THE MOLLUSCS
PLATE VII
THE CUTTLE (1 and 2)
We now come to the Molluscs, or Soft-bodied Animals, of which there are
a very great many. Some of them live in shells, like the oyster and
the whelk, and are often spoken of as “shell-fishes.” But they are not
really fishes at all, for they have no bones as fishes have, and are
made in quite a different way. And there are just a few of them which
have no shells at all.
One of these is that very curious creature which we call the Cuttle.
You may sometimes find it in the rock-pools, lurking in the crevices
among the rocks, or hiding under the masses of sea-weeds which grow
round the edges. It has a soft, white, bag-like body, and a big head,
on which are two great staring black eyes. Just above these eyes eight
long slender arms spring out; for cuttles keep their arms on their
heads instead of on their bodies! And another arm which is even longer
still, and is flattened out at the end into a kind of oval plate, hangs
down on either side.
All these arms are set with rows of round suckers, which are so
strong that if even a small cuttle catches hold of you, it will not
be very easy to make him let go. So if you do happen to find a cuttle
in a rock-pool it will be better to watch him in the water, without
attempting to catch him.
Down in the middle of all these branching arms, just where they spring
from the head, are two very curious organs. The first of these is the
beak, which is very strong, very sharp, and a good deal hooked. In
fact, it is rather like that of a parrot. The other consists of two
tubes which run downwards into the head, lying side by side together
like the barrels of a double-barrelled gun.
These tubes are called the “siphon,” and they are used for three
purposes.
First of all, they are used for breathing. The cuttle breathes water by
means of gills, like those of fishes, which lie inside the head; and
the water passes down to them through one of the siphon tubes, and then
goes out again through the other.
Next, they are used for swimming. When a cuttle wants to swim it
gathers all its arms together in front of its head, fills both its
siphon tubes with water, and then squirts their contents out again as
hard as it can. The result is that two jets of water come rushing out
of its head with such force that the surrounding water cannot give way
fast enough before them. So they push the cuttle backwards so swiftly
that if it were to dart across the pool you would hardly be able to
follow its movements.
The third use of the siphon tubes is a very strange one indeed.
Sometimes while you are looking at a cuttle in a rock-pool, the water
all round it will suddenly become quite dark, just as if a quantity of
ink had been poured into the pool. And so it has; for inside its body
the cuttle has a bag which contains a quantity of a deep black liquid
called “sepia.” This bag is surrounded by powerful muscles, and opens
into the siphon tubes; so that when the animal contracts the muscles,
the sepia is squirted out into the pool. It always does this if it is
frightened; and under cover of the darkened water it nearly always
succeeds in making its escape.
Inside its body the cuttle also has a very curious object which is
generally called a “cuttle-bone.” It is not really a bone, however, but
is made of almost pure chalk, and seems to act as a kind of support for
the bodily organs.
[Illustration: PLATE VII
1. THE CUTTLE.
2. THE EGGS OF CUTTLE.]
Another very odd thing about the cuttle is the way in which it lays its
eggs. These look just like purple grapes, and each has a small stalk,
by means of which they are fastened together in bunches. Indeed, the
fishermen always call them “sea-grapes.” You may often find them lying
about upon the beach in early spring, and if you open one of them
carefully, you will find a little baby cuttle inside it.
PLATE VIII
THE WHELK (1 and 2)
Everybody knows the shells of whelks by sight, and you can hardly take
a walk along the sea-shore without seeing hundreds of them lying about
on the beach. And great numbers of whelks are caught for human food,
and also to serve as bait for fishes.
One very curious thing about whelks is the way in which they lay their
eggs. Very often indeed, as you walk along the sandy sea-shore, you
will notice round clusters of yellowish white eggs, which often go
rolling along before the wind. Each of these clusters is about as big
as a cricket-ball, and the eggs of which it is made up are about as
large as peas. Now these are the eggs of whelks, and I think that every
one who sees them must wonder how these creatures can possibly manage
to lay such very big balls of eggs. For each egg-ball is at least two
or three times as big as the biggest whelk.
But, after all, the explanation is quite a simple one. When the eggs
are first laid they are very small indeed. Each is no bigger than a
tiny pin’s head. Instead of having shells, however, these eggs have
tough but very elastic skins; and these skins are made in such a way
that while they allow water to soak in from the outside, they will not
allow it to pass out again. So as soon as the eggs are dropped into the
sea they begin to swell; and the result is that before very long each
egg is as big as a good-sized pea.
If you pick up a cluster of these curious eggs in the early spring and
open them, you will find inside each the shell of a very tiny whelk,
which is almost ready to hatch out.
PLATE IX
THE DOG WHELK (1)
If you look in the ridges of small pebbles and bits of broken coal
which you will meet with here and there on the sandy parts of the
sea-shore, you are quite sure to find a number of very small whelk
shells. They are brownish yellow outside, and pinkish white inside, and
instead of being quite smooth, like those of the common whelk, they
are covered with a number of ribs which run down from the peak to the
margin. And these ribs are broken up in such a way that they look
almost like rows of beads.
[Illustration: PLATE VIII
1. THE WHELK.
2. THE EGGS OF WHELK.]
These are the shells of the Dog Whelk, and if you wait until the tide
is quite low, and then hunt about on the weed-covered rocks close to
the edge of the sea, you will very likely find some of the living
animals crawling about. They feed upon the sea-weeds by means of a
curious organ called the tooth-ribbon. This is just a narrow strip
of gristle, set with row upon row of very tiny hooked teeth; and by
drawing this backwards and forwards over the leaves of the weeds the
animal scrapes off very tiny pieces, which it then swallows.
In the tooth-ribbon of one of these whelks there are about a hundred
rows of teeth, with about nine teeth in each row: so that the animal
has nearly a thousand teeth altogether. But of course you can only see
them by means of a powerful microscope.
PLATE IX
THE STING WINKLE (2)
Although this creature is called a “winkle” it is really one of the
whelks. It is very common, and you may often find its empty shell lying
upon the shore. It is white, or yellowish white, in colour, and is
generally about an inch and a half in length, with several high ridges
running down it from the top to the bottom, and a number of smaller
ridges running crosswise between them.
You would not think that this could be a very dangerous creature, would
you? It looks as harmless as it can possibly be, and certainly you
need not be in the least afraid to pick up a sting winkle if you find
one crawling about, for it cannot injure human beings. But to other
shell-bearing molluscs it is a very terrible foe indeed. I dare say
that you have often noticed, when you have been picking up shells on
the sea-shore, that a good many of those shells had small round holes
bored through them. Well, those holes were pierced by a sting winkle.
For this animal is a creature of prey, and feeds entirely on other
animals which live in shells; and when it meets with one it fastens
itself to its victim’s shell, and drills a hole right through it by
means of its tooth-ribbon. It then pokes the tooth-ribbon through the
hole into the body of the animal inside, and draws it back again. As
it does so, of course, the sharp hooked teeth drag away little bits of
the animal’s flesh, which the sting winkle swallows. It then pokes its
tooth-ribbon down again into the body of the victim, and so on, over
and over again, until its hunger is satisfied.
PLATE IX
THE PERIWINKLE (3 and 4)
Of course you know the Periwinkle very well indeed by sight--and
very likely by taste, too! So there is no need for me to describe
it. But perhaps you did not know that there are two different kinds
of periwinkles. One of these is the Common Periwinkle, which is very
plentiful indeed on many parts of the coast. You may find it in
thousands and thousands if you hunt about on the weed-covered rocks
near the water’s edge when the tide is out, and no matter how many of
them are caught, there always seem to be just as many again next day.
This is the periwinkle which is used for food.
The other is the Dog Periwinkle. It is rather larger, and has a stouter
shell. If you want to find it, you must look on the rocks about
half-way between high and low water-marks, and there you will generally
find it crawling about in numbers. But it is not good for food, because
it often has a quantity of eggs inside its body, and inside these eggs
the shells of the baby periwinkles are already formed, which make it
dreadfully gritty. Thrushes, however, as well as a good many of the
shore birds, do not mind this in the least, and they devour so many of
both these kinds of periwinkles that it is quite a wonder that any are
left alive.
PLATE IX
THE PURPURA (5)
In size and shape this very common creature is rather like the dog
periwinkle. But its shell is white in colour instead of bluish black,
and generally has two or three bands of light yellowish brown running
round it. You may often find it crawling about on the weed-covered
rocks when the tide is out.
[Illustration: PLATE IX
1. THE DOG WHELK.
2. THE STING WINKLE.
3. THE PERIWINKLE.
4. THE DOG PERIWINKLE.
5. THE PURPURA.]
The purpura is quite a famous creature, because of the use which was
made of it by the ancient Romans. I dare say you know that in days of
old the colour of purple was very highly valued; and among the Romans
only members of the royal family were allowed to dress in purple
garments. Now this purple dye was obtained from the purpura. Inside its
body this creature has a little bag which contains about a drop of a
thick white liquid, rather like milk. Certainly it does not look in the
least like purple dye. But if you were to squeeze it out on to a sheet
of white paper, and to place it in the sunshine, you would very soon
see that it was changing colour. In a few minutes’ time it would
have turned to yellow. After a little time longer you would notice a
blue tinge creeping into the yellow, and turning it to green; and by
degrees the blue would become stronger and stronger, till the green
disappeared. At last a crimson tinge would creep into the blue and turn
it to purple; and this would be exactly the same as the famous purple
dye which the ancient Romans valued so highly.
The eggs which are laid by the purpura are very curious indeed, for
they are fastened down to stones by little stalks; so that each one
looks rather like an egg-cup with an egg inside it. And inside each of
these eggs are several little purpuras instead of only one.
PLATE X
THE SEA SNAIL (1)
This is one of the very commonest of all the shell-bearing molluscs.
You may find it crawling about in numbers all over the weed-covered
rocks which are left bare as the tide goes down. Its shell varies
very much in colour, for it is sometimes bright yellow, and sometimes
pale yellow, and sometimes olive green, and sometimes brown, and
sometimes almost black. Indeed, you might almost think that there were
half-a-dozen different kinds of these sea snails instead of only one.
These creatures have tooth-ribbons set with hundreds of tiny hooked
teeth, just like those of the dog whelks, and they use them in feeding
upon the leaves of sea-weeds in just the same way.
PLATE X
THE WENTLETRAP (2)
The Wentletrap is one of the most beautiful of all the shells which are
to be found upon the shore. Indeed, I really think that it is quite the
most beautiful. For the high ridges which stand out so boldly run round
and round it in the most graceful curves, and the whole shell looks
just as if it had been carved out of ivory.
[Illustration: PLATE X
1. THE SEA SNAIL.
2. THE WENTLETRAP.]
The wentletrap is sometimes known as the “staircase shell,” because the
ridges which run round it are very much like those spiral staircases
by which one climbs to the tops of church towers and other lofty
buildings. If you want to find it, the best place to look is in the
ridges of small pebbles which are washed up here and there on sandy
coasts by the waves, and which are generally mixed up with broken coal
which has been thrown out from passing ships. But it is not very
common, and you must not be disappointed if you do not succeed in
finding it.
PLATE XI
THE COMMON LIMPET (1)
This is a very common creature indeed, and you can find it in hundreds
and thousands on any rocky part of the coast. Numbers of its empty
shells are to be found lying about on the beach, and if you go down
among the rocks when the tide is out you will often notice that in some
places they are so covered with limpets that you can scarcely put the
tip of your finger in between them.
These animals cling to the rocks in the most wonderful way. Indeed,
if you take hold of a big limpet between your fingers you will not be
able to move it in the least, even if you pull at it and push at it as
hard as you can. But if you take the animal by surprise, and give it a
sharp, sudden blow sideways with a stone, or the end of a stout stick,
you can generally knock it off quite easily. And you will very often
find that a deep ring-shaped mark has been worn away in the rock by the
sharp edges of its shell.
However, limpets do not always remain clinging to the rocks, for they
can crawl about quite as easily as snails can, by means of that soft,
fleshy part of the body which we call the “foot.” And if you take them
home alive, and put them into an aquarium, you may often see them
creeping up and down the glass sides, through which you can examine
their bodies quite easily.
PLATE XI
THE KEY-HOLE LIMPET (2)
There are a good many different kinds of limpets, of which one of the
most curious is the Key-hole Limpet. It is generally found in rather
deep water, but you may sometimes find it clinging to the rocks just
above low-water mark. You must choose a season of “spring-tide,”
however, for then the tide goes farther out than usual, and leaves
behind it a good many creatures which at other times one hardly ever
sees.
The shell of this creature is rather stouter than that of the common
limpet, and has a number of ridges running down it from the peak to
the margin. Even by these you can tell it at once. But if you look at
it closely, you will also find that just at the top of the peak there
is a hole shaped rather like a key-hole. Through this hole the animal
squirts out the water which has passed over its gills; so that all the
time that it is breathing, if only one could see it, a kind of little
fountain is playing under water, spouting out from the top of its shell!
PLATE XI
THE SMOOTH LIMPET (3)
At first sight, perhaps, you would hardly take this creature for a
limpet at all, for it is ever so much smaller than either the common or
the key-hole limpets, and has a very thin and delicate shell indeed. It
varies a good deal in colour, but generally the shell is pale brown,
looking almost like polished horn, with eight or nine narrow streaks
of bright blue running down from the peak to the margin. It is often
called the “bonnet shell,” because in shape it is rather like an
old-fashioned bonnet.
You may often find the empty shells of this creature lying upon the
shore. But if you take them home you will find that as soon as they
become dry the beautiful blue streaks begin to fade, and that after a
few days you can hardly see them at all.
PLATE XI
THE CUP AND SAUCER LIMPET (4)
This is a very curious creature indeed. But if you want to see why its
rather odd name was given to it, you must look inside its shell instead
of outside. Then you will see that in the upper part is a curved plate
which really looks very much like a tiny tea-cup, while the shell
itself surrounds it just like a saucer. And if you were to examine the
animal which lives inside it very carefully, and to pull out its long
tooth-ribbon, you would find at the tip of it a curious little organ
which looks just like a tea-spoon. So that we have cup, saucer, and
spoon all in one!
Perhaps you may wonder what the odd little cup is for. Well, the fact
is that the muscles by means of which the animal clings to the rock are
very strong indeed. So, of course, there must be something else very
strong to which they can be fastened, and this cup-shaped plate gives
them a very firm hold.
The cup and saucer limpet is not a very common creature, and in many
parts of the coast it is never met with at all. But if you stay by the
sea-side on the south coast of England, you may sometimes find its
empty shell lying upon the shore.
[Illustration: PLATE XI
1. THE LIMPET.
2. THE KEY-HOLE LIMPET.
3. THE SMOOTH LIMPET.
4. THE CUP AND SAUCER LIMPET.]
PLATE XII
THE PAINTED TOP (1)
Tops are generally very common indeed on the sandy parts of the shore.
You cannot possibly mistake their shells for those of any other
creatures, for they are cone-shaped, looking very much like rather
flattened sugar-loaves, and are generally very beautifully coloured. So
pretty are they, indeed, that they are sometimes strung together and
worn as necklaces, or used for ornamenting ladies’ dresses.
The painted top is one of the most beautiful of all these shells, for
it is covered all over with spots and streaks and blotches of scarlet,
and crimson, and pink, and purple, and white, and blue, and yellow! But
all this lovely colouring is only on the outer coat of the shell, which
is very easily chipped off. The consequence is that these shells are
very often damaged by being tossed to and fro by the waves, and though
you may often find twenty or thirty in the course of a morning, not
more than two or three, perhaps, will be quite uninjured.
Tops are very useful creatures to have alive in an aquarium, for they
keep the glass sides clean from the tiny green weeds which so quickly
grow upon them. They do this by means of their tooth-ribbons, and you
may see them crawling about on the glass walls and mowing down the
weeds, just as a gardener cuts the grass on the lawn with his scythe.
PLATE XII
THE GREY TOP (2)
The painted top is rather a large shell, for it is often nearly an inch
in height from the peak to the margin. But the Grey Top, which is even
commoner still, is a good deal smaller. It is not nearly so brightly
tinted as the painted top, for it is yellowish grey in colour, with
zigzag black streaks running round and round it, which give it rather a
mottled look. Still, it is a very pretty shell indeed.
If you look at a top shell from underneath, you will always find that
there is a small hole in the bottom. This is the entrance to a passage
which runs right up into the peak of the shell. In the grey top this
hole is just about big enough to admit a rather fine needle.
PLATE XII
THE COWRY (3)
No doubt you have often found this very pretty shell, for on the sandy
parts of our coasts it is sometimes very common. You may often find
twenty or thirty cowries, indeed, in one of those ridges of pebbles and
small coal which are washed up by every tide. But if you were to see
the living animals crawling about I do not think that you would ever
guess what they were, for their soft bodies come outside their shells,
which they cover up so completely that you can hardly see them at all.
If you look on the upper part of the shell, you will see that a pale
streak runs across it from one side to the other. This streak marks the
line where the edges of the two sides of the body almost meet.
In some parts of the world cowry shells are used instead of money. It
seems rather an easy way of getting rich, doesn’t it, just to go and
pick up shells on the sea-shore? But then fifteen hundred of these
cowries are only worth about a shilling, so that you would have to pick
up a very great many even if you only wanted to do a day’s shopping!
And then they are ever so much bigger than our English cowries, so
that it would not be very easy to carry them about. You would have to
take several sacks full of cowries with you when you went to make a
purchase, instead of just keeping your money in a purse!
PLATE XII
THE CHITON (4)
The chiton is one of the oddest of all the shell-bearing molluscs;
for it does not look like a mollusc at all. It looks much more like a
kind of sea woodlouse, or a very tiny armadillo. For instead of having
a single shell like a whelk or a periwinkle, or a double one like a
cockle or an oyster, it has eight shelly plates on its back which
overlap one another, just like the tiles on the roof of a house. And if
you touch it, it will often roll itself up into a kind of ball, just
like the pill-millepedes, or “monkey-peas,” which are so common in our
gardens.
[Illustration: PLATE XII
1. THE PAINTED TOP.
2. THE GREY TOP.
3. THE COWRY.
4. THE CHITON.]
This creature is called the Chiton, and if you want to find it you
must go and look on the piles at the end of a pier, or on the rocks
which are left bare at very low tides. There you will often find it in
hundreds. Generally it is ashy grey in colour, but it varies a good
deal in hue, and you will sometimes find examples which are streaked
and mottled with pink, and orange, and white, and lilac, and chocolate
brown.
Before a chiton reaches its perfect form it passes through a kind of
caterpillar stage, and then turns into a sort of chrysalis, just as an
insect does. And both the caterpillar and the chrysalis, strange to
say, have eyes upon their heads, while the perfect chiton has none. But
some chitons have eyes all over their shells instead, and in some of
these very odd creatures between eleven and twelve thousand eyes have
been counted, the shells being almost entirely covered with them; so
that the animals may really be said to see with their whole bodies!