EXTERNAL ANATOMY OF INSECTS. 73 



like piece, projecting but little beyond the clypeus. It is 

 generally pointed ; and its under surface or epipharynx is 

 formed to fit exactly the aperture at the base of the feeler-jaws. 

 It has thus partially the power of a piston, and assists in draw- 

 ing fluids through the tube formed by the united feeler-jaws. 

 In Diptera, the parts of the mouth are generally very obscure ; 

 but when a peculiar mode of feeding requires active exercise, 

 you will find they are called into very obvious existence, and 

 each becomes fully developed. The Diptera, like the hepi- 

 doptera, live principally by suction ; but unlike them, have 

 frequently to pierce the cuticle of the object, the juices of which 

 they seek to extract. This operation calls into action organs 

 which were dormant in the honey-sucking butterflies. The 

 blood-suckers among Diptera offer the best examples of a 

 developed mouth. The upper-lip is large, long and sharp- 

 pointed in Tabanus* In Culex, it is longer still, and more 

 slender. If equal development of the primary parts constitutes 

 perfection in the mouth of insects, then Tabanus and Ctile.v 

 may be said to possess perfect mouths. In these the primary 

 parts are equally developed. In Sphceromias, and other nearly 

 allied genera, you will find the upper-lip deeply grooved be- 

 neath, and partially receiving the other organs, as in Hemip- 

 tera. In Hhyphus, it has a tendency to the same form. In 

 the Asilites, it is plain, stiff, and but half the length of the 

 other organs. In the Empites it is long, and forms the outer 

 cover of the beak of these insects. In Medeterus, if I have not 

 mistaken, it is palmate ; the central lobe being longest, the 

 next to it next in length, and the external ones shortest. In 

 CEstrus, the labrum and whole mouth have disappeared. 

 Clark, in his valuable Essay on the Bots of Horses, speaks of 

 the mouth of (Estrus as a simple aperture f thus implying the 

 existence of a pharynx ; I confess I have not found it. Des- 

 voidy appears to have a new theory regarding the mouths of 

 Diptera. If it prove correct, nearly all the received nomen- 

 clature must fall.' 1 In Hymenoptera the upper-lip is short, 



souvent allongee en pointe, appliqu^e contre la base de la trompe et recue dans la 

 suture moyenne de maniere a fermer exactement le leger ecartement qui se 

 trouve entre ses deux filets. — Savigny. 



b In Plate VI. is represented the mouth of Tabanus bovinus. 



c Os, apertura simplex, neque ullo modo exertum. — Clark. 



d La trompe (proboscis) des Dipteres, selon moi, n'est point formee par la 

 NO. I. VOL. II. L 



