ches from the middle of the thorax to beyond the middle of the
abdomen. At its posterior end are given off five long slender processes,
the Malpighian tubules which are organs of excretion, acting like the
kidneys of higher animals. The hindgut is that portion of the intestine
from the stomach to the end of the body.

[Illustration: FIG. 68--Wing of Mosquito (_O. lativittatus_).]

[Illustration: FIG. 69--End of mosquito wing highly magnified to show
the scales on the veins.]

[Illustration: FIG. 70--Diagram to show the alimentary canal and
salivary glands of a mosquito.]

[Illustration: FIG. 71--Salivary glands of _Culex_ at right. _Anopheles_
at left. (After Christophers.)]

THE SALIVARY GLANDS

Lying under the alimentary canal in the forward part of the thorax are
the salivary glands. There are two sets of these, each having three
lobes with a common duct which joins the duct from the other set a short
distance before they enter the base of the hypopharynx. Each of these
lobes is made up of a layer of secreting cells (Fig. 71) which produces
the saliva that is poured into the wound as soon as the insect pierces
the skin of the victim, and we shall see, too, that the malarial germs
also collect in these glands to be carried by the saliva to the new
host.

EFFECTS OF THE BITE

After a mosquito has bitten a person and withdrawn the stylets, a small
area about the puncture whitens, then soon becomes pink and begins to
swell, then to itch and burn. Some people suffer much more from the
bites of mosquitoes than do others. For some such bites mean little or
no inconvenience, indeed may pass wholly unnoticed, to others a single
bite may mean much annoyance, and several bites may cause much
suffering.

After an hour or so the itching usually ceases, but in some cases it
continues longer. In some instances little or no irritation is felt
until some hours, sometimes as much as a day, after the bite. In such
cases the effect of the bite is apt to be severe and to last for several
days. Sometimes a more or less serious sore will follow a bite, probably
due to infection of the wound by scratching. It is doubtless the saliva
that is poured into the wound that causes the irritation. It is
frequently asserted that if the mosquito is allowed to drink its fill
and withdraw its beak without being disturbed no evil results will
follow. Those who hold this theory say that the saliva that is poured
into the wound is all with