\ 
II Y D R A. 62M 
out its whole thicknefs will be found to confift of an in¬ 
finite number of thefe grains. To know whether the 
infide of the ftomach was formed of fimilar grains, feveral 
of them have been laid open and examined by the mi- 
crol'cope ; the interior lfirface was then found to conliit 
of an immenfe number of them, being as it were more 
fhagreened than the exterior one, and lefs tranfparent. 
The grains are not ftrongly united to each other, but 
may be feparated without much trouble. If a polype be 
carefully placed before the microfcope, without wound¬ 
ing it, you will feldom be difappointed in feeing fome of 
thefe grains detach themfeves from the fuperficies thereof, 
and that even in the molt healthy. But, if the grains 
feparate themfelves in large quantities, it is the fymptom 
of a very dangerous diforder; the furface of the polype 
thus attacked becomes more and more irregular, and is 
no longer well terminated and defined as before. The 
grains fall off on all Tides, the body and arms contrail and 
dilate, it becomes of a white Ihining colour, lofes its form, 
and at length diffolves into a heap of grains. 
A very attentive and accurate examination fhows that 
the ikin is formed of a kind of glareous l'ubftance, a fpe- 
cies of guin, which tills up the intervals between the 
grains, in which they are lodged, and by which they are 
attached, though weakly, together. It has been already 
obferved,that it is to thefe grains that it owes it fhagreen- 
like appearance ; it is from them alfo that it derives its 
colour; for, when they are feparated from the polype, 
they are of the fune colour with it, whereas the glareous 
matter is without any diftinguifhing colour. The con- 
ftru&ion of the polype feems then to be confined to thefe 
glandular grains, to the vifcous matter, and the invifible 
fibres which act upon the glareous fubftance. 
All animals of this kind have a remarkable attachment 
to turn towards the light, and this plight naturally in¬ 
duce the inquirer to look for their eyes ; but how care¬ 
fully foever this fearch has been purified, and however 
excellent the microfcope with which every part has been 
examined, yet no appearance of this organ has been 
found. Notwithllanding this, they conftantly turn them¬ 
felves tQward the light; fo that, if that part of the glafs 
In which we place them be turned from it, they will be 
found the next day to have removed themfelves to the 
fide that is next the light, and the dark fide will be quite 
depopulated. 
The polypes are in general very voracious; an hungry 
one extends its arms as a fiilierman bis nets; it fpreads 
them every way, fo that they form a circle of confiderable 
extent, every part of which is entirely within the reach 
of one of them. In this expanded pofture it lies in ex¬ 
pectation of its food ; whatever comes within the verge 
of this circle is feized by one or other of its arms ; -the 
arms are then contracted till the prey is brought to the 
mouth, when it is foon devoured. While the arms are con- 
trading and exerting themfelves vigoroufly to counteract 
the efforts of the animal which it has feized to efcape, 
they may be obferved to fwell like the mufclesof the hu¬ 
man body when they are in a Hate of exertion. But the 
polype does not always wait for its prey ; it feels for it, 
and- in a manner follows it. It may be afked how can it 
perform this if deffitute of vifion ? or do the glandular 
grains anfwer the purpofe of eyes ? Who can anfvver the 
queftion ? what are our own eyes but glandular grains of 
a larger fize ? If this fhould be the cafe, our hydra, like 
the libelluls, and other inl'eds, would realize, nay, ex¬ 
ceed, the fables of the ancients, being an Argus entirely 
^compofed of eyes. Be this as it may, they are certainly 
in poft'effion of fome fenfation by which they are informed 
of the approach of their prey, and which renders them 
attentive to all that may confirm or deftroy this percep¬ 
tion. When the arms of a polype are extended within a 
glafs, put a centipe or any kind of worm into it, and 
with the point of a pin pulh it towards one of the arms ; 
as foon as it touches this, it is feized ; the worm or centipe 
endeavours by quick and ftrong efforts to dfiengage itfelf, 
Vol. X, No. 690. 
often fwimming and dragging the arm from one fide of 
the glafs to the other. This violent motion of the prey 
obliges the polype to contract ftrongly the arm 5 in doing 
which, it often twilts it in the form of a cork-fcrew, by 
which means it fhortens it more rapidly. The ftruggles 
of the devoted animal foon bring it in contact with ano¬ 
ther arm ; thefe contracting further, the little creature is 
prefently engaged with ail the arms, and by degrees con¬ 
veyed to the mouth, againft which it is held and fub- 
dued. See thefe different operations' exemplified in the 
HelminthoLogy Plate V. fig. 17, vol. ix. When a polype 
has nothing to eat, its mouth is generally open, but fo 
iinall, that it can fearcely be perceived without the aiTift- 
ance of a magnifying-glafs ; but, as foon as the arms have 
conveyed the prey to the mouth, it opens itfelf wider, 
and this in proportion to the fize of the animal that is to 
be devoured ; the lips gradually dilate, and adjuft them¬ 
felves accurately to the figure of the prey. The greatei! 
part of the animals on which the polype feeds, are, to its 
mouth, what an apple the fize of our heads would be to 
the mouth of a man. The worths or other minute ani¬ 
mals which are feized by the polype, are not always 
brought to the mouth in the fame iituation ; if they be 
prelented to it by one of their extremities, it is not re- 
quifite that the polype fhould open its mouth confiderably,. 
and in effect it only opens it fo wide, as precifely to give 
entrance to the worm. If it be not too long for the fto- 
mach, it remains there extended ; but if it be longer, the 
end which firlt enters is bent, fo that, wdien the worm is 
entirely fwallowed, it may be feen lying folded in the fto¬ 
mach. If the middle or any other part of the worm be pre- 
fented to the mouth of the polype, it leizes this part with' 
the lips, extending them on both Tides, and applying them 
againft the worm, fo that the mouth affumes the form of a- 
boat, pointed at each end. The polype gradually clofes- 
the two points of its boat-like lips, and by this motion 
and fudlion fwallows the worm. The polypes-kill worms 
fo fpeedily, that Fontana thinks they miift contain the 
raoft active and powerful venom ; for the lips of a polype 
fearcely touch the worm but it expires, fo great is the 
energy of the poifon it conveys into it, though no wound 
can be obferved in the dead animal. As foon as the fto¬ 
mach is filled, its capacity is enlarged, the body is fhort- 
ened, the arms are for the moft part contrafilecl, the po¬ 
lype hangs down without motion, and appears to be in a 
kind of ftupor, and very different from its fhape when 
extended 5 but in proportion as the food is digefted, and 
it has voided the excrementitious parts, the body lengthens, 
and gradually recovers its ufual form. The tranfparency 
of the polype permits us to fee diftindlly the worm it has 
fwallowed, which gradually lofes its form. It is at firlt 
macerated in the ftomach of the polype ; and, when the 
nutritious juices are feparated from it, the remainder is 
difeharged by the mouth. It is with thefe, as with other 
voracious animals, as they devour a great quantity of food 
at once, fo alfo they can faft for a long time. The hiftory 
of infefts furnilhes many examples of this kind.- 
One circumftance is obfervable, which probably con¬ 
tributes much to the digellion of their food, namely, that 
the aliments are continually pufhed backward from one 
extremity of the ftomach to the other; this motion»m;-y 
be eafily obferved with a microfcope, in a polype which 
is not too full, and in which the food has been already 
divided into fragments. For thefe obfervations, it is 
belt to feed the polype with fuch food as will give a live¬ 
ly-coloured juice; as for example, thofe worms whole in- 
teftines are rilled with red fubltances; for by thefe means 
we fliall fee that the nutritious juices are conveyed not 
only to the extremity of the body, but alfo into ths 
arms ; from whence it is probable that each of the arms 
forms alfo a kind of gut, which communicates with that 
of the body. Some bits of a fmall black fnail that is 
frequently to be found in our ditches, was given to a po¬ 
lype. The fubftance of this fkin was foon reduced into a 
pulp, co/ififting of little black fragments ; on examining 
1 T tks' 
