EOUSE-FLT AND OTHER TWO-WINGED INSECTS. Ill 



a set of springs to open and shut the broad flaps. The in- 

 side of this broad, fleshy expansion is rough, like a rasp, 

 and, as Newport states, "is easily employed by the insect 

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

 this curious structure that the busy house-fly occasions 



Fig. 1^.— Section through the head of the blow-fl^. 6, cranial bladder; f, ful- 

 crum; h, hypophaiynz; «d, salivary duct leading into the throat; o, mayilla. 



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

 the albuminous polish, and leaving tracings of its depreda- 

 tions in the soiled and spotted appearance which it occasions 

 on them." The head of the blow-fly may also be examined 

 with the aid of Figs. 119-122. 



Fig. 121.— Side-view of the lahellum. ca, chltinous arch supporting the false 

 tracheae (j>t). 



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 thorax consisting almost wholly of the middle ring 



