II I R 
He n villofe germ and llvle. Seed : one, large, of the fame 
.form with the pericarpium. — EJj'ential Character. Petals 
live ; filaments very long, permanent, f'piral; ltyle lateral'; 
berry one-feeded. 
Species, i. Hirtella Americana, or American hirtella : 
leaves ovate-lanceolate, branchless hirfute, racemes up- 
.l'ight fimple, flowers five-ftamen'ed. This is a tree, with 
,a trunk from twenty-five to thirty feet in,height, and a 
ferruginous bark. Branches wand-like, (battered, fpread- 
jng, lubdivided, round, hirfute; leaves on fhort petioles, 
alternate, frnooth, entire, acuminate, from three to fix 
inches long. Flowers alternate, peduncled, fbmewhat 
rough with hairs. Germ founded, villofe ; ftyle lateral ; 
itigma blunt; berry obovate, comprefl'ed, hairy-rough, 
.dry. Native of Cayenne, where it is called by the French 
hois dc gavlette. 
2. HirtelIatriandria,orthree-;ftainenedhirtella: leavesob- 
long, acuminate; racemes compound, loole; flowers three- 
Itamened. This is a branching tree, fometimes twenty 
feet high. Native of the Well Indies, Martinico, Jamaica, 
and Domingo ; flowering in April and May. 
3. Hirtella paniculata, or panicled hirtella : leaves el¬ 
liptic, Alining, with hairy fubcoriaceous racemes ; upright, 
flowers five-ltamened. Native of Cayenne, where it was 
found by Rohr. 
HIR'TIUS (Aulus), an officer under Julius Casfar, who 
wrote a fupplementary part of the Commentaries publilhed 
in his name. The books compofed by Hirtius are the 
eighth of the Gallic war, and thofe of the Alexandrine 
and African wars. His ftyle is good, but his narrative is 
reckoned iefs clear than that of Casfar himfelf. 
HIRUDO, f. [quafi haurudo , from haurio , Lat. to draw 
out.] In helminthology, the Leech ; a genus belonging 
to the order of vermes inteftina; the characters of which 
are : Body oblong, truncate at both ends, unarmed, car¬ 
tilaginous, arid moves by dilating the head and tail, and 
contractingitfelf into an arch. 
The hifcory of thefe animals is rendered interefting from 
their well-known ufe in furgery. They are in fuch re- 
quelt in fome diftrifts of England, that the poor people 
derive a great part of their l’ubfiftence from collecting 
them for lale; and fome plans have been projected of 
making ponds for the purpofe of breeding them. Such 
ponds, if in good fituations, and properly managed, would, 
no.doubt, prove extremely lucrative to the owners. 
The body of all the fpecies of leeches, when extended, 
is long and (lender, but it is capable of very confiderable 
dilatation and contraction. It is compofed of a great 
number of annules, or, to fpeak more correCtly, of circu¬ 
lar mufcles, which are the principal organs of motion. 
The furface of the fkin, in the diflerent fpecies, is more 
or lefs rough with minute tubercles. To the touch, how¬ 
ever, thefe tubercles are fcarcely fenfible, from the cir- 
cumftance of their being always fmeared with a vifcous 
fluid infoluble in water-, which tranfudes from them. By 
means ot this fluid, the progrefs of the animals’, in fwim- 
ming, as well as in pafling through mud, or amongfl the 
carices. reeds, and other aquatic plants, (about the roots 
and leaves ot which they are chiefly,to be found,) is great¬ 
ly facilitated. 
The head of thefe animals, in a ftate of dilatation, is 
coftfiderably lefs pointed than their pofterior extremity. 
They, have tlie power of attaching themfelves to any hard 
fubftance, both by their head and tail; but it is difficult 
to comprehend by what precife means this is effected. All 
we know is, that they form a concavity beneath each of 
thefe extremities; by which, in the manner of a cupping - 
glal's, they adhere fo firmly, that in fome in fiances their 
body has been torn afunuer, in attempting to detach them. 
The (fracture of the fiefhy difcus, which performs the of¬ 
fice of iucker, cannot eafily be afcertained; for, when the 
fkin which covers it is removed, we obferve only fome 
minute fibres interwoven in different directions. In con- 
fequence of the vacuum, formed by the contraction of the 
. Vol. X. No. 653. '< 
H I R 197 
difens, the animals are fixed by the preflure of a column 
of air correiponding to their, diameter. 
They, fwim like eels, by a ferpentine motion. When 
they would change their place without fwimming, they 
begin by fixing their body at one of tlie extremities, by 
means of the fucker that terminates it. 1 he circular 
mufcles of the (kin then feparately aft, by which the body 
is elongated, by diminiftiing its diameter. When the free 
extremity has reached the place to which tlie animal is 
defirous of extending it, it is applied and made faff to 
that fpot by the fucker, and bec.omes the fixed point of a 
new motion. The animal, having now removed the fucker 
firft made ufe of, draws it, by the operation of the longi¬ 
tudinal fibres of the fkin, towards the other fucker, and 
proceeds, in this manner, to fix each extremity alternately, 
Thefe motions are executed with confiderable rapidity. 
The mouth is a triangular opening, having three ftrong 
and (harp teeth, which meet in the centre, and are capa¬ 
ble of piercing not only the human (kin, but even the 
tender parts of that of the horfe or ox. At the bottom 
of the mouth there is a kind of flefny prominence, 111 
which the tube terminates that conveys the blood from 
the triple wound, formed by the teeth, into the ftomae.i 
of the animal. The ftomach confifts of a great number 
of membranous bags, furniihed with final! valves, in which 
blood has fometimes been known to continue for many 
months without being coagulated. As none of the leeches 
have more than one principal orifice in their bodies, it is 
extremely probable, fays Morand, who has publimea a 
Memoir relpefting thele animals, that all thofe particles 
of the blood they fwallow, which do not afiift in nouriui- 
ing their bodies, may pafs off by tranfpiration, and thus 
form the vifcous fluid which exudes through the fkm. 
This fluid may be obferved in blackiih filaments, in wa¬ 
ter in which leeches are kept. 
It appears that leeches refpire through their mouth. 
The greater part are furnifhed with organs of vi-fion, vary¬ 
ing in number, (according to the fpecies,) from two to 
eight. In many of them, however, no eyes are to be ieen, 
even with high magnifying powers. 
If a leech be cut in two, that part which contains the 
head will continue in life, and, after a time, greatei or 
lefs, according to the feafon, will become a new animal, 
differing in no refpecl whatever from others of its fpecies. 
It fhould appear from this fact, and from fome other ob- 
(ervations, that leeches increafe in fize, not only by the 
developement of their parts, but likewife by augmenta¬ 
tion, that is to fay, that old leeches have a greatei numbei 
of mufcular rings than the young ones. 
Some fpecies of leeches are found in almoft all waters; 
but the greater part of them prefer fuch as are muddy, 
and afford growth to numerous aquatic plants. They a_:e 
common throughout the whole of Europe, but lels lo m 
the fouthern than the northern parts. The duration ot 
their life has not been afcertained; but, besides tae gene¬ 
ral caufes of mortality to which they are fubjeft, fuch as 
the drying up, but more particularly the putrefaction 
(during the heats of hummer), of the wafers that tney 
inhabit, they have many enemies, which are in continual 
purfuit of them for food. Thefe are chiefly different (pe- 
cies of fi(h and water-fowl; but there are alio numerous 
larvae of water’-infefts, and even of perfeft infefts, which 
prey upon them. Even the J leeches themfelves deffroy 
one another. Thofe that have been long without food 
fall, without mercy, upon fuch. as are gorged, and fuck 
out of their bodies the juices with which they are reple- 
nilhed. This circunvilapce has been particularly remarked 
by Vauquelin and fome other naturalifts.; 
Thefe animals will not only fuck the blood, of each 
other, and of quadrupeds and fifties, but will fallen upon 
the larvae of infefts, and numerous kind of vermes, <kc. 
that inhabit the fame waters .in y/hich they live. When¬ 
ever they have opportunity, they go, r ge themfelves till 
their ftomach will contain no mole; Q11..the, contrary, 
3 E when 
