io8 NATURAL HISTORY OF AQUATIC INSECTS CH. 



usually quite inconspicuous. Besides these piercing 

 implements, the Gnat is provided with a soft flexible 

 sheath, which represents the labium. This takes the 

 shape of a tube, split along its fore side, which 

 surrounds and protects the delicate parts within. 



Fig. 28. — Head and mouth-parts of female Gnat, a, antenna (first three joints) ; 

 w.r/, ma.\illary palp ; in-, lahrum-epipharyn.x ; /, labium ; »i, mandible ; I'lx, 

 maxilla ; /;, hypopharyn.x. The separated mouth-parts are copied from Dimmock. 



The extremity is divided into two lobes. When the 

 female Gnat makes her attack upon the human skin, 

 she plants the two divisions of the flexible labium 

 upon the spot selected. Then the piercing imple- 

 ments make their puncture, being guided and 

 supported by the labium, in the same way that the 



