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 Tabanns , and 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 ( (Estri - 
dee ,) all of them are completely obliterated. 
The antenna 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 
