



Produced by Amy E. Zelmer





CORAL AND CORAL REEFS

by Thomas H. Huxley

[1]


THE subject upon which I wish to address you to-night is the structure
and origin of Coral and Coral Reefs. Under the head of "coral" there are
included two very different things; one of them is that substance which
I imagine a great number of us have champed when we were very much
younger than we are now,--the common red coral, which is used so much,
as you know, for the edification and the delectation of children of
tender years, and is also employed for the purposes of ornament for
those who are much older, and as some think might know better. The other
kind of coral is a very different substance; it may for distinction's
sake be called the white coral; it is a material which most assuredly
not the hardest-hearted of baby farmers would give to a baby to chew,
and it is a substance which is to be seen only in the cabinets of
curious persons, or in museums, or, may be, over the mantelpieces of
sea-faring men. But although the red coral, as I have mentioned to you,
has access to the very best society; and although the white coral is
comparatively a despised product, yet in this, as in many other cases,
the humbler thing is in reality the greater; the amount of work which is
done in the world by the white coral being absolutely infinite compared
with that effected by its delicate and pampered namesake. Each of these
substances, the white coral and the red, however, has a relationship to
the other. They are, in a zoological sense, cousins, each of them being
formed by the same kind of animals in what is substantially the same
way. Each of these bodies is, in fact, the hard skeleton of a very
curious and a very simple animal, more comparable to the bones of such
animals as ourselves than to the shells of oysters or creatures of that
kind; for it is the hardening of the internal tissue of the creature, of
its internal substance, by the deposit in the body of a material which
is exceedingly common, not only in fresh but in sea water, and which
is specially abundant in those waters which we know as "hard,"
those waters, for example, which leave a "fur" upon the bottom of a
tea-kettle. This "fur" is carbonate of lime, the same sort of substance
as limestone and chalk. That material is contained in solution in sea
water, and it is out of the sea water in which these coral creatures
live that they get the lime which is needed for the forming of their
hard skeleton.

But now what manner of creatures are these which form these hard
skeletons? I dare say that in these days of keeping aquaria, of
locomotion to the sea-side, most of those whom I am addressing may have
seen one of those creatures which used to be known as the "sea anemone,"
receiving that name on account of its general resemblance, in a rough
sort of way, to the flower which is known as the "anemone"; but being
a thing which lives in the sea, it was qualified as the "sea anemone."
Well, then, you must suppose a body shaped like a short cylinder, the
top cut off, and in the top a hole rather oval than round. All round
this aperture, which is the mouth, imagine that there are placed a
number of feelers forming a circle. The cavity of the mouth leads into
a sort of stomach, which is very unlike those of the higher animals,
in the circumstance that it opens at the lower end into a cavity of the
body, and all the digested matter, converted into nourishment, is thus
distributed through the rest of the body. That is the general structure
of one of these sea anemones. If you touch it it contracts immediately
into a heap. It looks at first quite like a flower in the sea, but if
you touch it you find that it exhibits all the peculiarities of a living
animal; and if anything which can serve as its prey comes near its
tentacles, it closes them round it and sucks the material into its
stomach and there digests it and turns it to the account of its own
body.

These creatures are very voracious, and not at all particular what they
seize; and sometimes it may be that they lay hold of a shellfish which
is far too big to be packed into that interior cavity, and, of course,
in any ordinary animal a proceeding of this kind would give rise to a
very severe fit of indigestion. But this is by no means the case in the
sea anemone, because when digestive difficulties of this kind arise he
gets out of them by splitting himself in two; and then each half builds
itself up into a fresh creature, and you have two polypes where there
was previously one, and the bone which stuck in the way lying between
them! Not only can these creatures multiply in this fashion, but they
can multiply by buds. A bud will grow out of the side of the body (I am
not speaking of the common sea anemone, but of allied creatures) just
like the bud of a plant, and that will fashion itself into a creature
just like the parent. There are some of them in which these buds remain
connected together, and you will soon see what would be the result of
that. If I make a bud grow out here, and another on the opposite side,
and each fashions itself into a new polype, the practical effect will be
that before long you will see a single polype converted into a sort of
tree or bush of polypes. And these will all remain associated together,
like a kind of co-operative store, which is a thing I believe you
understand very well here,--each mouth will help to feed the body and
each part of the body help to support the multifarious mouths. I think
that is as good an example of a zoological co-operative store as you can
well have. Such are these wonderful creatures. But they are capable not
only of multiplying in this way, but in other ways, by having a more
ordinary and regular kind of offspring. Little eggs are hatched and the
young are passed out by the way of the mouth, and they go swimming
about as little oval bodies covered with a very curious kind of hairlike
processes. Each of these processes is capable of striking water like an
oar; and the consequence is that the young creature is propelled through
the water. So that you have the young polype floating about in this
fashion, covered by its 'vibratile cilia', as these long filaments,
which are capable of vibration are termed. And thus, although the polype
itself may be a fixed creature unable to move about, it is able to
spread its offspring over great areas. For these creatures not only
propel themselves, but while swimming about in the sea for many hours,
or perhaps days, it will be obvious that they must be carried hither and
thither by the currents of the sea, which not unfrequently move at the
rate of one or two miles an hour. Thus, in the course of a few days,
the offspring of this stationary creature may be carried to a very great
distance from its parent; and having been so carried it loses these
organs by which it is propelled, and settles down upon the bottom of the
sea and grows up again into the form and condition of its parents. So
that if you suppose a single polype of this kind settled upon the bottom
of the sea, it may by these various methods--that is to say, by cutting
itself in two, which we call "fission," or by budding; or by sending out
these swimming embryos,--multiply itself to an enormous extent, and
give rise to thousands, or millions, of progeny in a comparatively short
time; and these thousands, or millions, of progeny may cover a very
large surface of the sea bottom; in fact, you will readily perceive
that, give them time, and there is no limit to the surface which they
may cover.

Having understood thus far the general nature of these polypes, which
are the fabricators both of the red and white coral, let us consider a
little more particularly how the skeletons of the red coral and of
the white coral are formed. The red coral polype perches upon the sea
bottom, it then grows up into a sort of stem, and out of that stem there
grow branches, each of which has its own polypes; and thus you have a
kind of tree formed, every branch of the tree terminated by its polype.
It is a tree, but at the end of the branches there are open mouths of
polypes instead of flowers. Thus there is a common soft body connecting
the whole, and as it grows up the soft body deposits in its interior a
quantity of carbonate of lime, which acquires a beautiful red or flesh
colour, and forms a kind of stem running through the whole, and it is
that stem which is the red coral. The red coral grows principally at
the bottom of the Mediterranean Sea, at very great depths, and the coral
fishers, who are very adventurous seamen, take their drag nets, of a
peculiar kind, roughly made, but efficient for their purpose, and drag
them along the bottom of the sea to catch the branches of the red coral,
which become entangled and are thus brought up to the surface. They are
then allowed to putrefy, in order to get rid of the animal matter, and
the red coral is the skeleton that is left.

In the case of the white coral, the skeleton is more complete. In the
red coral, the skeleton belongs to the whole; in the white coral there
is a special skeleton for every one of these polypes in addition to that
for the whole body. There is a skeleton formed in the body of each of
them, like a cup divided by a number of radiating partitions towards the
outside; and that cup is formed of carbonate of lime, only not stained
red, as in the case of the red coral. And all these cups are joined
together into a common branch, the result of which is the formation of
a beautiful coral tree. This is a great mass of madrepore, and in the
living state every one of the ends of these branches was terminated by
a beautiful little polype, like a sea anemone, and all the skeleton
was covered by a soft body which united the polypes together. You must
understand that all this skeleton has been formed in the interior of the
body, to suit the branched body of the polype mass, and that it is as
much its skeleton as our own bones are our skeleton. In this next coral
the creature which has formed the skeleton has divided itself as it
grew, and consequently has formed a great expansion; but scattered
all over this surface there were polype bodies like those I previously
described. Again, when this great cup was alive, the whole surface was
covered with a beautiful body upon which were set innumerable small
polype flowers, if we may so call them, often brilliantly coloured;
and the whole cup was built up in the same fashion by the deposit of
carbonate of lime in the interior of the combined polype body, formed
by budding and by fission in the way I described. You will perceive that
there is no necessary limit to this process. There is no reason why we
should not have coral three or four times as big; and there are certain
creatures of this kind that do fabricate very large masses, or half
spheres several feet in diameter. Thus the activity of these animals
in separating carbonate of lime from the sea and building it up into
definite shapes is very considerable indeed.

Now I think I have said sufficient--as much as I can without taking you
into technical details, of the general nature of these creatures which
form coral. The animals which form coral are scattered over the seas of
all countries in the world. The red coral is comparatively limited, but
the polypes which form the white coral are widely scattered. There
are some of them which remain single, or which give rise to only small
accumulations