The labrum and clypeus are developed as a single prolongation of the oral piece, not as a pair of appendages.
Comstock and C. Kochi believe that the labrum belongs to it,, The appendages of the posterior three or trophal segments become the parts of the mouth.
On the 1 A pair of round tubercles on the labrum (camerostome or hypostoma) of several species of Trilobites has been described and held to be a pair of eyes (22).
The tip of the proboscis is armed with a complicated series of chitinous teeth and rasps, by means of which the fly is enabled to pierce the skin of its victim; as usual in Diptera the organ is closed on the upper side by the labrum, or upper lip, and contains the hypopharynx or common outlet of the paired salivary glands, which are situated in the abdomen.
The Corixidae are small flattened water-bugs, with very short unjointed beak, the labrum being enclosed within the second From Marlatt, Bull.