120 



ENTOMOLOGY. 



in scraping or tearing delicate surfaces. It is by means of 

 this curious structure that the busy house-fly occasions 

 much mischief to the covers of our books, by scraping off 

 the albuminous polish, and leaving tracings of its depreda- 



Fig. 139.— Side view of a labellum. ca, chitinous arch supporting the false 

 tracheae (pt).— After Kraepelin. 



tions in the soiled and spotted appearance which it occasions 

 on them. 



The thorax is somewhat rounded, and though composed 

 of three rings, yet these are so consolidated that it is at first 

 hard to identify them. The prothorax is rudimentary, the 



Fig. 140. — Thorax of the house-fly. prn. pronotum; prsc, praescutum ; sc' meso- 

 scutum; set', mesoscutelliim; pscv, postscutellum; al, insertion of tegula. ex- 

 tending to the insertion of the wings, which have been removed; msphr, meso- 

 phragma; h, balancer (halter); pt, patagia; mtn. metanotum; epis, epis' 

 epis", episternum of pro-, meso- and meta-thorax; epm', epm", meso- ana 

 meta-epimerum; at', at", meso- and meta-sternum; ex', ex'', ex'", coxae; tr', 

 tr", tr'". trochanters of the three pairs of legs; sp', sj)", sp'", sp"", sp'"", 

 first to fifth spiracles; ty', ty", tergites of first and second abdominal seg- 

 ments; W, u", urites. 



thorax being almost wholly formed of the middle ring 

 (meso thorax). The latter consists of three large upper 



