lsating vessel, the heart.
This consists of a series of chambers each communicating with the one in
front of it by an opening which is guarded by a valve. When one of these
chambers contracts it forces the blood that is in it forward into the
next chamber which, in its turn, sends it on. As the walls relax the
valves at the sides are opened and the blood that is in the body-cavity
rushes in to fill the empty chamber. As these regular rythmical
pulsations recur the blood is forced forward through the heart into the
head where it bathes the organs there. We shall see in another chapter
that the malarial parasite escapes from the walls of the stomach of the
mosquito into the blood in the body-cavity and finally reaches the
salivary glands. As the heart is constantly driving blood to this part
of the body the parasites readily reach the glands from which they
finally escape into the new host.

[Illustration: FIG. 72--Heads of Culicinae mosquitoes; _a_, male; _b_,
female. (After Manson.)]

[Illustration: FIG. 73--Heads of Anophelinae mosquitoes; _c_, male; _d_,
female. (After Manson.)]

[Illustration: FIG. 74--Wing of _Anopheles maculipennis_.]

[Illustration: FIG. 75--Wing of _Theobaldia incidens_.]

[Illustration: FIG. 76--A non-malarial mosquito (_T. incidens_), male,
standing on the wall.]

[Illustration: FIG. 77--Female of same.]

[Illustration: FIG. 78--A malarial mosquito (_A. maculipennis_), male,
standing on the wall.]

[Illustration: FIG. 79--Female of same.]

CLASSIFICATION

For our purpose it will not be necessary to try to give a system of
classification of all the mosquitoes. Those interested in this phase of
the subject will find several books and papers devoted wholly to it. It
is quite important, however, that we know something about a few of the
more familiar groups and kinds, especially those concerned in the
transmission of diseases.

THE ANOPHELES

In pointing out the differences between male and female mosquitoes we
noted that in one group, the genus _Anopheles_, both sexes have long
maxillary palpi (Figs. 72, 73). This is the most important character
separating this genus from the other common forms and as the
_Anopheles_ are the malaria carriers it is important that this
difference be remembered. Most of the members of this group have spotted
wings (Fig. 74), but as some other common kinds also have spotted wings
(Fig. 75) this character will not always be reliable. When an
_Anoph