252 
THE LIVING WORLD, 
The Diptera, or Two-winged Flies, are the most numerous species of 
insects ; their small size, and often their quiet colors, prevent their attracting 
such attention as they deserve, alike as a study for the entomologist and 
because of their relation to man’s interests. Their wings, though tenuous, are 
capable of the most rapid vibration, as in the case of the house-fly, which 
reaches four hundred movements per second. Of the one hundred thousand 
species known, most are the benefactors or useful servants of mankind, destroy¬ 
ing, or at least reducing, matter which would else prove the source of sick¬ 
ness and death; diminishing the number of insects which rob the farmer of 
the rewards of his toil; and illustrating many a lesson which mankind seems 
to require to have repeatedly urged upon his notice. In the colder climates, 
where vegetation is less rank, water less stagnant, and animal life less trouble¬ 
some, the diptera are fewer in species; but as conditions unfavorable to 
animal or human life multiply, these insects likewise increase in number, 
variety and useful activity. Thus do they illustrate the wonderful way in 
which the Creator renders the world fit for the habitancy of his children, and 
increases our sense of responsibility for discharging our duties as persistently 
and as cheerfully as do these little beings. Gnats, mosquitoes, Hessian-flies, 
the wheat-fly, the horse-fly, 
the asilus-fly, and the bott- 
fly are the most interesting 
members of the diptera. 
The Gnat ( culexpipitus) 
has a long and cylindrical 
body; its wings are covered 
with scales; its antennae are 
feather-like; its eyes seem 
to occupy the whole of its 
head, and are protected by 
a net work. The trunk, or 
sucker, is cylindrical, and 
contains a bundle of stings, each of which is composed of six parts; 
its sting is followed up by the injection of an irritating liquid. During 
the larval period it appears as a worm in stagnant waters, and comes to the sur¬ 
face to inhale air for respiration, which it does through organs located in the last 
segment of the body. It sheds its skin several times. As a pupa it has no 
digestive organs, and replaces the posterior air tube of the larva by two ear-like 
appendages on the head. With its last transformation it ceases to be a water- 
insect ; indeed, water is so fatal to it, that if touched by a liquid immediately after 
parting from the pupal stage, it dies at once. During this period, brief as 
measured by the life of man, but doubtless of painful length to the gnat , it 
sails about in its sheath, using its new body as mast and sail. A basin of water, 
a few gnats and a microscope, will enable those who are “ inland bred ” to enjoy 
the spectacle of a miniature sea studded with the sails of many a craft; or to 
dream many a legend of spectral boatmen; or to study those changes’which 
have the. profoundest significance for the biologist. When, finally, the gnat 
liberates itself from its boat-like sheath, it leaves the water forever, and joins the 
insects whose habitation is the dry land. As gnats breed throughout the whole 
year, and at intervals of three or four weeks, it can readily be seen that great 
a. b. c. d. e. the bott, or gad-fey and larva (Gastus equi) 
II. WHEAT BUG (Anisoplia segetum). 
