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union Is at firft made by a fine thread, and the portions 
are diftinguifhed by a narrow neck, which gradually fills 
up and difappears, the food paffing from one portion to 
another. Portions not only of the fame, but pieces of 
different polypes, may be thus united together. You may 
fix the head of one polype to the trunk of another; and 
that which is thus produced, will grow’, eat, and multi¬ 
ply, like another. There is flill another method of unit¬ 
ing thefe animals together, more wonderful in its nature, 
and lets analogous to any known principles of animation, 
and more difficult to perform. It is effefted by introducing 
one. wdthin the other, forcing the body of one into the 
mouth of the other, and pufhing it dowm fo that their 
heads may be brought together ; in this ftate it mull be 
kept for fome time; the two individuals are at laft united, 
and grafted into each other; and the polype, which was 
at firil double, is converted into one, with a great num¬ 
ber of arms, and performs all its funftions like another. 
Some fpecies furniih us with another prodigy, to which 
we know nothing that is limilar either in the animal or 
vegetable kingdom. They may be turned infide out like 
a glove, and, notwithftanding the apparent improbability 
of the circumftance, they live and aft as before. The 
lining or coating of the llomach now forms the epider¬ 
mis, and the former epidermis now conftitutes the coat¬ 
ing of the llomach. A polype thus turned, may often 
have young ones attached to its fide. If this be the cafe, 
after the operation they are of courfe inclofed in the llo¬ 
mach. Thofe which have acquired a certain fize extend 
themfelves towards the mouth, that they may get out 
when feparated from the body; thofe which are but little 
grown, turn themfelves infide out, and by thefe means 
place themfelves again on the outfide of the parent po¬ 
lype. The polype thus turned combines itlelf a thoufand 
different ways. The fore-part often doles itfelf, and be¬ 
comes a fupernumerary tail. The polype which was at 
firil llraight, now bends itlelf, fo that the two tails re¬ 
ferable the legs of a pair of compafles, which it can open 
and Ihut. The old mouth is at the joint as it were of 
the compalfes ; it cannot, however, aft as one, fo that a 
new' one is formed near it, and in a little time a new lpe- 
cies of hydra is formed with feveral mouths. 
Having given the general hilloryof this curious animal 
fo much at length, we lhall have little more to do than 
to enumerate the different fpecies ; thefe are five in num¬ 
ber, four of which are delineated on the annexed Hydra 
Plate II. 
1. Hydra gelatinofa, the gelatinous polype: minute, 
gelatinous, milk-white, cylindrical, with twelve tentacula 
lliorter than the body. Inhabits Denmark, in clullers on 
the under fide of fuci. See this fpecies on the Plate at 
fig. i, and the fame magnified and difplayed at a. 
2. Hydra viridis, the green hydra : with about ten ten¬ 
tacula fhorter than the body. " Inhabits flagnant waters 
and flow flreams of Europe, generally on the under fur- 
face of plants, and appears like a little tranfparent green 
jelly when contrafted and quiefcent; when expanded it 
is a linear body, fixed at one end, and furrounded at the 
other by tentacula or arms placed in a circle round the 
mouth, and gradually producing its young from the fides, 
which at firil feem fmall papillae, increafing in length, 
fill they affume the form of the parent, and then drop¬ 
ping oil. See fig. 2, and underneath at 6 , a young one, 
lately fallen from the parent, with its tentacula retrafted. 
3. Hydra fufca, the brown hydra: fometimes with 
nine tentacula, as fhown at fig, 3 ; but moflly with eight, 
many times longer than the body. Inhabits frefh waters 
of Europe; grey-brown, a little taper towards the bafe, 
A fpecimen with eight arms is fhown, greatly magnified, 
at fig. 4. 
4. Hydra grifea; the grey polype: with about feven 
tentacula longer than the body. Inhabits rivulets and 
flagnant waters ; yellowifli, tapering tow’ards the bafe ; 
with fometimes twelve arms or tentacula, as at fig. 5. 
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5. Hydra pallens, the pale hydra : with about fix ten¬ 
tacula as long as the body. Inhabits clear w'aters of 
Europe, but not fo common as the others; body pale yel- 
lowifh, tapering towards the bafe, very tender, with whitifh 
tentacula or arms. It brings forth young from all parts 
of its body. 
HY'DRA, a fmall ifl^nd in the Grecian Archipelago. 
Lat. 37 15. N. Ion. 42. 25. E. Ferro. 
HY'DRA-HEADED, adj. Increafing in means of 
flrength : 
Nor ever hydra-headed wilfulnefs 
So foon did lofe his feat. Shakefpeare. 
HYDRAG‘ONUM,yi See Andromeda calyculata. 
HYDRAN'GEA, f [fo named by Gronovius, from 
Gr. water, and ayfo;, a veflel.] In botany a genus of 
the clafs decandria, order digynia, natural order of fuccu- 
lentse, (faxifragas, JuJf.) The generic characters are—Ca¬ 
lyx perianthium one-leafed, five-toothed, permanent, fmall. 
Corolla: petals five, equal, roundifh, larger than the ca¬ 
lyx. Stamina: filaments ten, longer than the corolla ; al¬ 
ternately longer and fhorter. Antherse roundifh, twin. 
Piflillum : germ roundifh, inferior ; flyles two, fhort, dis¬ 
tant; fligmas blunt, permanent. Pericarpium : capfuls 
roundifh, twin, two-beaked with the double ftyle, angu¬ 
lar ’with feveral nerves, crowned with the calyx, two- 
celled with a tranfverfe partition, opening by a hole be¬ 
tween the horns. Seeds : numerous, angular, acuminate, 
very fmall.— EJfential C/iarader. Caplule two-celled, t,wo- 
beaked, containing many feeds ; corolla five-petalled ; ca¬ 
lyx five-cleft, fuperior. 
Species. 1. Hydrangea arborefcens, or fhrubby hydran¬ 
gea : leaves ovate, fmooth, alternate; llamens longep. 
This has a fpreading woody root, which produces feveral 
foft, pithy, woody, flems, from three to four feet high ; 
they are four-cornered when young, and have a green 
bark, but as they grow older they become taper, and have 
a light-brown bark. Leaves at each joint oppofite, three 
inches long, and two broad near the bafe, pointed, ferrate; 
they are deep green above, and pale underneath, with 
many tranfverfe veins; the petioles are about an inch 
long. Flowers terminating in a cyme. Corolla fmall, 
white, having an agreeable odour. The flowers have 
fometimes eight llamens only, according to Du Roi„ 
The calyx is faflened to the pericarp, which is a fmall 
capfule, almofl hemifpherical; marked with ten ftreaks, 
flattifh above, not opening by valves, but by a central 
hole between the flyles. Partition membranaceous, per¬ 
vious at top when ripe. Seeds about twenty in each cell, 
comprefled like a lens, netted-veined, brown. Linnaeus 
had defcribed the capfule as opening between - the 
horns, formed by the two permanent flyles ; we are at 
a lofs to know why in his firil mantilla he correfted this, 
and affirmed that the capfule is what he terms circumfcij'af 
or cut round horizontally into two hemifplieres. Gasrt- 
ner however fuggefls, that, although in all his fpecimens 
the capfules opened by a hole at top, yet in fome it may 
be otherwife, and they may fplit in half horizontally ; of 
this we have an inltance in Heuchera. Native of Virginia 
and Canada. Introduced in 1736, by Peter Collinfon. 
The flowers appear towards the end of July, and in Au- 
guft; but feldom perfeft their feeds in England. 
2. Hydrangea radiata, or downy hydrangea : leaves lobed, 
tomentofeunderneath. This has a fomewhat fhrubby Item, 
branched, and growing to the height of about five feet; 
the leaves are broad, heart-fhaped, ferrated, and fharp- 
pointed ; they are footflalked and Hand oppofite, and the 
lower furface is downy, and of a filvery appearance. Ga¬ 
thered in Carolina by T. Walter, efq. and in Florida by 
Mr. J. Bartram. 
3. Hydrangea hortenfis, garden hydrangea, or Chinefe 
guilder-rofe : leaves elliptical, ferrate, very fmooth ; fta- 
mens all of an equal length. The celebrated Commerfon 
named this fhrub Hortenfia, from Hortenfia Lepaute, the- 
j; wife 
