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322 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, and will be seen by the annexed figure, in which a represents the palpi, b the labrum, c the mandibles, d the maxillæ, e the tongue, and g the labium. The latter is usually very large and fleshy. Many of the parts just mentioned, however, disappear in certain diptereus tribes, and in some (Œstridæ,) all of them are completely obliterated. The antennæ 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 section of the order, again, they are very short, composed 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