Day after day the forms of horses, dogs, birds, and other creatures pass
before our eyes. We look at them and call them by the names which we have
given them, and yet--we see them not. That is to say, we say that they
have a head, a tail; they run or fly; they are of one colour beneath,
another above, but beyond these bare meaningless facts most of us never
go.
Let us think of the meaning of form. Take, for example, a flower--a daisy.
Now, if we could imagine such an impossible thing as that a daisy blossom
should leave its place of growth, creep down the stem and go wandering off
through the grass, soon something would probably happen to its shape. It
would perhaps get in the habit of creeping with some one ray always in
front, and the friction of the grass stems on either side would soon wear
and fray the ends of the side rays, while those behind might grow longer
and longer. If we further suppose that this strange daisy flower did not
like the water, the rays in front might be of service in warning it to
turn aside. When their tips touched the surface and were wet by the water
of some pool, the ambulatory blossom would draw back and start out in a
new direction. Thus a theoretical head (with the beginnings of the organs
of sense), and a long-drawn-out tail, would have their origin.
Such a remarkable simile is not as fanciful as it might at first appear;
for although we know of no blossom which so sets at naught the sedentary
life of the vegetable kingdom, yet among certain of the animals which live
their lives beneath the waves of the sea a very similar thing occurs.
Many miles inland, even on high mountains, we may sometimes see thousands
of little joints, or bead-like forms, imbedded in great rocky cliffs. They
have been given the name of St. Cuthbert's beads. Occasionally in the
vicinity of these fossils--for such they are--are found impressions of a
graceful, flower-like head, with many delicately divided petals, fixed
forever in the hard relief of stone. The name of stone lilies has been
applied to them. The beads were once strung together in the form of a long
stem, and at the top the strangely beautiful animal-lily nodded its head
in the currents of some deep sea, which in the long ago of the earth's age
covered the land--millions of years before the first man or beast or bird
drew breath.
It was for a long time supposed that these wonderful creatures were
extinct, but dredges have brought up from the dark depths of the sea
actual living stone lilies, or _crinoids_, this being their real name. Few
of us will probably ever have an opportunity of studying a crinoid alive,
although in our museums we may see them preserved in glass jars. That,
however, detracts nothing from the marvel of their history and
relationship. They send root-like organs deep into the mud, where they
coil about some shell and there cling fast. Then the stem grows tall and
slender, and upon the summit blooms or is developed the animal-flower. Its
nourishment is not drawn from the roots and the air, as is that of the
daisy, but is provided by the tiny creatures which swim to its tentacles,
or are borne thither by the ocean currents. Some of these crinoids, as if
impatient of their plant-like life and asserting their animal kinship, at
last tear themselves free from their stem and float off, turn over, and
thereafter live happily upon the bottom of the sea, roaming where they
will, creeping slowly along and fulfilling the destiny of our imaginary
daisy.
And here a comparison comes suddenly to mind. How like to a many-rayed
starfish is our creeping crinoid! Few of us, unless we had studies about
these creatures, could distinguish between a crinoid and one of the frisky
little dancing stars, or serpent stars, which are so common in the rocky
caves along our coast. This relationship is no less real than apparent.
The hard-skinned "five finger," or common starfish, which we may pick up
on any beach, while it never grew upon a stem, yet still preserves the
radial symmetry of its stalked ancestors. Pick up your starfish, carry it
to the nearest field, and pluck a daisy close to the head. How interesting
the comparison becomes, now that the knowledge of its meaning is plain.
Anything which grows fast upon a single immovable stem tends to grow
equally in all directions. We need not stop here, for we may include sea
anemones and corals, those most marvellously coloured flowers of the sea,
which grow upon a short, thick stalk and send out their tentacles equally
in all directions. And many of the jelly-fish which throb along close
beneath the surface swells were in their youth each a section of a pile of
saucer-like individuals, which were fastened by a single stalk to some
shell or piece of coral.
We will remember that it was suggested that the theoretical daisy would
soon alter its shape after it entered upon active life. This is plainly
seen in the starfish, although at first glance the creature seems as
radially symmetrical as a wheel. But at one side of the body, between two
of the arms, is a tiny perforated plate, serving to strain the water which
enters the body, and thus the circular tendency is broken, and a beginning
made toward right and left handedness. In certain sea-urchins, which are
really starfishes with the gaps between the arms filled up, the body is
elongated, and thus the head and tail conditions of all animals higher in
the scale of life are represented.