?( 24 )
(2) The veins of the wings are covered with scales (which can be
plainly seen with a small magnifying glass). The veins of the
wings of other flies have no scales.
The metamor-
phosis of
mosquitoes.
The following are the stages through which mosquitoes pass before they
reach the adult state. An adult female mosquito lays its eggs on a pool or
other collection of water. In a few hours these eggs hatch into small worm-
like wriggling animals called larvœ, whose life is spent entirely in water.
After a variable time, depending chiefly on the temperature, the larvæ
change their shape and character, and become small comma-shaped creatures
called pupæ which spend their time struggling to the bottom of the
water and floating up to the surface again to breathe. After one or
two days the pupæ are transformed into the adult insect or imago, which
emerges at the surface of the water from the skin or pupa-case en-
closing it, and which it leaves behind in the water. After resting for
a while on the surface of the water, the adult mosquito flies away to
seek its food. The study of mosquitoes therefore includes the study of their
ova, larvœ, pupœ and imagines.
Classification.
Species,
genera, and
sub-families.
For purposes of classification and identification the family of insects
called Culicidœ or mosquitoes has been separated by entomologists into
groups of species, genera and sub-families. Thus, if a large collection of
mosquitoes were in the hands of an entomologist for examination, he would
note in the first place that some of the individuals were of exactly the
same appearance and could not be distinguished from one another; for this
reason he would say that all such individuals were of the same species or
kind. Next he would examine specimens of different species and would
find that although the individuals of one species could be distinguished from
those of another (because, let us say, the legs or wings presented different
colour markings) yet the mosquitoes of perhaps two or three species
possessed an important anatomical character in common, while the mosquitoes
of two or three other species did not possess this character. He could,
therefore, classify the different species in a number of groups or genera, each
genus containing the different species which possessed an important
anatomical character in common. Finally, by examining mosquitoes in
different genera, he might find that the members of one genus were quite
different in an obvious and important anatomical manner from the members