106 DRAGON FLIES VS. MOSQUITOES. 



accessory apparatus by which the perforations of tlie skin 

 are made. 



The second group of mouth parts, the invaginal or 

 sheathing parts, consists of an upper lip (labrum) and an 

 under lip (labium) with its accompanying setae, which latter 

 according to Dimmock form the aggressive cutting or 

 piercing organs of the mosquito. 



The labrum is a thin, lanceolate lamellae of chitin, con- 

 cave along the under side from the basal portion to the tip, 

 and its concavity rests upon and fits to the convexity of 

 the tubular parts of the epiisharynx. It is provided with 

 its own muscles and possesses some independent motion. 

 It serves the purpose, together with the labium, of framing 

 the tensile and extended group of parts just described. 



The labium is a long, tapering clumnel, annulated, and 

 covered with fine hair and scales. At its extremity it 

 carries two lobate appendages — the label he — which are fur- 

 nished with muscles by which these latter can be dilated 

 or contracted. When the combined parts of the surgical 

 group of instruments are entering the skin, they pass be- 

 tween the opened angle of the spread labellae while the 

 labium itself " is seen to be flexing backward in its middle, 

 the labellae holding the clustered file of setae as they pass 

 inward through the tissues of the victim. Reaumur, Mem., 

 plate iv., gives a very good illustration of the bent labium 

 holding in position the other mouth parts in act of 

 stinging. 



Poison Glands. 



This description is found in a letter to Science (Vol. 

 X., page 106, and Vol. XII., page 144) from Professor 

 Macloskie, of Princeton College. 



