ORDER XII. DIPTERA.—GNATS OR MOSQUITOS. 337 
Réaumur tells us that the sting of the Gnat is composed of five parts. 
He acknowledges, however, that it is very difficult to be certain of the exact 
number of these parts, on account of the way in which they are united, and of 
their form. At the present day we know that there are six. Réaumur, as 
also Leuwenhoek, thought he saw two in the form of a sword-blade with 
three edges. These have the points reversed, and are serrated on the convex 
side of the bend. The prick made by so fine a point as that of the sting 
of the Gnat ought not to cause any pain. “The point of the finest needle,” 
says Réaumur, “compared to the sting of the Gnat, is the same as the point 
of the sword compared to that of the needle.” So small a wound would 
heal at once, were it not that it has been imbued with an irritating liquid. 
This liquid may be seen to exude, under different circumstances, from the 
trunk of the Gnat, like a drop of very clear water. 
Réaumur sometimes saw this liquid even in the trunk itself. “There is 
nothing better,” he observes, “to prevent the bad effect of gnat bites than 
at once to dilute the liquid they have left in the wound with water. How- 
ever small this wound may be, it will not be difficult for water to be intro- 
duced. By rubbing, it will at once be enlarged, and there is nothing to do 
but to wash it. I have sometimes found this remedy answer very well.” 
When the insect is about to change from the pupa state, it lies on the sur- 
face of the water, straightening the hind part of its body, and extending 
itself on the surface of the water, above which the thorax is raised. Before 
it has been a moment in this position, its skin splits between the two breath- 
ing trumpets, the split increasing very rapidly in length and breadth. 
“It leaves,” says Réaumur, “a portion of the thorax of the Gnat easily 
to be recognized by the freshness of its color, which is green, and different 
from the skin, in which it was before enveloped, uncovered. 
“As soon as the slit is enlarged, —and to do so sufliciently is but the 
work of a moment, — the fore part of the perfect insect is not long in showing 
itself; and soon afterwards the head appears rising above the edges of the 
opening. But this moment, and those which follow, until the Gnat has 
entirely left its covering, are most critical, and when it is exposed to fearful 
danger. This insect, which lately lived in the water, is suddenly in a _posi- 
tion in which it has nothing to fear so much as water. If it were upset on 
the water, and the water were to touch its thorax or body, it would be fatal. 
This is the way in which it acts in this critical condition: As soon as it has 
got out its head and thorax, it lifts them as high as it is able above the open- 
ing through which they had emerged, and then draws the posterior part of 
its body through the same opening; or rather that part pushes itself for- 
ward by contracting a little and then lengthening again, the roughness of 
the covering from which it desires to extricate itself serving as an assistance. 
