NO. 8 ANATOMICAL LIFE OF THE MOSQUITO SNODGRASS 55 



attracted to dark objects. Experimentally they orient toward black 

 stripes on a white background, and continue to do so when the stripes 

 are rotated about them. When confronted by two black stripes, they 

 face one or the other and not the intervening space. In a wind tunnel 

 freely flying mosquitoes move against the current. 



THE ORGANS OF FEEDING 



The feeding organs of the adult mosquito include the proboscis 

 and two sucking pumps. One of the latter is a preoral cibarial pump 

 beneath the clypeus, the other is a pharyngeal pump, being a part of 

 the alimentary canal behind the brain in the back of the head. In 

 describing the feeding organs of the adult it will be better to take 

 the female first, because in most mosquitoes she is the biting and 

 bloodsucking member of the species and has the mouth parts fully 

 developed. In the nectar-feeding male some of the parts are much 

 reduced or absent. 



The proboscis. — The slender, rodlike proboscis in the female 

 mosquito is usually composed of all the mouth parts possessed by in- 

 sects that feed on solid food, namely, a labrum, a pair of mandibles, a 

 hypo pharynx, a pair of maxillae, and a labium, but the parts are all 

 structurally modified in adaptation to the mosquito's way of feeding. 

 The relation of the parts in the undisturbed proboscis is best seen 

 in a cross section (fig. 20 G). In the deeply channeled upper side of 

 the labium (Lb) are enclosed the labrum (Lm), the mandibles (Md), 

 the hypopharynx (Hphy), and the maxillae (Mx). The labrum itself 

 is practically an inverted tube, since its margins are curved downward 

 and may overlap. The enclosed labral canal (fc) is the food conduit. 

 The hypopharynx contains the salivary canal (sc). By careful 

 manipulation with a dissecting needle all these parts can be separated 

 as shown at E. 



The labrum (fig. 20 H, Lm) is the thickest and the strongest of the 

 stylets. It is movable by muscles from the clypeus attached on its 

 base (fig. 24 D), but the muscles simply elevate and depress the 

 labrum, which is firmly hinged on the clypeus. The term "labrum- 

 epipharynx" often applied to the labrum is quite unnecessary, since in 

 its general form the labrum is a flat lobe of the head and therefore 

 has an upper and lower surface. In the mosquito the decurvature of 

 the lateral parts converts the labrum into a tube through which the 

 ingested liquid food is drawn up by the sucking apparatus at its 

 base. At the sharp-pointed distal end (fig. 20 H, Lm) the walls of the 

 channel diverge to make an opening like that of a hypodermic needle. 



