adapted to shew the advantages of the microscope, which alone will
discover the peculiarities of its figure; this is so remarkable, that
entomologists appear undetermined as to its genus. Geoffroy formed a new
one for it, under the title of notoxus, in which he has been followed by
Fabricius; even Linnæus himself could not determine at first where to
place it, for in the Fauna Suecica he makes it an attelabus, but in the
last edition of the Systema Naturæ he has fixed it as a meloe, calling
it the meloe monoceros; but still he adds, “genus difficile terminatur
forte huic proximum.” Both Geoffroy and Schæffer have given figures of
it, but as they had not that kind of microscope which would assist them,
their figures are imperfect.
The head is black, and appears to be hid or buried under the thorax,
which projects forwards like a horn; the antennæ are composed of many
articulations, and with the feet are of a dingy yellow. The hinder part
of the thorax is reddish, the fore part black. The elytra are yellow,
with a black longitudinal line down the suture; there is a band of the
same colour near the apex, and also a black point near the base; the
whole animal is curiously covered with hair. Geoffroy says it is found
on umbelliferous plants: the one here described was found in May; the
natural size is seen at C.
Plate XIX. Fig. 1 and 3,
Represent two magnified views of the feet of the monoculus apus of
Linnæus. They are curiously contrived to assist the animal in swimming,
and form very agreeable objects for the microscope. Fig. 2 and 4 are the
same objects of the natural size.
OF THE SCALES OF FISH.
The outside covering or scales of fish afford an immense variety of
beautiful objects for the microscope. They are formed in the most
admirable manner, and arranged with inconceivable regularity and
symmetry: some are long, others nearly round, others again square;
varying in shape, not only in different species, but even considerably
on the same fish; those which are taken from one part not being entirely
similar to those which are taken from another.
Leeuwenhoeck supposed each scale to consist of an infinity of scales
laid one over the other; or, more simply, of an infinity of strata, of
which those next to the body of the fish are the largest.
These strata, when viewed with the microscope, exhibit specimens of
wonderful mechanism and exquisite workmanship. In some scales we
discover a prodigious number of concentric flutings, too fine, as well
as too near each other, to be easily enumerated; they are probably
formed by the edges of each stratum, denoting the limits thereof, and
the different stages of the growth of the scale. These flutings are
often traversed by others diverging from the center of the scale, and
generally proceeding from thence in a straight line to the
circumference.
Plate X. Fig. 7, exhibits a scale from a species of the parrot fish of
the West-Indies, considerably magnified. Fig. 8, the real size of the
scale.
Plate X. Fig. 9, is a magnified scale of the sea-perch, which is found
on the English coast. Fig. 10, the same scale of the natural size.
Plate XIX. Fig. 7, a scale from the haddock, as seen in the microscope.
Fig. 8, the same of the natural size.
Plate XIX. Fig. 9, a scale from a species of perch from the West-Indies,
magnified. Fig. 10, the scale of its real size.
Plate XIX. Fig. 11, a scale from the sole-fish, delineated as it appears
in the microscope; the pointed part is that which stands without the
skin, as may be seen in Fig. 5, which represents a piece of the skin of
a sole, as viewed by the opake microscope. Fig. 6 and 12, the same
objects of their real size.
CHAP. VII.
THE NATURAL HISTORY OF THE HYDRA, OR FRESH-WATER POLYPE.
Having in the two preceding chapters given the reader such a general
idea of the history and œconomy of a great variety of those minute
animated bodies, called insects, as I am inclined to hope has not only
afforded him entertainment and instruction, but tended to excite an
emulation for further researches; I shall endeavour to gratify so
laudable a disposition, by introducing him to a class of beings whose
œconomy and singular properties equally engage the attention of the
philosopher and the natural historian; a scene which opposes our general
system of vitality, and which presents to the eye of the mind, as well
as that of the body, a series of astonishing wonders. It is among the
minutiæ of nature that we find her models most diversified, and
displaying the marvellous fecundity of its powers.
The polypes described in this chapter are fresh-water insects, of the
genus of hydra, of the order of zoophytes, and class of vermes. The body
consists of a single tube, furnished at one end with long arms, by these
it seizes small worms, and conveys them to its mouth. It has, according
to our general notions, neither head, heart, stomach, nor intestines of
any kind; and is without the distinction of sexes, yet extremely
prolific. From the simplicity of its structure those of its œconomy and
functions are probably derived. When they are cut or divided into a
number of pieces, the separated parts in a very little time become so
many perfect and distinct animals; each piece having a power of
producing a head, a tail, and the other organs necessary for its
existence.
They are generally known by the name of polype; but as this was thought
by many to be improper, because that, strictly speaking, they have no
feet, Linnæus called the genus hydra, probably from their property of
re-producing the parts which are cut off, a circumstance that naturally
brings to mind the fabulous story of the Lernean hydra. Dr. Hill called
them biota, on account of the strong principle of life with which every
part is endued.
Leeuwenhoeck, whose indefatigable industry in his researches after small
insects permitted very few things to escape his notice, discovered these
animals, and gave some account of them in the Philosophical Transactions
for the year 1703. There is also in the same volume a letter from an
anonymous hand on this subject. We had, however, no regular account of
them, their various habits, their different species, or of their
wonderful properties, till the year 1740, when they first engaged the
attention of M. Trembley, to whose assiduity and observations we are
indebted for the display of their nature and œconomy.
Previous to the successful experiments of this gentleman, Leibnitz and
Boerhaave, as well as some of the ancient philosophers, reflecting on
the various gradations in the scale of animated nature, had endeavoured
to prove that there might be degrees of life between the animal and the
plant, and that animals might be found which would propagate by slips,
like plants. These conjectures were verified by Trembley, but not in
consequence of any pre-conceived ideas in favour of such a supposition;
on the contrary, it was only by repeated observations that he could
destroy his own prejudices, and join these wonderful beings to the
animal kingdom.[106]
[106] A great part of the knowledge of the ancients consisted in an
extensive variety of ingenious hypotheses, the result of intense study
and application; and it need not excite surprize, if, amongst a number
of suppositions, some of them have since been found conformable to
truth.
The moderns, animated by the example of the great Bacon, by an
abundance of experiments frequently repeated, and the assistance of
good instruments, have introduced unquestionable demonstration in the
place of speculation; this renders the present philosophy very far
superior to that of the ancients.
Thus it is with respect to the subject now under consideration; many
of the ancients conjectured that animated beings might exist possessed
of the wonderful properties of the hydra; that some of them, however,
were even witnesses of the fact, cannot well be disputed; though it
may be fairly presumed, that their knowledge of this animal,
comparatively with that we are now in possession of, was very
circumscribed and imperfect.
St. Augustine relates that one of his friends performed the experiment
before him, of cutting a polype in two, and that immediately the two
parts thus separated betook themselves to flight, moving with
precipitation different ways. The original passage is too long to be
here inserted, but may be found in his work “De Quantitate Animæ,” c.
62, p. 431, col. 1.
Aristotle, speaking of insects with many feet, expresses himself
nearly in the same manner; without naming the particular creatures to
which he alludes, he observes, that there are of these animals or
insects, as well as of plants and trees, some that propagate
themselves by shoots; and, as what were but the parts of a tree
before, become thus distinct and separate trees; so, in cutting one of
these animals, the pieces which before composed altogether but one
animal, become suddenly so many distinct individuals. And he adds,
that the soul in these insects is in effect but one, though multiplied
in its powers, as it is in plants. Aristot. de Histor. Animal. tom. 1,
lib. 4, cap. 7, pag. 824, & de Part. Animal. lib. 4, tom. 1, cap. 6,
pag. 1029. &c. This will suffice to shew that the ancients were not
entirely unacquainted with the subject before us; though it does not
derogate from the merit of Leeuwenhoeck, Trembley, and other ingenious
naturalists, by whose assiduous and patient investigations we have
obtained a more perfect knowledge of this astonishing class of
animated beings. EDIT.
Though natural history is so fruitful in extraordinary facts, it has
hitherto produced none so singular as the various properties of the
different species of the hydra.
I shall endeavour, first, to trace the progress of this discovery, in
which we shall see with what sage caution and accuracy Trembley, and
other naturalists examined this wonderful phænomenon, and what
accumulated evidence was judged necessary to establish the fact.
We find M. Trembley writing in January, 1741, to M. Bonnet, that he did
not know whether he should call the object which then engaged his
attention, a plant or an animal. “I have studied it,” says he, “ever
since June last, and have found in it striking characteristics of both
plant and animal. It is a little aquatic being. At first sight, every
one imagines it to be a plant; but if it be a plant, it is sensitive and
ambulant; if it be an animal, it may be propagated by slips or cuttings,
like many plants.” It was not till the month of March, in the same year,
that he could satisfy himself as to their nature.
When Reaumur saw, for the first time, two polypes formed from one that
he had divided into two parts, he could hardly believe his eyes; and
even after having repeated the operation an hundred times, and again
examined it an hundred more, he says that the sight was not become
familiar to him.
The first account the Royal Society received of the surprizing
properties of the hydra, was in a letter from M. Buffon, dated the 18th
of July, 1741, to Martin Folkes, Esq. their president, acquainting them
with the discovery of a small insect called a polypus, which is found
sticking about the common duck weed, and which, being cut in two, puts
forth from the upper part a tail, and from the lower end a head, so as
to become two animals instead of one. If it be cut into three parts,
the middlemost puts out from one end a head, and from the other a tail,
so as to become three distinct animals, all living like the first, and
performing the various offices of their species: which observations are,
adds Buffon, well averred.
There is no phænomenon in all natural history more astonishing than
this, that man, at pleasure, should have a kind of creative power,
and out of one life make two, each completely formed with all its
apparatus and functions, its perceptions and powers of motion and
self-preservation; and as complete in all respects as that from which
they derived their existence, and equally enjoying the humble
gratifications of their nature.[107]
[107] Goldsmith’s History of the Earth and Animated Nature.
Mr. Folkes, in confirmation of the foregoing article, communicated to
the Society a letter from the Hon. W. Bentinck, Esq. at the Hague, dated
September, describing the insects discovered by Trembley, adding, that
he himself had seen them. In November, a letter was read from Dr.
Gronovius, of Leyden, giving an account of a water insect not yet known
to, or described by any author; after describing it, he adds, “but what
is more surprizing, if this animal is cut into five or six pieces, in a
few hours there will be as many animals, exactly similar to their
parent.” The accounts of this animal were so extraordinary, that they
were not credited until Professors Albinus and Musschenbroeck were
provided with some specimens, and found all that had been related
thereof to be exactly true.
November 25, a letter from Cambridge was read to the Royal Society, in
which the author endeavours to lessen, by reason, the prejudices which
then combated the belief of these facts. “Some of our friends,” says
the author, “who are firmly attached to the general metaphysical notions
they have formerly learned, reason strongly against the possibility of
such a fact: but I have myself owned on other occasions, my distrust of
the truth, or certainty at least, of some of those principles, and I
shall make no scruple of acknowledging, that I have already seen so many
strange things in nature, that I am become very diffident of all general
assertions, and very cautious in affirming what may or may not possibly
be. The most common operations both of the animal and vegetable world,
are all in themselves astonishing, and nothing but daily experience and
constant observation can make us see without amazement an animal bring
forth another of the same kind, or a tree blossom and bear leaves and
fruit.
“The same observation and experience make it also familiar to us, that,
besides the first way of propagating vegetables from their respective
fruit and seed, they are also propagated from cuttings, and every one
knows that a twig of a willow particularly, cut off and only stuck into
the ground, does presently take root and grow, and become as real and
perfect a tree as the original one from which it was taken. Here then we
find in the vegetable kingdom quite common, the very thing of which we
have an example before us in the animal kingdom, in this new-discovered
insect. The best philosophers have long observed strong analogies
between these two classes of beings; and the more they have penetrated
into nature, the more they have extended this analogy: now in such a
scale, who is the man that will be bold to say, just here animal life
entirely ends, and here vegetable life begins? or, just so far, and no
farther, one sort of operation goes; and just here another sort, quite
different, takes its place? or again, who will venture to say, life in
every animal is a thing absolutely different from that which we dignify
by the same name in every vegetable?” Thus does the author endeavour to
persuade the prejudiced, and lead them to pay attention to the facts
which were now laid open to their view, and which were further confirmed
by a letter from M. Trembley, in January 1740; which letter was
strengthened by an extract from the preface to the sixth volume of
Reaumur’s history of insects. In March, 1742, Mr. Folkes gave an account
of them to the Royal Society, from observations made on several polypes
which had been sent by M. Trembley from Holland to him. The insects now
began to be known, and were soon found in England, and the experiments
that had been made on them abroad were published by Mr. Folkes,[108] my
father,[109] and Mr. Baker:[110] conviction now became too strong for
argument, and metaphysical objections gave way to facts. The animal is
described in the following manner:
HYDRA.[111]
Flos: os terminale, cinctum cirris setaceis. Stirps vaga, gelatinosa,
uniflora, basi se affigens.[112]
[108] Philosophical Transactions.
[109] Micrographia Illustrata.
[110] Natural History of the Polype.
[111] The hydræ or polypes have generally been denominated Insects: is
there not a manifest impropriety in the application of this term to
them? If we admit of the systematic arrangement of LINNÆUS, we find
that he has divided the animal kingdom into six classes: 1. Mammalia.
2. Aves. 3. Amphibia. 4. Pisces. 5. _Insecta_; and 6. _Vermes_. Of the
last or _Vermes_, the Zoophytes (from ζωοφυτον, or animal plant)
constitute the fifth order. He defines it as Animalia composita,
efflorescentia more vegetabilium: amongst these he includes the
various species of Vorticellæ and Hydræ.
The term animalculæ, or small animals, is certainly not inapplicable
to them, but they differ materially in the peculiar characteristics by
which insects are distinguished, see page 179, and pages 215-220. They
do not undergo those transformations to which insects are subject, and
which have been so fully described in the preceding part of this work:
their figure, habits, and œconomy are also very different. In short,
they seem to be in every respect, except their minuteness, quite a
distinct race of animated beings, as will be more fully exemplified in
the following pages. EDIT.
[112] Lin. Syst. Nat. p. 1320.
This animal fixes itself by its base, it is gelatinous, linear, naked,
can contract itself, and change its place. Its mouth, which is at one
end, is surrounded by hair, like feelers. It sends forth its young ones
from its sides, which drop off.
1. Hydra viridis, tentaculis subdenis brevioribus.
Green polype, generally with about ten short arms; it is represented in
Plate XXI. Fig. 5.
2. Hydra fusca, tentaculis suboctonis longissimis.
This polype has very long arms, often eight in number; it is represented
at Plate XXI. Fig. 7. The arms are several times longer than the body.
3. Hydra grisea, tentaculis subseptenis longioribus.
This polype has also generally long arms, in number about seven; it is
of a yellowish colour, small towards the bottom; it is represented at
Plate XXI. Fig. 6.
4. Hydra pallens, tentaculis subsenis mediocribus.
The arms of this polype are generally about six in number, and of a
moderate length.
5. Hydra hydatula, tentaculis quaternis obsoletis corpore vesicario.
Plate XXI. Fig. 1, 2, 3, 4.
This polype has a vesicular body, and four obsolete arms; is found in
the abdomen of sheep, swine, &c.
6. Hydra stentorea, tentaculis ciliaribus corpore infundibuliformi.
This polype has been called tunnel-shaped; the mouth is surrounded with
a row of hairs; it is represented at Plate XXII. Fig. 27 and 28.
7. Hydra socialis, mutica torosa rugosa.
Bearded, thick, and wrinkled. Plate XXI. Fig. 11.
OF THE HYDRA VIRIDIS, HYDRA FUSCA, AND HYDRA GRISEA.
Plate XXI. and XXIII.
These three species of the hydra having been those on which the greatest
number of experiments have been made, and of which we have the best
information, it is of these only I shall speak in the following account,
unless it is particularly mentioned otherwise.
There are few animals more difficult to describe than the hydra, as it
has scarce any thing constant in its form, varying continually in its
figure: they are often so beset with young, as to appear ramose and
divaricated, the young ones constituting as it were a part of the
parent’s body.
Whoever has looked with care at the bottom of a wet shallow ditch, when
the water is stagnant, and the sun has been powerful, may remember to
have seen many little transparent lumps, of a jelly-like appearance,
about the size of a pea, and flatted on one side; the same appearances
are also often to be seen on the under side of the leaves of those weeds
or plants that grow on the surface of the water; these are the hydræ
gathered up into a quiescent state, and seemingly inanimate, because
either undisturbed or not excited by the calls of appetite to action.
They are generally fixed by one end to some solid substance, at the
other end there is a large opening, round about which the arms are
placed as so many rays round a center, which center is the mouth.
They are slender and pellucid, formed of a tender kind of substance, in
consistence something like the horns of a snail, and can contract the
body into a very small compass, or extend it to a considerable length.
They can do the same with the arms; with these they seize minute worms
and various kinds of aquatic insects, bring them to the mouth, and
swallow them. After the food is digested, and the nutritive parts which
are employed in sustaining its life are separated from the rest, they
reject the remainder by the mouth.
The first polype which Trembley discovered was one of the hydra viridis,
represented in Plate XXI. Fig. 5. These are generally of a fine green
colour. The indications of spontaneous motion were first perceived in
the arms of these little creatures; they can extend or contract, bend
and wind them divers ways. Upon the slightest touch they contract
themselves so much, as to appear little more than a grain of a green
substance, the arms disappearing entirely. He soon after found the hydra
grisea, Fig. 6, and saw it eat, swallow, and digest worms much larger
than itself. This discovery was soon followed by that of the hydra
fusca, Fig. 7.
The most general attitudes of these hydræ are those which are
represented in Fig. 5 and 6 of the same plate. They fix the posterior
extremity _b_ against a plant or other substance, as _e f_; the body _a
b_; and the arms _a c_, being extended in the water. There is a small
difference in the attitudes of the three kinds which we are now
describing.
The bodies of the hydra viridis, Fig. 5, and of the hydra grisea, Fig.
6, diminish from the anterior to the posterior extremity by an almost
insensible gradation. The hydra fusca does not diminish in the same
gradual manner, but from the anterior extremity _a_, to the part _d_,
which is often two-thirds of the length of their body, it is nearly of
an equal size; from this part it becomes abruptly smaller, and goes on
from thence of a regular size to the end. The number of arms in these
three kinds are at least six, and at most twelve or thirteen, though
eighteen may sometimes be found on the hydra grisea. They can contract
their bodies till they are not above one-tenth of an inch in length;
they can also stop at any intermediate degree, either of contraction or
extension, from the greatest to the least. The species represented at
Fig. 5, are generally about half an inch long when stretched out. Those
exhibited at Fig. 6 and 7, are about three-fourths of an inch, or one
inch in length, though some are to be found at times about an inch and
half long. The arms of the hydra viridis, Fig. 5, are seldom longer than
their bodies; those of Fig. 6 are commonly one inch long, while those of
Fig. 7 are generally about eight inches; whence Trembley has called it
the long-armed polype.
The bulk of the hydræ decreases, in proportion as they extend
themselves, and vice versa. They may be made to contract themselves,
either by touching them, or agitating the water in which they are
contained. They all contract themselves so much when, taken out of the
water, as to appear only like a little lump of jelly. They can contract
or extend their arms without extending or contracting the body, or the
body, without making any alteration in the arms; or they can contract or
dilate only some of the arms, independent of the rest: they can also
bend their body and arms in all possible directions. Those represented
at Fig. 7 let their arms in general hang down, making different turns
and returns, often directing some of them back again to the top of the
water. They can also dilate the body at different places, sometimes at
one part, and then again at another; sometimes they are thick set with
folds, which, if carelessly viewed, might be taken for rings.