Enter your search terms Submit search form

• Download pdf document

  (approx 17 pages)

• Download mobile pdf document

  (approx 87 pages)

CORAL AND CORAL REEFS

THOMAS H. HUXLEY

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.
...

• Download pdf document

  (approx 17 pages)

• Download mobile pdf document

  (approx 87 pages)