2\2 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 Culicince 
of the Culicidce, and excludes the non-biting Chaoborince and 
Dixince, 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 
