322 SYSTEMATIC ARRANGEMENT 



are found to correspond in position and function, 

 however different they may be in form, to the parts 

 of the mouth in mandibulated insects, and much 

 ingenuity has been exercised by entomologists in 

 tracing this connexion. All these parts are fully 

 developed in the mouth of Tabanus, arid will be seen 

 by the annexed figure, in which 

 a represents the palpi, b the la- > 

 brum, c the mandibles, d the 

 maxillae, e the tongue, and g 

 the labium. The latter is usu- 

 ally very large and fleshy. Many 

 of the parts just mentioned, how- 

 ever, disappear in certain dipte- 

 rous tribes, and in some (CEstri- 

 dee,} all of them are completely obliterated. 



The antennae are sometimes long and conspicuous, 

 bearing no inconsiderable resemblance, as is remarked 

 by Latreille, both in form and appendages, to those 

 of the nocturnal Lepidoptera. In an extensive sec- 

 tion of the order, again, they are very short, com- 

 posed of only two or three joints, the terminal one 

 of which is commonly spindle-shaped, lenticular, or 

 prismatic, with a simple or plumose bristle springing 

 from its upper side. 



The eyes are lateral, commonly large, those of 

 the males being much the largest, and frequently 

 meeting, or nearly so, on the crown of the head. 

 The facets are sometimes larger on the upper than 

 on the under side of the eye. They are occasionally 

 Variegated with bands of brilliant colours. When 



