INTRODUCTION. 3 



that, in accordance with the external structure, it forms a striking: 

 contrast with the organization of all the other dipterous families. 



The head of the Dolichopodidae in general is more or less he- 

 mispherical. Its sides are occupied by the large, ovate, hairy 

 eyes (naked only in Medeterus), which usually reach so far down 

 that in most genera there are no cheeks (f/ense) at all, and that 

 on the under side of the head, between the eyes, there is just space 

 enough for the large opening of the mouth, which, in some spe- 

 cies, even encroaches upon a considerable portion of the occipital 

 side of the head. The usually rather broad front bears three 

 ocelli, protected by strong .bristles, and several bristles in both 

 corners of the vertex ; the remainder of its surface has no bristles. 

 The frontal fissure and lunule* are indistinct. The antennae are 

 three-jointed, of very different structure in different genera, nay 

 even often in the sexes of the same species ; the second joint is 

 sometimes rudimentary. The arista is two-jointed, seldom alto- 

 gether bare, generally with a very short pubesceuce, more seldom 

 fringed with longer hairs or even plumose ; its dorsal or apical 

 position affords very constant distinctions between different gene- 

 ra ; its length and the other characters belonging to it differ 

 sometimes even in the two sexes of the same species. The face 

 is usually vertical and smooth ; it has often on its inferior third 

 an elevated transverse swelling, or at least, on each side, near the 

 orbit of the eye, a nodule-like elevation ; seldom does the face 

 reach down to the inferior angle of the eye ; it is always without 

 any bristles, although sometimes it is hairy ; its lower edge is 

 rather sharp, and does not coalesce with the border of the mouth ; 

 from under this edge project the single-jointed palpi, incumbent 

 upon the proboscis (except in Ajihrosylus, where they hang down 

 on its sides) ; they are usually scale-shaped, more seldom lancet- 

 shaped (for instance, in Orthochile) or round, pallet-shaped (in 

 Diostracus) ; in the females they are usually considerably larger 

 than in the males ; sometimes however (in Diostracus), the oppo- 

 site is to be found. 



The proboscis is generally short and (with the exception of 

 Aphrosylus and Orthochile) stout; its opening is wide, more or 

 less surrounded by the protuberant suctorial flaps, which, by clap- 



* For the explanation of these terms, compare Monographs, Vol. I, p. xii. 

 —0. S. 



