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144 like, and short hairs on the antennæ of the female; this is an easily recognized indication of sex in most species.

The proboscis consists of a number of piercing elements enclosed in a sheath—the labium, which, at its free end, is tipped with two minute labella. In feeding, the mosquito raises her hind legs and presses the tip of the proboscis against the skin. This causes the labella (Fig. 32, h) to splay out and so serve as a support to the piercing elements namely, the labrum, hypopharynx, mandibles, and maxillæ (Figs. 32, 33)—which are now thrust into the skin. The

Fig. 32.—Mouth parts of female mosquito.

labium does not penetrate; as the stabbing elements sink into the skin it bends backwards about its middle, the labella still pressing against the skin and clasping the stilettes. The secretion of the salivary glands (Figs. 11, 14) passes along the salivary duct and thence down a minute canal which traverses the hypopharynx to its tip, and so into the subcutaneous tissues of the bitten animal. It is supposed that the function of this secretion is, by irritating, to determine a flow of blood to the part bitten, and also to prevent coagulation of the blood. To many people this secretion is a powerful irritant, although