pable of transmitting disease.

If we examine closely the antennae 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
antennae, the one described above belonging to the female. The antennae 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 antennae 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 tracheae. 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
antennae 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.

[Illustration: FIG. 64--Head and thorax of female mosquito
(_Ochlerotatus lativittatus_); the short maxillary palpi are just above
the proboscis and below the thread-like antennae.]

[Illustration: FIG. 65--Head and thorax of male mosquito (_O.
lativittatus_); the maxillary palpi are as long as the proboscis.]

[Illustration: FIG. 66--Head of female mosquito (_Anopheles_), with
mouth-parts separated to show the needle-like parts: _a_, _a_ antennae;
_b_, _b_, palpi; _c_, labrum; _