LETTERS ON ENTOMOLOGY. 113 
large dragon-flies. If these breathing-holes or 
mouths are stopped by plunging the insect in 
oil, or any other thick substance, suffocation is 
the consequence; indeed they may be truly called 
aerial beings, for air is the only circulating me- 
dium through the veins and branches of their 
wings, consequently their activity depends on 
the state of the atmosphere. 
The gnats are but too exquisitely formed for 
our repose. The trunk, if we may so call the 
complex weapon in its mouth, is highly deserving 
of a particular description, though I do not know 
that the beauty of it can console us for the pain 
it causes. It consists of an open cylindrical 
sheath, containing five pieces, which are like 
pikes and saws. The sheath is not slit all the 
way down, and we shall see the reason. The 
point which pierces the skin is composed of several 
others, and comes out of the round end of the 
sheath ; and as this sting, if we may so call it, 
must entirely enter the flesh to draw blood, the 
sheath, which is necessarily strong and stiff, and 
cannot pierce also, bends away the sting, which, 
except at the point, comes out of the slit part, 
and the sheath makes an angle underneath, and 
is drawn up towards the head. I do not know 
whether you can understand this description, 
