which are so many polypes growing from one trunk; whilst these are
developing, they also bud, which buds again put forth little ones, the
parent and the young ones forming a singular kind of animal society, in
which all participate of the same life, and the same wants. In this
state, the parent appears like a shrub thick set with branches. Several
generations are often thus attached to one another, and all to the
parent polype; after a time, this tree of polypes or hydræ is
decomposed, and gives birth to new generations, or fresh genealogical
trees. Here we see a surprizing chain of existence continued, and
numbers of animals naturally produced, without any union of sexes; every
polype raising a numerous posterity by a kind of animal vegetation.
From Fig. 16, Plate XXIII. B. the reader may form an idea of the
promptitude with which these creatures increase and multiply; the whole
group formed by the parent and its young was about an inch and an half
long, and one inch broad, the arms of the mother and her nineteen little
ones hanging down towards the bottom of the vessel; the animal would eat
about twelve monoculi per day, and the little ones about twenty among
them, or rather more than thirty for the group.
OF THE RE-PRODUCTION OF THE HYDRÆ.
So strange is the nature of this creature’s life, that the method by
which other animals are killed and destroyed becomes a means of
propagating these. When divided and cut to pieces in every direction
that fancy can suggest, it not only continues to exist, but each section
becomes an animal of the same kind.
A polype cut transversely or longitudinally, in two or three parts, is
not destroyed; each part in a little time becomes a perfect polype. This
species of fecundity is so great in these animals, that even a small
portion of their skin will become a little polype, a new animal rising
as it were from the ruins of the old, each small fragment yielding a
polype. If the young ones be mutilated while they grow upon the parent,
the mutilated parts are re-produced; the same changes succeed also in
the parent. A truncated portion will put forth young before it is
perfectly formed itself, or has acquired its new head and tail;
sometimes the head of the young one supplies the place of that which
would grow out of the anterior part of the trunk.
If a polype be slit, beginning at the head, and proceeding to the middle
of the body, a polype will be formed with two heads, and will eat at the
same time with both. If the polype be slit into six or seven parts, it
becomes a hydra with six or seven heads. If these be again divided, we
shall have one with fourteen; cut off these, and as many new ones will
spring up in their place, and the heads thus cut off will become new
polypes, of which so many new hydræ may again be formed; so that in
every respect it exceeds the fabulous relation of the Lernean hydra.
As if the wonders already related of the polype were not sufficient to
engage our attention to these singular animals, new circumstances, as
surprizing as the foregoing, present themselves to convince us of the
imperfection of our ideas of animality, and of the greatness of the
power of our LORD and SAVIOUR, who is the source and origin of every
degree of life, in all its immense gradations, as unity is the origin of
number in all its varied series, multiplied proportions and
combinations; and as numbers may be considered as recipient of unity, in
order to make manifest the wonderful powers thereof, so the universe and
its parts are adapted to receive life from the source of all life, and
thus become representatives of his immensity and eternity.
The polypes may be as it were grafted together. If the truncated
portions of a polype be placed end to end, and then pushed together with
a gentle force, they will unite, and form a single one. The union is at
first made by a fine thread, and the portions are distinguished by a
narrow neck, which gradually fills up and disappears, the food passing
from one portion to another. Portions not only of the same, 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 multiply like another.
There is still another method of uniting these animals together, more
wonderful in its nature, and less analogous to any known principles of
animation, and more difficult to perform. It is effected by introducing
one within the other, forcing the body of one into the mouth of the
other, and pushing it down so that their heads may be brought together:
in this state it must be kept for some time; the two individuals are at
last united, and grafted into each other; and the polype, which was at
first double, is converted into one, with a great number of arms, and
performs all its functions like another.
The hydra fusca furnishes us with another prodigy, to which we know
nothing that is similar either in the animal or vegetable kingdom. They
may be turned inside out like a glove, and, notwithstanding the apparent
improbability of the circumstance, they live and act as before. The
lining or coating of the stomach now forms the epidermis, and the former
epidermis now constitutes the coating of the stomach. A polype thus
turned, may often have young ones attached to its side. If this be the
case, after the operation they are of course inclosed in the stomach.
Those which have acquired a certain size extend themselves towards the
mouth, that they may get out when separated from the body; those which
are but little grown, turn themselves inside out, and by these means
place themselves again on the outside of the parent polype.
The polype thus turned combines itself a thousand different ways. The
fore-part often closes itself, and becomes a supernumerary tail. The
polype which was at first straight, now bends itself, so that the two
tails resemble the legs of a pair of compasses, which it can open and
shut. The old mouth is at the joint as it were of the compasses; it
cannot, however, act as one, so that a new one is formed near it, and in
a little time a new species of hydra is formed with several mouths.
Plate XXIII. B. Fig. 18, represents the upper part of a polype that has
been divided into two parts; a, the upper, c, the lower part, the end c
being something larger than that of a common polype, and is sensibly
perforated; in the summer time this part often walks and eats the same
day it is cut. Fig. 17, the other part of the same polype; the anterior
end is very open, and the edges of it turned a little outwards, which
afterwards folding inwards, close the aperture. This end now appears
swelled, as at c, Fig. 21; the arms shoot out from this end: at first
three or four points only begin to shoot, as at c, Fig. 20, and while
these increase in size, others appear between them; they can seize their
prey and eat before their arms have done growing. In the height of
summer the arms will often begin to shoot in twenty-four hours; but in
cold weather it will be fifteen or twenty days before the head is
formed. Fig. 22, represents a polype that was cut close under the arms;
this became also a complete animal in a little time.
The sides of a polype that has been cut longitudinally, roll themselves
up in different ways, generally beginning at one of the extremities,
rolling itself up in a heap, as in Plate XXIII. B. Fig. 19, with the
outside of the skin inwards; it soon unrolls itself, and the cut sides
form themselves into a tube, whereof the edges a b and e i, Fig. 15, on
both sides meet each other and unite. Sometimes they begin to join at
the tail end, at other times the whole sides gradually approach each
other. The sides join so close, that from the first moment of their
junction no scar can be discovered. Fig. 14, represents a polype partly
joined, as at i b, the part c a e not yet closed. Fig. 29, represents a
polype, the heads of which have been repeatedly divided, by which means
it becomes literally a hydra. Fig. 24, represents a polype that has been
turned, endeavouring to turn itself back again, the skin of the anterior
part lying back upon the other; the arms varying in their direction,
being sometimes turned towards the head, see Fig. 24 and 26, at others,
towards the tail. The anterior extremity c, formed by the edges of the
reversed part a, remained open for some days, and then began to close;
new arms shot out near the old ones, and several mouths were formed at
those parts where the arms joined the body. Fig. 23, 25, 27, 28,
represent the different changes that took place in another polype that
had been turned inside out, and the different revolutions it went
through before it acquired a fixed state; a c always shews the part the
polype had turned back, and a b the part it could not turn back.
A polype, which has been partly turned back, remains but a little time
in that situation. Fig. 28, a, the part where the portion it had turned
back joined to the body a b; this became straight, and formed a right
angle with a b; the same day another head appeared at e, and several
arms, a o, a n, began to shoot from the mouth a; at the other side of
this mouth there were the old arms a d. The next day the portion a c was
drawn near the body, and formed an acute angle with it, as at Fig. 25.
Fig. 27, represents the same swelled, after having swallowed a worm.
Four days afterwards its form had varied considerably, as may be seen by
comparing Fig. 25 and 28, having now one common mouth, and two small
polypes growing on it.
We may now be permitted to make a few reflections on this singular
animal. On considering the various properties that have been already
described, many particulars will be found in them that are very
analogous to others that are continually carrying on around us; we
perceive that there is a successive unfolding of new parts. In every
organized frame there is a continual effort to extend its sphere of
action, and enlarge the operation of that portion of life which is
communicated to it. This gradual evolution requires a secret and curious
mechanism, to regulate and modify by re-action the continued conatus of
the forming principle within it. The polype is an organized whole, of
which each part, each molecule, each atom, tends to produce another; it
is, if we may so speak, one entire ovary, a compound of germ, or seed.
In cutting a polype to pieces, the nourishing juices, which would have
been employed in supporting the whole, are made to act upon each
portion.
When a polype is divided longitudinally, it forms two half tubes; the
opposite edges of these approach, and in a very short time form a
perfect tube. The sides are made to touch each other by certain motions
and contractions of the piece; but as soon as the edges come in contact,
a slight adhesion takes place, the corresponding vessels unite, and new
ones are unfolded, as in a vegetable graft; by these means the points of
connection and cohesion are multiplied, the motion of the fluids is
re-established, and with them the vital œconomy. This is performed with
more rapidity than in vegetables, because the polype is nearly
gelatinous, and its parts are extremely ductile; this ductility is
supported and preserved by the element which it inhabits. The same
reasoning applies equally to explain the formation of so many heads to a
polype, as constitute it a real hydra.
A new polype is formed out of small portions or fragments, in a very
different manner, the operations in nature being always varied,
according as the circumstances differ; each fragment is puffed up, the
skin separated, and an empty space is formed within it; this part is to
become the stomach of the rising polype, which soon sends forth arms,
and is formed to the perfection proper to its kind. We learn from this
instance that the skin of the polype is not so simple as was at first
imagined; for we find it dividing itself into two membranes, and forming
thereby a cavity fit to perform all the functions of a stomach; but why
these membranes are separated in the small portions, and not in the
larger, we cannot tell; but though we are ignorant of this, and many
more circumstances relative to the re-production of these little
animals, yet the foregoing facts enable us to understand better the
nature of the existence of these polypes which have been turned inside
out.
For as that part which formed the interior skin of the stomach in the
little fragments before-mentioned, became the exterior part of the
animal, the inside of the polype is consequently so similar to the
exterior skin, that one may be substituted for the other, without
injuring the vital functions; from hence we might, in some measure, have
inferred the possibility of the polypes living, after they have been
turned inside out, independent of the fact itself.
The viscera of the animal are situated in the thickness of the skin, and
absorbing pores are placed both on the inside and outside, so that the
animal can live whether the skin be turned one way or the other. The
Author of nature did not create the polype to be turned as we turn a
glove; but he formed an animal whose viscera were lodged in the
thickness of the skin, and with powers to resist the various accidents
to which it was unavoidably exposed by the nature of its life; and the
organization necessary for this purpose was so constructed, that the
skin might be turned without destroying life.
Every portion of a divided polype has, like the vegetable bud, all the
viscera necessary to its existence; it can, therefore, live by itself,
and push forth a head and tail, when placed end to end against another
piece. The vegetation consists in uniting the portions, the vessels of
each part increase in length, and a communication is soon formed between
them, which unites the whole. The ease with which the parts unite, is as
has been observed before, probably owing to their gelatinous nature; for
we find many similar instances in tender substances. The solid parts of
the embryo, as the fingers, unite in the womb; tender fruit and leaves
may be also thus united.
A portion of these creatures is capable of devouring its prey almost as
soon as it is divided from the rest. In the structure of those animals
which are most familiar to us, a particular place is appropriated for
the developement and passage of the embryo. But on the body of an
animal, which, like a tree, is covered with prolific gems, it is not
surprizing that the young ones should proceed from its sides, like
branches from a tree. The mother and her young ones form but one whole;
she nourishes them, and they contribute to her existence, as a tree
supports, and is reciprocally supported by its branches and leaves.
OF THE HYDRA PALLENS.
The hydra pallens has been fully described only by M. Rösel;[113] it is
very seldom to be met with, is of a pale yellow colour, and grows
smaller gradually from the bottom, the tail is somewhat round or
knobbed, the arms are about the length of the body, of a white colour,
and generally seven in number, apparently composed of a chain of
globules; it brings forth the young from all parts of its body. Linnæus
defines it as, hydra pallens tentaculis subsenis mediocribus;[114]
Pallas as, hydra attenuata corpore flavescente, sursum attenuato.[115]
[113] Insecten Belustigung, 3. Theil. pag. 465. Tab. LXXVI. LXXVII.
[114] System. Nat. p. 1320, No. 4.
[115] Zoophyt. 4.
OF THE HYDRA HYDATULA.
Plate XXI. Fig. 1, 2, 3, and 4.
The next in order is the hydra hydatula, which we have already defined
from Linnæus as a hydra with four obsolete arms, and a vesicular body:
it is spoken of by several medical writers, who are enumerated in the
Systema Naturæ, p. 1321. It is described also by Hartman, Misc. Nat.
Cur. Dec. I. An. 7, Obs. 206, Dec. II. An. 4, Obs. 73, as hydatis
animata; also in the Dissert. de Inf. Viv. p. 50; n. 6, tænia
hydatoidea. Pallas defines it as tænia hydatigena rugis imbricata
corpore postice bulla lymphaticæ terminato. The following description is
extracted from that in the Philosophical Transactions, No. 193, by Dr.
Tyson, who names it lumbricus hydropicus.
In the dissection of a gazella or antelope, Dr. Tyson observed several
hydatides or films filled with water, about the size of a pigeon’s egg,
and of an oval form, fastened to the omentum, and some in the pelvis,
between the bladder of urine and the rectum; and he then suspected them
to be a particular sort of insect, bred in animal bodies, or at least
the embryos or eggs of them: 1. Because he observed them included in a
membrane, like a matrix, so loosely, that by opening it with a finger or
knife, the internal bladder, containing the serum or lympha, seemed no
where to have any connection with it, but would very readily drop out,
still retaining its liquor, without spilling any of it. 2. He observed
that this internal bladder had a neck or white body, more opake than the
rest of the bladder, and protuberant from it, with an orifice at its
extremity, by which, as with a mouth, it exhausted the serum from the
external membrane, and so supplied its bladder or stomach. 3. Upon
bringing this neck near the candle, it moved and shortened itself. Fig.
1, represents one of these watery bladders inclosed in its external
membrane, its shape was nearly round, being only a little depressed or
flatted, as a drop of quicksilver will be by lying on a plane. In Fig.
2, the neck is better seen; the external membrane being taken off, an
open orifice is found at its extremity; it consists of circular rings or
incisures, which are more visible when magnified, as in Fig. 3; it then
appears granulated with a number of little eminences all over the
surface; the orifice at the extremity seems to be formed by retracting
itself inwards, and upon trial it was found to be so; for in Fig. 4, the
neck of this polype is represented magnified and drawn out its whole
length; on opening it there were found within the two strings a, a,
which probably convey into the stomach the moisture and nourishment,
which the animal, by protruding its neck, extracts from the external
membrane.[116]
[116] Hydra hydatula habitat in abdomine mammalium, ovium, suum,
murium, &c. inter peritoneum et intestina. Vesica lymphatica,
pellucida, magnitudine pruni, petiolata corpore cylindrico, in cujus
apice os, quod, corpore compresso, movet tentacula vix manifesta.
Linn. Syst. Nat. p. 1321, No.5.
OF THE HYDRA STENTOREA.
Plate XXII. Fig. 27 and 28.
Hydra tentaculis ciliaribus corpore infundibuliformi.
The arms of this hydra are rows of short hairs, the body trumpet-shaped.
This species of hydra is very common, and has been described by almost
every writer on these subjects; it is placed by Müller among the
vorticellæ.
Vorticella stentorea caudata, elongata, tubæformis limbo ciliato. Müller
animalcula infusoria.
Mr. Baker originally named it the funnel-like polype, which Messrs.
Trembley and Reaumur changed to the tunnel-like polype, under which name
it appears in the Philosophical Transactions, No. 474.
There are three kinds of them, which are of different colours, green,
blue, and white. The white ones are the most common. It is necessary to
observe them often, and in various attitudes, in order to obtain a
tolerable idea of their structure. They do not form clusters, but adhere
singly by their tail to whatever comes in their way; their anterior end
is wider than the posterior, and being round, gives the animal somewhat
of a funnel form, though it is not completely circular, having a sort of
slit or gap that interrupts the circle. The edge of this opening is
furnished with a great number of fibrillæ, which by their brisk and
continual motions excite a current of water; the small bodies that float
or swim near this current, are forced by it into the mouth of the
little animal. Trembley says, that he has often seen a number of very
small animalcula fall one after another into the mouth, some of which
were afterwards let out again at another opening, which he was not able
to describe.
They can fashion their mouths into several different forms. If any thing
touch them, they shrink back and contract themselves. They live
independent of each other, swimming freely through the water in search
of their prey, and fix to any thing they meet with.
These animals multiply by dividing themselves, not longitudinally, nor
transversely, but sloping and diagonal wise; the proceedings in nature
continually varying in every new form of life. Of the two polypes
produced by the division of one, the first has the old head and a new
tail; the other, the old tail and a new head.
To make the description more clear, Trembley called that with the old
head the superior polype, that with the new head the inferior one. The
first particular that is observable in these polypes, when they are
going to divide, is the lips of the inferior one; a transverse and
oblique stripe indicates the part where it is going to divide; the new
lips are formed at about two-thirds of the length of the polype,
reckoning from the head; the division is made in a sloping line, that
goes about half way round the parent animal; these lips are at first
discerned by a slow motion, which engages the attention of the observer.
They then insensibly approach each other and close, whereby a swelling
is formed on the side of the polype, which is soon found to be a new
head. When the swelling is considerably increased, the two polypes may
be plainly distinguished. The superior one being now connected with the
inferior one only by its lower extremity, is soon detached from it, and
swims away to fix itself on some convenient substance; the inferior one
remains fastened to the place where the original polype was fixed before
the division.
From the various modes by which different species of polypes are
multiplied, we are led to form more exalted ideas of nature, and to see
that the little we discover is but an exceeding small part of her
contents; we learn also to be more cautious in reasoning from analogy,
and laying down the known for a model to the unknown, because we find
that the operations in nature are varied ad infinitum.
The growth of the hydra fusca is very quick, but that of the hydra
stentorea is much more so. The progress of the fœtus is always more
rapid than that of the infant and adult animal; but in these organized
atoms the evolution is so rapid, as to appear almost like an immediate
creation.
Fig. 28 represents the hydræ stentoreæ, or funnel-polypes, fixed to the
under side of a piece of some vegetable substance; they are in this
figure of their natural size.
Fig. 27, the same polypes magnified; the different forms they assume are
also seen here, sometimes short and thick, as at m m; long, as at n;
nearly globular, as at o; extended to the full size, as at k; seen as
contracted at i. The fibrillæ or little hairs may be seen in most of the
attitudes except those of l.
OF THE HYDRA SOCIALIS.
Plate XXI. Fig. 11.
Hydra socialis mutica torosa rugosa.[117]
[117] Linn. Syst. Nat. p. 1321. No. 7.
Social hydra, bearded thick and wrinkled.
This species of hydra has been described by many writers. It is the
vorticella socialis of Müller, who defines it as vort cella caudata,
aggregata, clavata; disco obliquo. Müller Animalcula Infusoria, p. 304.
Pallas makes it a brachionus, Pall. Zooph. 53.
In Fig. 11, these animals are represented as considerably magnified;
they appear like a circle, surrounded with crowns, or ciliated heads,
tied by small thin tails to a common center, from whence they advance
towards the circumference, where they turn like a wheel, with a great
deal of vivacity and swiftness, till they occasion a kind of whirlpool,
which brings into its sphere the proper food for the polype. When one of
them has been in motion for a time, it stops, and another begins;
sometimes two or three may be perceived in motion together. They are
often to be found separate, with the tail sticking in the mud. The body
contracts and dilates very much, so as sometimes to have the appearance
of a cudgel; at others, to assume almost a globular form. The young
polypes of this species have been sometimes taken for the hydra
stentorea.
OF THE VORTICELLÆ.
We now come to another division of these animals, to which later writers
have given the name of vorticellæ; this term I shall therefore adopt,
being of opinion that it behoves every man to maintain that order in
scientific arrangement which is not inconsistent with truth, except he
can produce another arrangement more expressive of the nature of the
objects it is designed to discriminate; a process requiring no small
degree of attention.