristle, from fly, Sargus. . (From eleven segments. The posterior 



end in the female is usually modi- 

 fied by egg-laying structures (ovi- 

 positors), and in the male by a copulatory apparatus (genitalid). 

 The abdomen is usually punctured by seven pairs of breathing 

 pores (spiracles) and the thorax generally by two pairs. 



The antennas, mouth-parts, legs, and wings are among the 

 most interesting external features of insects. The antenna are 



Sedgwick's Zoology, 

 meister.) 



after Bur- 



