PLATE XXII. FIG. 2.
A Fly's Wing
WE are shewn here the whole of a Fly's Wing,
of which we examined the parti-
cular Composition in the Fourth Figure of the Twentieth Plate, whereto we
therefore so far refer the Reader ; only observing farther on its general Appearance before
the Microscope, that it somewhat resembles a Sea-Fan, with black Ribs or Fibres dispersed
and branched through it ; between which a sine Membrane or Film like a thin Piece of
Muscovy Talc extends.
It grows from the Thorax, a little more towards the Head than the Center of the Bo-
dy's Gravity : But this Excentricity is wonderfully balanced by its expanded Area, and the
Center of its Vibration lying much more towards the Tail than the Root of the
Wing is.
Our Author tells us, (having made many Trials to find out after what manner the
vibrative Motions of a Fly's Wings are performed) that the extreme Limits of the Vibra-
tions were usually about the Length of the Body distant from one another, tho' often
shorter, and sometimes longer : That commonly the foremost Limit was a little above the
Back, and the hinder somewhat below the Belly ; between which two Limits, if one
may guess by the Sound, the Wing seemed to move backwards and forwards with an
equal Velocity : And these Vibrations between the two Limits are so swift, that 'tis very
likely it makes many hundreds, if not thousands, of Vibrations in a Second of Time ; so
that probably the Wing of a Fly is one of the quickest Vibrations in the World.
Who that considers this can forbear admiring the extreme Vivacity of the governing
Faculty or Anima of the Infect, which is able so to actuate and regulate the Animal Spirits,
as to cause each peculiar Organ to move or act not only with so much Quickness, but
at the same time with such exact Regularity.
M is a little Body, like in Appearance to a long hanging Drop of some transparent viscid
Fluid. This is one of the Ballances or Poises which most Kinds of Flies that have
only two Wings are furnished with. It grows out just under the hinder Part of the
Root of the Wing, and may be observed constantly to move before it. The Use of these
Poises is undoubtedly to keep the Body steady and upright in flying ; for if one of them
be cut off, the Infect will fly as if one Side was over-balanced, and ere long tumble to the
Ground ; and if both be taken away, its Flight is aukward and unsteady, manifesting the
Want of some necessary and essential Part.
