The probofcis of the griat conflits o f a great number o f ex-
.tremely delicate pieces, all concurring to onepurpofe; this is
the inftrument with which it {hikes. the flefh, and fucks the blood
o f animal bodies. The only part exhibited to the naked eye is the
fheath, which contains all the other pieces. The {heath is a cy-
lindric tube, which is flit in fuch a manner, that the infeft can
feparate it from the dart, and bend it more or lefs in proportion
as the dart is plunged into the wound; From this tube the
fling is darted, which confifts o f five or fix blades or lancets,
lying one over the other; fome of thefe are (harpened like a two-
edged fword, while others are barbed, and have a vaft number of
cutting teeth. When this bundle o f blades is introduced into "a
vein, the blood rifes up the .blades as fo many capillary tubes.
The moment the gnat lances it’s dart into the flefh, two or three
•drops of a fluid are infinuated by it into the wound. It is this
fluid which is fuppofed to caufe thofe infupportable itchings that
we feel when flung by this little creature.
Plate XVI. Fig. 1, is the probofcis, or that apparatus o f a
tabanus with which it pierces the fkin o f horfes and oxen, and
nourilhes itfelf with their blood. The Angular and compound
ftrufture, together with the admirable form and"exquifite beauty
o f this apparatus, difcovers fuch a view o f the wifdom, power»
and greatnefs of it’s infinite compofer, as mull ftrike with admiration
every contemplative obferver, and lead him to refledt on
the weaknefs, impotence, and nothingnefs of all human mecha-
nifm, when compared with the immenfe Ikill and inimitable
.finifhing difplayed in the fubjeft before us. The whole of this
formidable apparatus is compofed o f fix parts, (exclufive o f the
two guards, or feelers, a a,) all o f which are inclofed in a flefhy
cafe,
cafe, which in the figure is totally removed, as it contained
nothing remarkably different from that of other infefts with two
wings. The guards or feelers, a a, are of a fpungy or flelhy
fubftance, and are grey, covered with fhort hairs; they are united
to the head by a little joint of the fame texture, which in this
view o f the objeft could not be fhewn. Thefe guards are a defence
to the other parts of the apparatus, as they are laid upon
it fide by fide whenever the animal flings, and by that means pre-
ferve it from external injury. The two lancets, b b and B, evidently
open the wound, and are of a delicate and tender ftrufture,
formed like the difiefting knife of the anatomift, with a {harp
point and {lender edge, but gradually increafing to the back.
The two fhaped inftruments, c c and C, appear as i f intended to
enlarge the wound, by irritating the parts round i t ; to accom-
plifti which, they are jagged, or toothed; they may alfo
ferve, from their hard and horny texture, to defend the tube
e E, which is o f a fofter nature, and tubular, to admit the blood,
and convey it to the ftomach ; this delicate part is inclofed in a
cafe, d D, which entirely covers it. Thefe parts are drawn
feparately at B, C, D, E. De Geer obferves, that it is only the
females that fuck the blood o f animals; and Reaumur declares,
that having made one difgorge itfelf, the blood it threw up appeared
to him to be more than the whole body o f the infeft could
have contained.
The exuvia, or caft {kin o f inlefts, being exceedingly tranfi-
parent, are well adapted for obfervation, as they exhibit the outward
appearance o f the little animal; among thefe we may reckon
thofe of fpiders and cimeces, but particularly the forficula, or
earwig, which is an elegant exuvia. The flings o f infefts vary
4' R not