10 (INATS OK MOSgUITOES — CHAPTER I 



proportion in size of these parts are of the highest value 

 in the classification and distinction of species. Beneath 

 the anteniiaB there are, in many Dlptera, longitudinal 

 grooves for their reception, the antennal furrows {fovecc 

 antenna les). The antennae lie in these while in the pupa 

 case, and sometimes even after escape. That part of the 

 head which lies on the side beneath the eyes is called the 

 cheek (gena). The compound eyes are sometimes encom- 

 passed in a greater or less portion of their circumference 

 by a ring, somewhat swollen, and separated, more or less 

 distinctly, from the rest of the surface of the head, and 

 named the orbit, the successive parts of which may be 

 called the anterior {orhita anterior, sive facialis) , the inferior 

 {inferior s. genalis), the posterior {posterior s. occipitalis), 

 the superior {siij)erior s. verticalis), and the frontal {frontalis) 

 orbits. An orbit is also often spoken of when there is no 

 distinct ring ; but in this case there is some difference of 

 colour or structure to mark it off. 



The oral parts of Diptera, destined for sucking, are 

 called the sucker or proboscis. They are either inserted 

 at the end of a more or less prolonged, cylindrical portion 

 of the head called the snout {rostrum), or project from a 

 wide aperture, often occupying a great part of the under 

 surface of the head, called the mouth hole {cantus oris). 

 The common, fleshy root of the oral parts is connected by 

 a membrane with the border of the mouth. This mem- 

 brane often has a fold of sometimes quite a horny con- 

 sistence, and is then called the clypeus {clypeus s. pra- 

 labrum). It is either entirely concealed by the anterior 

 border of the mouth, and is then usually movable, or it 

 projects over it as a ridge, and is then usually immovable, 

 as in the CulicidcB, in which it is usually bare, but is 

 covered with crescentic scales in the genus Stegoniyia, and 

 is densely hairy in Trichoprosopon. The largest of the 

 oral parts in most Diptera is the lleshy under lip {labium), 

 consisting of the stem (stipes) and the knob {capituluin 

 labii), formed by the two suctorial flaps {labella), and 

 modified in the Culicidce into the membranous, scaly 

 sheath which encloses the other mouth parts. Besides 



