ough to cover the larvae or
they perish.

The head of the larvae of most species is wide and flattened. The eyes
are situated at the sides, and just in front of them is a pair of short
antennae which vary with the different species.

The mouth-parts too vary greatly according to the feeding habits. Some
mosquito larvae are predaceous, feeding on the young of other species or
on other insects. These of course have their mouth-parts fitted for
seizing and holding their prey. Most of the wrigglers, however, feed on
algae, diatoms, Protozoa and other minute plant or animal forms which are
swept into the mouth by curious little brush-like organs whose movements
keep a stream of water flowing toward the mouth.

Another group containing the _Anopheles_ are intermediate between these
two and have mouth-parts fitted for feeding on minute organisms as well
as for attacking and holding other larger things.

[Illustration: FIG. 55--Eggs, larvae and pupae of mosquitoes (_T.
incidens_).]

[Illustration: FIG. 56--Larva of mosquito (_T. incidens_).]

[Illustration: FIG. 57--Mosquito larvae and pupae (_T. incidens_) with
their breathing-tubes at the surface of the water.]

[Illustration: FIG. 58--Anopheles larvae (_A. maculipennis_) resting at
the surface of the water.]

A few kinds feed habitually some distance below the surface, others on
the bottom, while still others feed always at the surface. With one or
two exceptions, the larvae must all come to the surface to breathe (Figs.
53-57). Most species have on the eighth abdominal segment a rather long
breathing-tube the tip of which is thrust just above the surface of the
water when they come up for air. In this tube are two large vessels or
tracheae which open just below the tip of the tube and extend forward
through the whole length of the body, giving off branches here and there
that divide into still smaller branches until every part of the body is
reached by some of the small divisions of this tracheal system that
carries the oxygen to all the tissues. The length of the breathing-tube
is correlated with the feeding-habits of the larvae. _Anopheles_ larvae
which feed at the surface have very short tubes (Fig. 58), others that
feed just below the surface have breathing-tubes as long or very much
longer than the ninth abdominal segment. The last segment has at its tip
four thin flat plates, the tracheal gills. These too are larger or
smaller according to the habits of the l