THE MOUTH-PARTS
The mouth-parts of the mosquito are of course of particular interest to us. At first they appear to consist of a long slender beak or proboscis, but by dissecting and examining with a microscope we find this beak to be made up of several parts ([Fig. 66]). The labium, which is the largest and most conspicuous, is apparently cylindrical but is grooved above throughout its length. At the tip of the labium are the labellæ, two little lobes which serve to guide the piercing organs. Lying in this groove along the upper side of the labium are six very fine, sharp-pointed needles. The uppermost of these, the labrum-epipharynx, or labrum as we will call it, is the largest and is really a hollow tube very slightly open on its under side. Just below this is the hypopharynx, the lateral margins of which are very thin. Down through the median line of the hypopharynx runs a minute duct ([Fig. 67], sal) which, though exceedingly small, is of very great importance, for through it is poured the saliva which may carry the malaria germs into the wound made when the mosquito bites. The other four needles consist of a pair of mandibles which are lance-shaped at the tip and a heavier pair of maxillæ, the tips of which are serrate on one edge.
HOW THE MOSQUITO BITES
When the female mosquito is feeding on man or any other animal the tip of the labium is placed against the surface and the six needles are thrust into the skin, the labellæ serving as guides. As they are thrust deeper and deeper the labium is bowed back to allow them to enter. As soon as the wound is made the insect pours out through the tube of the hypopharynx some of the secretion from the salivary glands and then begins to suck up the blood through the hollow labrum into the pharynx and on into the stomach.
The mouth-parts of the male differ in some important respects from those of the female. The hypopharynx is united to the labium, the mandibles are wanting and the maxillæ are very much reduced so that the insect is unable to pierce the tough skin of animals. The male feeds on the juices of plants as do the females when they cannot get blood. It is not at all necessary for mosquitoes to have the warm blood of man or other animals. Comparatively few of them ever taste blood. They have been seen feeding on blossoms, ripe fruit, watermelons, plant juices, etc. They are very fond of ripe bananas and are fed on them in the laboratory when we wish to keep mosquitoes for experimental purposes.
THE THORAX
The middle part of the body, called the thorax, is really a strong box with heavy walls for the attachment of the powerful wing and leg muscles. The three pairs of legs are covered with hairs and scales, and their tips are provided with a pair of claws which vary somewhat in the different species. The wings ([Fig. 68]) are long and narrow with a characteristic venation. Along the veins and the margin of the wings are the scales which readily enable one to distinguish mosquitoes from other insects that may look much like them. In some species these scales are long and narrow, almost hair-like, in others they are quite broad and flat ([Fig. 69]). Just back of the wings is a pair of balancers, short thread-like processes knobbed at the end. These probably represent the second pair of wings with which most insects are provided, and seem to serve as balancers or orienting organs when the insect is flying. On the sides of the thorax are two small slit-like openings, the breathing-pores. These are the openings into the tracheal or respiratory system.
THE ABDOMEN
The long cylindrical abdomen is composed of eight segments. These are rather strongly chitinized above and below, but a narrow strip along the side is unchitinized. In this strip are situated the abdominal breathing-pores. The tip of the abdomen is furnished with a pair of movable organs, which in the male are variously modified and serve as clasping organs at mating time.