XII INTRODUCTION. 



character alone, however, the group can not be satisfactorily 

 separated from the anomalous Brachycera, in which the anten- 

 nae are more usually three-jointed, with the third joint divided 

 into segments. Nor can the latter be clearly separated from 

 the true Brachycera, in which the third joint is not annulated. 

 Sometimes the third joint appears to resemble that joint in 

 the true Brachycera, but will be found upon close inspection 

 to be composed of a number of closely united segments or 

 annuli, and it is in these cases that the term complex is applied. 

 This character will be easily understood by examining the 

 third antennal joint of a common horse-fly. Either the com- 

 plex or the simple third joint may terminate in a bristle, 

 usually called an arista, or in a style, that is a more slender 

 portion, which is, however, not bristle-like. It is very evident 

 that both the style and the arista represent only the more or 

 less attenuated distal joints of the flagellum, because in all 

 cases a close examination will show them to be composed of 

 from two to five segments. The arista or style is frequently 

 entirely wanting in the Orthorrhapha, but only rarely is it 

 atrophied among the Cyclorrhapha. The style is always ter- 

 minal, because it is less differentiated from the flagellum, but 

 the arista may be either terminal or dorsal, and it may be 

 inserted close to the base of the third joint. It is also evi- 

 dent here that the change of position is more apparent than 

 real, because it is in reality due to the greater development 

 of the under side of the third joint. In some cases the third 

 joint has developed into most singular structures, as for ex- 

 ample in Neochauna and Klastocera among the Stratiomyid, 

 or Talarocera, Schizotachina, Dichocera and Diglossocera , 

 among the Tachinidse. 



Frequently the arista has short hairs growing from its up- 

 per and lower sides, in whicli cases it is called pubescent ; when 

 the hairs are longer and more feather-like, the arista is said 

 to be plumose ; or, if the hairs are fewer and stronger, pecti- 

 nated. The plumosity or pectination is always stronger on 

 the upper side of the arista. 



