453 



THE STUDY OF INSECTS. 



decaying wood, or dry sand ; others live in moss or in water. 

 They have either two pairs of spiracles, one at each end of 



vm+ix 



Fig. 551.— Wing of Leptis. 



the body, or are furnished with tracheal gills. The last 

 segment of the body has a transverse cleft, both above and 



n ; m ' -nfc+j 



vu a +ix 



Fig. 552. — Wing of Xylophagus. 



below, which is furnished above with two processes. The 

 pupae are free. 



The family is of moderate size ; about seventy North 

 American species have been described. 



Family ACROCERID^E (Ac-ro-cer'i-dae). 



The Small-headed Flies. 



These flies are easily recognized by the unusually small 

 head, the large humpbacked thorax, the in- 

 flated abdomen, and the very large alulets 



(Fig- 553). 



The head is composed almost entirely of 

 dontia miseiia. e yes, and in some genera is minute. The 



