An EXPLANATION of the TWENTIETH PLATE
FIG 1.
The Foot of a Fly
THE Foot of a Fly is the Object now before us,
consisting of three Joints, two
Talons, and as many Pattens, Soles, or Spunges, as they are called by some : By
the wonderful Contrivance of which Instruments this Creature is enabled to walk perpen-
dicularly upwards, even against the Sides of Glass ; nay to suspend itself, and walk with
its Body downwards, on the Ceilings of Rooms, and the under Surfaces of most other
Things, with as much seeming Facility and Firmness, as if it were a kind of Antipede,
and had a Tendency upwards : but the quite contrary is evident from its being unable to
suspend itself on the under Surface of a clean and well-polish'd Glass.
The two Talons are handsomely shaped, in the Manner represented A B, and A C,
and are very large in Proportion to the rest of the Foot. The bigger Part of them from
A to d d, is bristled or hairy all over, but from thence towards C and B, the Tops or
Points which turn downwards and inwards, are smooth and very sharp. Each Talon
moves on a Joint at A, whereby the Fly is able to shut or open them at Pleasure:
So that the Points B, and C, having enter'd the Pores of any Thing, and the Fly en-
deavouring to shut its Talons, they not only draw against, and by that means fasten
each other, but also pull forwards all the Parts of the Foot G G, A, D D : and at the
same Time the Tenters or sharp Points G G G G (whereof a Fly has two at every
Joint) run into the Pores, if they find any, or, on a soft Place, make their own Way.
Somewhat of this Kind may be discerned by the naked Eye in the Feet of a Chafer,
and if it be suffered to creep over the Hand or any tender Part of the Body, its Man-
ner of Stepping will be as sensible to the Feeling as to the Sight.
But as the Chafer, notwithstanding this Contrivance to fasten its Claws, often falls when
it attempts to walk on hard and close Bodies, so likewise would the Fly, had not Nature
furnish'd his Foot with a couple of Pattens or Spunges D D, which we are now going
to describe.
From the Bottom or under Part of the last Joynt of the Foot K, two small thin plated
horny Snbstances proceed, each consisting of two flat Pieces D D. These, about F F,
f f, seem to be flexible like the Covers of a Book ; whereby the two Sides e e, e e,
do not always lie in the same Plane, but may sometimes shut closer, so that each of
them can take a little hold. But this is not all, for the Bottoms of these Spunges are
every where beset with small Bristles or Tenters, like the Wire Teeth in a Wool-Card,
with all their Points inclining forwards : by which the two Talons drawing the Foot for-
wards, as before described, and the Spunges being applyed to the Surface of the Body
the Fly walks upon, with the Points of all their Bristles looking forwards and outwards,
as expressed in the Figure if the Surface of the Body has any Irregularity, o?
gives Way in any Manner, the Fly can suspend itself, or walk thereon very easily and
firmly. And its being able to walk on Glass, proceeds partly from some little Rugged-
ness thereon, but chiefly from a Kind of Tarnish or dirty smoky Substance, which ad-
heres to the Surface of that very hard Body ; so that although the tharp Points on the
Spunges cannot penetrate the Surface of Glass, they may easily enough catch hold of the
Tarnish it has contracted.
Some indeed have supposed these Spunges filled with an imaginary Glew, which fixes
the Fly, in such a Manner as to prevent its falling ; but if there was such a sticky
Matter, 'tis not easy to conceive how the Feet could so readily again be loosen'd, and
and move so nimbly forwards. And as our Senses can furnish us with a rational Way of
performing this by the curious Mechanism of the Parts employ'd, 'twould be wrong to
introduce unintelligible Explications.
y y y are some very long, stiff, sharp-pointed Hairs or Bristles.
