330 



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 se^e^t 

 are well shown in the grasshopper. 

 The dorsal part, the tergum, is 

 composed of four pieces, termed 

 sderites, which are especially 

 marked on the prothoracic seg- 

 ment. They are named the pr<z- 

 scutum, scutum, scutellum, and post- 

 scutellum. The side of a thoracic 

 segment is called the pleurum; it 

 consists of three sclerites, the 



FIG. 250. Different forms of 

 antennae of insects, a, bristle-like 

 antenna of a grasshopper, Locusta; 



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



c, moniliform, of a beetle, Tenebrio; 



teron. The underside of each 



d, dentate, of a beetle, Elater ; 



e, pectinate, of Ctenicera; f, crooked, thoracic Segment is Called 



sternum. 



The abdomen 



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

 of beetle, Silpha: h, knobbed, of 

 beetle, Necrophorus ; i, lamellated, 

 of beetle, Mclolontha; k, with 

 bristle, from fly, Sargus. (From 



the 



Sedgwick's Zoology, 

 meister.) 



______ __ is made up of 



eleven segments. The posterior 



after Bur- end m tne f ema l e j s usua lly modi- 

 fied by egg-laying structures (ovi- 

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

 The abdomen is usually punctured by seven pairs of breathing 

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



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

 most interesting external features of insects. The antenna are 



