18 1NTEODUCTION. 



1 



>phaxynx, and labrum or labrum-epipharynx. The labial 

 palpi are thought to be wholly wanting or represented by the 

 labella.* The labium is always present, more or less fleshy and 

 provided with muscles. It is grooved or channeled on the upper 

 side to receive the other parts, with the exception of the maxillary 

 palpi, which are free. This sheath is often neai'ly complete, the 

 thin margins touching each other above. At its tip are the pair 

 of joints of variable size called the lips or labella. The maxillae 

 and mandibles are sometimes absent, the mandibles most fre- 

 quently ; when present they are always slender and firm. The 

 hypopharvnx is unpaired and slender, grooved on the upperside 

 and sometimes converted into a nearly complete tube. The 

 labrum, also unpaired, is usually elongate and grooved on the 

 underside, forming by apposition with the hypopharynx a com- 

 plete tube. The mandibles are frequently absent ; in fact, I do 

 not know of their occurrence in anv flies with a simple third 

 antennal joint, and they may be absent in the male when present 

 in the female, as in the TABANID^:. They are always piercing- 

 organs, thin, firm, chitinous, and usually slender. The two 

 maxillae, likewise piercing-organs, find their highest development 

 in such predaceous flies as the ASILOXE. Like the mandibles they 

 are chitinous and slender. In some they are more or less flat- 

 tened, and may have curiously shaped projections at the tip ; 

 usually they are bristle-like. They lie with the maxillas within 

 the sheath of the labium, at either side of the labrum and hypo- 

 pharynx. In some cases the labrum is short, and serves only as 

 a cover for the proximal part of the hypopharynx, but usually it 

 is as long as, or longer than, the hvpopharynx, and has a simple 

 groove on the underside. The hypopharynx is always present 

 in flies in which the mouth-parts are functional. It is, more 

 often, a slender firm organ, grooved upon the upperside, which 

 by apposition with the labrum forms a distinct tube. In some, 

 however, it may form an almost complete tube in itself." 



The mouth in the CULICID^E may be described as consisting of 

 eight pieces of approximately equal length, the labium being 

 slightly longer than the others.t The labrum, or upper lip, is 

 uppermost, and closely united to it on the underside is an equally 

 long but very slender piece known as the epipharvnx.J Two 

 slender lancet-like pieces come next : these are the mandibles, 

 and below these, two " delicate needle-like organs, barbed at the 

 summit, the maxillae." There is also a " thin tubular thread," the 

 so-called hypopharynx, this being connected with a poison gland 

 at its base. Below these is the stoutest piece of all, the labium or 

 lower lip, grooved on its upperside to admit of the reception of all 



* This has been recently contested by Wesche. 



t This description is after Theobald (Monog. Culic. i, p. 3). 



| Theobald recommends abolishing this term, as this piece is really part of 

 the labrum, but there are occasions when, exact reference to it being required, 

 a special term is necessary. 



