Fig. 62—A female mosquito (T. incidens); note the thread-like antennæ.
Fig. 63—A male mosquito (T. incidens); note the feathery antennæ.
THE ADULT
The adult mosquito is altogether too familiar an object to need description, but it is necessary that we keep in mind certain particular points in regard to its structure, in order that we may better understand how it is that it is capable of transmitting disease.
If we examine closely the antennæ of a number of mosquitoes that are bothering us with their too constant attentions we shall see that they all look very much alike ([Fig. 62]), small cylindrical joints bearing whorls of short fine hairs. But if we examine a number of mosquitoes that have been bred from a jar or aquarium we will find two types of antennæ, the one described above belonging to the female. The antennæ of the male ([Fig. 63]) are much more conspicuous on account of the whorl of dense, fine, long hairs on each segment. Another interesting difference in the antennæ is to be noted in the size of the first joint. In both sexes it is short and cup-shaped, but in the male it is somewhat larger. This basal segment contains a highly complex auditory organ which responds to the vibrations of the whorls of hairs on the other segments. Interesting experiments have shown that these hairs vibrate best to the pitch corresponding to middle C on the piano, the same pitch in which the female "sings." Of course mosquitoes and other insects have no voice as we ordinarily understand the word, but produce sound by the rapid vibration of the wings or by the passage of air through the openings of the tracheæ. The males and females are thus easily distinguished and, as we shall see later, this is of some importance for only the females can bite. The males and females differ in another way. Just below the antennæ and at the sides of the proboscis or beak is a pair of three-to five-jointed appendages, the maxillary palpi or mouth-feelers which in the females of most species are very short ([Fig. 64]) while in the males they are usually as long as the proboscis ([Fig. 65]). The females of Anopheles and related forms have palpi quite as long as the males, but they are slender throughout while the male palpi are usually somewhat enlarged toward the tip and bear more or less conspicuous patches of rather long hairs or scales.
