Captain Basil Hall makes some interesting remarks on the examination of
a coral-reef, which is the product of the marine polypi. He observes
that, during the different stages of the tide, the changes it undergoes
are truly surprising. When the tide has left it for some time, it
becomes dry, and appears to be a compact rock, exceedingly hard and
rugged; but as the tide rises, and the waves begin to wash over it, the
coral worms protrude themselves from holes which before were invisible.
These animals are of a great variety of shapes and size, and in such
prodigious numbers, that, in a short time, the whole surface of the
rock appears to be alive and in motion. The most common worm is in the
shape of a star, with arms from four to six inches long, which move in
every direction to catch food. Others are so sluggish that they may be
taken for pieces of rock, and are of a dark color; others are of a blue
or yellow color; while some resemble a lobster in shape.
The GREEN POLYPE, or hydra, is found in clear waters, and may generally
be seen in great plenty in small ditches and trenches of fields,
especially in the months of April and May. It affixes itself to the
under parts of leaves, and to the stalks of such vegetables as happen
to grow immersed in the same water. The animal consists of a long,
tubular body, the head of which is furnished with eight, and sometimes
ten long arms, or tentacula, that surround the mouth.
It is of an extremely predacious nature, and feeds on the various
species of small worms, and other water animals, that happen to
approach. When any animal of this kind passes near the polype, it
suddenly catches it with its arms, and, dragging it to its mouth,
swallows it by degrees, much in the same manner as a snake swallows a
frog. Two of them may sometimes be seen in the act of seizing the same
worm at different ends, and dragging it in opposite directions with
great force.
When the mouths of both are thus joined together upon one common prey,
the largest polype gapes and swallows his antagonist; but, what is more
wonderful, the animal thus swallowed seems to be rather a gainer by the
misfortune. After it has lain in the conqueror's body for about an
hour, it issues unhurt, and often in possession of the prey that had
been the original cause of contention. The remains of the animals on
which the polype feeds are evacuated at the mouth the only opening in
the body. It is capable of swallowing a worm of thrice its own size:
this circumstance, though it may appear incredible, is easily
understood, when we consider that the body of the polype is extremely
extensile, and is dilated, on such occasions, to a surprising degree.
This species are multiplied, for the most part, by a process resembling
vegetation--one or two, or even more young ones emerging gradually from
the sides of the parent animal; and these young are frequently again
prolific before they drop off; so that it is no uncommon thing to see
two or three generations at once on the same polype.