4 8 



ENTOMOLOGY 



FIG. 57. 



tinct pieces, or sclerites, as represented diagrammaticaliy in 

 Fig. 56. Thus the tergum of a wing-bearing segment is re- 

 garded as being composed of four sclerites (tergites, Fig. 57), 

 namely and in order, prascutum, scutum, scutellum and post- 

 scutellum. The scutum and scutellum are commonly evident, 



but the two other sclerites are 

 usually small and may be absent. 

 Each pleuron consists chiefly of 

 two sclerites (pleurites, Fig. 58), 

 separated from each other by a 

 more or less oblique suture. 

 The anterior of these two, which 

 joins the sternum, is termed the 

 episternum; the other, the epi- 

 meron. The former is divided 

 into two sclerites in Odonata and 

 both are so divided in Neuroptera. 

 The sternum, though usually 

 a single plate, is in some in- 

 stances divided into halves, as 

 *.**. *p r ' in the cockroach, or even into 



2, mesoprsescutum ; j, mesoscutum; 4, five SCleritCS ( ForficulidcE) 

 mesoscutellum; 5, mesopostscutellum ; 



6, metapraescutum; 7, metascutum; 8, lO thCSC Should DC added the 



metascutellum; 9, metapostscutellum. p atag i a o f Lepidoptera a pair 

 After NEWPORT. 



of erectile appendages of the 



prothorax; and the paraptera, or tegulce, of Lepidoptera and 

 Hymenoptera a pair of small sclerites at the bases of the 

 front wings. 



Each thoracic segment bears a pair of spiracles in the em- 

 bryo and in some adults as well (Campodea, Heteroptera), 

 but in most imagines there are only two pairs of thoracic 

 spiracles, the suppressed pair being usually the prothoracic. 



The sclerites of the thorax owe their origin probably to 

 local strains on the integument, brought about by the muscles 

 of the thorax. Thus the primitively wingless Thysanura and 

 Collembola have no hard thoracic sclerites, though certain 



