comparative Chcstotaxy. 507 



Lower fronto-orhital bristles occupy the lower part of 

 the front, above the antenna, along the orbit. They are 

 differentiated from the ordinary fronto- orbital bristles in 

 not being quite in a line with them — that is, in being 

 inserted either a little nearer to the orbit (Trypctidce) or 

 a little farther {Seatophagidce) ; they also differ from the 

 upper fronto-orbital bristles in being smaller or inserted 

 closer together. They are not of frequent occurrence. 



Vibrissa (Meigen, vol. i., xxix.), a stout bristle on the 

 lower end of the facialia, immediately above the peristo- 

 mium and below the antennal fovege on each side, often 

 accompanied by some smaller bristles. Vibrissse are 

 characteristic of some families ; they are wanting in the 

 Trypetidce and OrtalidcB. 



Facial bristles,* inserted in a series on each side of 

 the middle portion of the face, above the vibrissee, along 

 the facialia ; they are especially conspicuous in the 

 Tachinida. They are rare SLinong the AcalyjJtrata ; the 

 Ephydridce, for instance, have some weak ones on each 

 side of the face. 



In some genera other characteristic bristles occur, 

 less persistent than those enumerated above, that is, 

 appearing sometimes in one species and disappearing in 

 another in the same genus. Such is an occipito-orbital 

 bristle in some Ortalidce, inserted on the posterior orbit 

 of the eye ; one or several geiial bristles on the cheek, 

 near the lower corner of the eye, &c. A row of bristles 

 along the posterior orbit of the eye in the Dolichopodidce 

 have been aptly called by Loew cilia of the p)osterior 

 orbit ; similar bristles exist in the Diptera Calyptrata, in 

 the Asilidce, &c. They are often plumose. 



B. Thoracic Dorsal Bristles. 



I divide the thoracic dorsum into regions, as they are 

 indicated by the existing structural features : the dorsal 

 stripes indicative of the position of the longitudinal 

 thoracic muscles, and the thoracic transverse suture (or 

 rather furrow) separating the anterior from the posterior 

 bundles of the vertical muscles. Thus we obtain the 



* Eondani (Proclr., iii., p. 244) calls the facial bristles setcB 

 orales, a term which is misleadiug, hecause oralis means belonging 

 to the mouth, as well as belonging to the face. (We have the oral 

 organs and oral margin, both referring to the mouth). Eondani's 

 other terms, setce verticales, ocellares, and front ales, are the same 

 as mine. 



