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armed, flowers folitary lateral. Stem herbaceous, annual, 
one foot high, upright, almolt fimple. Flowers blue, on 
one-flowered peduncles; corolla not properly wheel- 
fir aped, but wheel-bell-lhaped. Native of Canton in 
China, in moilt places. 
3. Hydrolea Zeylanica, or Ceylon hydrolea: Item un¬ 
armed, flowers lubracemed, leaves lanceolate. Stem her¬ 
baceous, half a foot high, even, upright, branched. It is 
thus described under the name of Steris in the firft Man¬ 
tilla: Appearance that of a fmall capficum; ftern herba¬ 
ceous, very much branched, and even. Leaves alternate, 
petioled, oval-oblong, quite entire, firarpiflr, even ; pe¬ 
duncles oppoflte to the leaves, axillary or terminating, 
fubdivided or one-flowered. Corolla blue, the fame fize 
as that of capficum. Native of the Eaft Indies. 
4. Hydrolea trigyna, or three-ftyled hydrolea: Item 
fpiny, leaves oblong hirfute, flowers three-ftyled axillary. 
Native of the Welt Indies. 
HYDROL'OGYjyi That part of natural hiftory which 
examines and explains the nature and properties of water 
in general, 
HYDROM'ANCER,./! One that praftifes hydromancy. 
Cole. 
HYDROM'ANCY, f. The act or art of divining or 
foretelling future events by means of water. This is one 
of the four general kinds of divination : the other three 
refpefting the other elements, fire, air, and earth, are de¬ 
nominated refpeftively pyromancy, aeromancy, and geo- 
mancy. 
HYDROMAN'TIC, adj. Belonging to liydromancy. 
Cole. 
HY'DROMEL, f. Honey diluted in nearly an equal 
weight of water. When this liquor has not fermented, 
it is called fimple liydromel ; and, when it has undergone 
the fpirituous fermentation, it is called the vinous liydromel, 
or mead. See the article Honey, p. 265 of this volume. 
HYDROM'ETER, f. An inftrument to meafure the 
gravity, denfity, velocity, force, &c. of water and other 
fluids. See Hydrojlatics, under the article Mechanics. 
Profeffor Beckmann fuppofes it to have been the invention 
of Ar chimedes, though the firft mention of it occurs in 
the fifth century ; and it is noticed in the Letters of Sy- 
nefius to Hypatia. It was afterwards forgotten, and is 
not again mentioned till it occurs in a treadle written 
by Tholden in the year 1600. 
HYDROM'PHALUS,/. A tumor in the navel, arifing 
from a colleftion of water. 
HYDROPH'ACE,/. in botany. See Lemna. 
HYDROPH'ILUS, f. the Water-Lover; in ento¬ 
mology, a genus of coleopterous infects; of which the 
generic characters are: Antennas clavate, the club perfo¬ 
liate ; feelers four, filiform ; hind legs formed for fwim- 
ming, being fringed or finned on the inner fide. This 
genus differs from that of Dytifcus only in the ItruCture 
of the antennas, which, inllead of being fetaceous, are 
Ihort, and furnilhed with a clavated and perfoliated tip 
or knob. Beth are inhabitants of ponds and ftagnant 
waters, where they fwim with much velocity, turning 
round with great dexterity. They are extremely vora¬ 
cious, and deltructive to the more tender aquatic infefts, 
worms, and young filli, which they ravenoufly feize with 
their forked jaws, and deftroy by fucking out their juices. 
It may be added, that the hydrophili, like the dytifei, 
iometimes emerge from the waters, and fly about the 
fields, and thus migrate occafionally from water to water; 
but, as this happens chiefly by night, it is not generally 
obferved. The genus hydrophilus, like that of dytifcus, 
has been greatly increafed by the perfevering rel’earches 
of modern entomologifts. Dr. Turton enumerates thirty- 
one fpecies. 
j. Hydrophilus piceus, the water-clock. This is per¬ 
haps the largelt of the Britifli coleoptera, if we except 
the lucanus cervus; meafuring nearly an inch and a half 
in length. It is entirely black, and of a fimooth furface, 
and is particularly diftinguiflied by the form of its thorax, 
3 
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which is produced beneath into a very long and fnarp- 
pointed fpine, ftretching to a confiderable diftance down 
the abdotflen : the hind-legs .are furnilhed on each fide 
with ftrong, but very fine, hairs, as in the dytifei, which 
the animal rel'embles in its manners. It is a native of 
ftagnant waters, where its larva is principally oblerved to 
prey on the fmaller kind of water-fr.ails, and is dirtin- 
guilhed by a particularity in the higheft degree remark¬ 
able : this confifts in the apparently anomalous fituation 
of the legs, which feem, unlefs very accurately confidered, 
to be placed, not beneath the thorax, as in other infects, 
but on the upper part, and from thence to be deflefted 
towards the fides. This uncommon appearance however 
is'not owing to areal dorfal infertion of the legs, but 
principally to the peculiar fhape and pofition of the 
head; and the deception is fo much heightened by the 
inverted pofture in which the infeft generally fwims and 
refts, that it is by no means eafy even for the moft feien- 
tific obferver to diveft himfolf of the erroneous idea be¬ 
fore mentioned. Frifch, in his Hiffory of Infefts, appears 
to have been completely convinced of the reality of the 
dorfal infertion of the legs; and‘the celebrated Reaumur, 
having difeovered fomething fimilar in another aquatic 
infe£t, was fo ftruck with the unufual appearance, that 
he has commemorated it as a circumftance unparalleled 
in the animal world. The author of the fourth volume 
of Seba’s Thefaurus was of the fame opinion; and ex- 
prefsly warns his readers, that his engraver, thinking to 
rectify what he fuppofed an erroneous drawing, has re- 
prefented the legs in this larva as fituated beneath the 
thorax, and not on the upper part. The fagacious Lyonet, 
in his obfervations on Lefier’s Theologie des Infeffes, 
teems to have been the firft who detected the common 
error, and afeertained the real llruflure of the animal, 
which he has clearly and fatisfaflorily explained. The 
larvae are fuppofed to remain about two years before 
they change into pupae or chryfalides. When the larva 
is arrived at its full growth, it fecretes itfelf in the bank 
of the water it inhabits, and, having formed a convenient 
cavity or cell, lies dormant for fome time, after which it 
divefts itfelf of its lkin, and appears in the form of a 
chryfalis, in which ftate having continued for fome time 
longer, it again delivers itfelf from its exuviae, and ap¬ 
pears in its complete or beetle form. When firft difen- 
gaged from the lkin of the chryfalis, it is of a pale colour, 
and very tender; but in the fpace of a few hours the 
elytra or wing-cafes acquire a degree of ftrength and 
colour, which gradually grows more and more intenfe, 
till the animal, finding itfelf fufficiently ftrong, comes 
forth from its retreat, and commits itfelf in its new form 
to the waters. The male is diftinguiflied from the female 
by the ftrufture of the fore-legs, which, as in the genus 
dytifcus, are furnilhed, near the fetting-on of the feet, 
with a fort of horny concave flap or fliield; the legs of 
the females being deftitufe of this part. The ftru&ure 
of the hind legs is finely calculated for the animal’s aqua¬ 
tic mode of life, being furnilhed on the infide with a 
feries of clofe-fet filaments, fo as to give a fort of finny 
appearance to the legs, and to enable the animal to fwim 
with the greateft eafe and celerity. It may be added, 
that the female of the Hydrophilus piceus affords an ex¬ 
ample of a faculty which feems to be exercifed by no 
other coleopterous infeft; viz. that of fpinning a kind of 
web or flattifti circular cafe of filk, which it leaves floating 
on the water, and in which it depofits its eggs. This 
cafe is terminated on its upper furface by a lengthened 
conical procefs refembling a horn, of a brown colour, 
and of a much ftronger or denier nature than the cafe 
itfelf, which is white. The young larvae, as foon as 
hatched, make their efcape from the envelopment of the 
cafe, and commit themfelves to the water. This curious 
particular in the hiftory of the hydrophilus piceus was 
firft difeovered by Lyonet. 
2. Hydrophilus olivaceus: olive; fternum channelled 
with a long recurved fpine ; fnelis emarginate. Body en¬ 
tirely 
