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BACOT : MOSQUITOES AND THE DANGER OF MALARIA.
Publishers of the Journal of Hygiene for their kindness in
allowing me to quote from these articles and to reproduce
charts and illustrations. I must also express my gratitude to
the Trustees of the British Museum (Natural History) for the use
of the block showing the contrast in resting-position of females
of Culex and Anopheles, and to my friend Mr. Hugh Main, for
permission to reproduce his photographs of Theobaldia annulata.
II.—LIFE HISTORY OF MOSQUITOES.
Mosquitoes may be defined simply as biting gnats, as dis-
tinguished from the non-biting species, such as the Chironimids,
which also are referred to very generally under this popular
term. Students of the group will note that this definition
restricts the mosquitoes to Edwards' sub-family Culicinae
of the Culicidae, and excludes the non-biting Chaoborinae and
Dixinae, but for this there is, I think, ample warrant, owing to
long-continued popular usage.
Actually, of course, it is the females alone which suck blood,
while by no means all of the species attack man.
The mosquitoes belong to the large group of insects named
Diptera, in recognition of the fact that the flight of the adults
depends upon the development of the anterior pair of wings
alone, the posterior pair being reduced throughout the order
to small knobbed processes, termed "halteres" or "balancers,"
the functions of which are uncertain.
The numerous species of which this large order is composed,
although frequently very diverse both in form and habit, are
readily distinguished from all other insects by the absence of
the posterior pair of wings. The Coleoptera or beetles, like
the Diptera, depend for their motive power, when flying, upon
the action of two wings only ; but, in their case, it is the posterior
pair which are developed for flight, the anterior pair being
modified to form horny cases which protect the functioning
wings when the beetle is on the ground. The presence of these
covering cases, or elytra, as they are called, is sufficient to
show at a glance the order to which any insect possessing them
belongs.
The Diptera, honoured by being considered the most
specialized of all the orders of insects, unfortunately includes a
greater number and variety of species which are directly harmful