MOSQUITOES AND FLIES 



the common large black horsefly (Fig. 169 B) will show 

 the nature of the feeding organs with which these flies are 

 equipped. Projecting downward from the lower part of 

 the head are a number of appendages; these are the mouth 

 parts. They correspond in number and in relative posi- 

 tion with the mouth appendages of the grasshopper (Fig. 

 66), but they differ from the latter very much in form 

 because they are adapted to quite a different manner of 

 feeding. The horsefly does not truly bite; it pierces the 

 skin of its victim and sucks up the exuding blood. 



By spreading apart the various pieces that compose the 

 group of mouth parts of the horsefly, it will be seen that 

 there are nine of them in all. Three are median in posi- 

 tion, and therefore single, but the remaining six occur in 

 duplicate on the two sides, forming thus three sets of 

 paired structures. The large club-shaped pieces, how- 

 ever, that lie at the sides of the others, are attached at 

 their bases to the second paired organs and constitute a 

 part of the latter, so that there are really only two sets of 

 paired organs. The anteriormost single piece is the 

 labrum (Fig. 169 B, Lm)\ the first paired organs are the 

 mandibles {Md)\ the second are the maxillae (Mx); the 

 second median piece is the hypopharynx (not seen in 

 Fig. 169 B); and the large, unpaired, hindmost organ is the 

 labium (Lb). The lateral club-shaped pieces are the palpi 

 of the maxillae (MxP/p). 



The labrum is a strong, broad appendage projecting 

 downward from the lower edge of the face (Figs. 169 B, 

 170 A, Lm). Its extremity is tapering, but the tip is 

 blunt; its under surface is traversed by a median groove 

 extending from the tip to the base but closed normally 

 by the hypopharynx (Fig. 170 D, Hphv), which fits against 

 the under side of the labrum and converts the groove into 

 a tube. The upper end of this tube leads directly into the 

 mouth, a small aperture situated between the base of the 

 labrum and the base of the hypopharynx and opening into 

 a large, stiff-walled, bulblike structure (Fig. 170 A, Pmp) 



