Chapter II: Part 2

Let us look first at some plants which have their home on the sand-hills. Here is a fine one, like a thistle, with stiff prickly leaves, and a stiff blue stem. In August it has blue-grey flowers. This plant is called Sea Holly, its leaves being like those of the holly. It has an unpleasant smell, yet its roots are used for making some kinds of sweets.

Now try to pull up a plant of Sea Holly. You find it no easy task. Then dig away the sand, and you see that its large roots have gone deep and far. All these plants of sandy places grow like that. Sand has no food or drink to give to plants. So they send their roots out, like plants in a desert, until they find what they want. Besides food and drink, they need a firm anchor in the loose sand. The Sea Holly, with its roots deep down and far-spreading, can hold its own, though the gale tears at it and throws its sandy bed here and there.

We pass many small creeping plants as we walk in the dry sand. There is a pretty Sea Convolvulus, with its stems deeply buried. It is a cousin of the common Bindweed. Then we see many plants of Thyme, and a few ragged bushes of Gorse. We notice that several little plants grow near the Gorse, as if they had crept there for shelter. The sea breeze has blown the sand into heaps, and even on these dry, thirsty hillocks we see many tufts of grass.

These Couch Grasses and Dune Grasses, as they are often called, are coarse and hard. Cattle pass them by in disgust. Yet they are the most useful plants on the shore. They can live and spread where other plants die. They have very long underground stems, which go through and through the dry, loose sand. The wind does its best to bury them in sand, but they send up hard, sharp buds, and go on living, and spreading.

Bit by bit, the sand is held together by the matted stems of these grasses. It becomes firm, instead of loose; the wind can no longer blow it about. Then other plants can grow in that place. You know how men go out to the wild parts of the earth and, by hard work, make those places ready for others to settle there. Well, the sand-grass works like that. It prepares the way for useful plants to grow in places where they could not grow before.

Quite near to the sea we shall find a very strange little plant. It has no leaves, only fleshy, jointed stems. It is known as the Glass-wort, being full of a substance useful in making glass. It belongs to a family which seems to delight in deserts and salty soil! They have all sorts of dodges to help them live in such places. For instance, their leaves are fleshy. Squeeze them, and they are like wet, juicy fruit.

The Sea Beet is also a member of this family. The Red Beet, as well as the Mangel-wurzel, we owe to this humble seaside plant. Most of our sugar comes from the Sugar-beet.

Another useful plant is the Sea Cabbage, which grows on some parts of our sea coast. It is rather a ragged, tough kind of Cabbage, and perhaps you would not choose it for your dinner-table. We have more tempting sorts in our gardens--Brussels Sprouts, Broccoli, Cauliflower, but long, long ago the wild seaside cabbage was the only one growing. Men found it to be eatable, and began to plant it near their huts or caves. From that small beginning all our garden cabbages have come.

Walking a little farther from the sea, we leave the sand and come to stones, rocks and cliffs. We pass a pretty plant, the Sea Lavender, and another, the Sea Stock. They love best the sandy, muddy parts of the shore. Their lilac flowers look bright and pretty. Coming to the rocky places, we find tufts of the flower known as Sea Pink or Thrift. Its leaves are like grass, and its flowers form a round pink bundle at the top of a bare stalk.

There are many tufts of Thrift growing among the rocks; and each tuft has a number of pink flowers. In some places you could step from one tuft to another for several miles. Bare and ugly stretches of coast are made into a gay garden by this lovely flower.

Here and there on the rocks is a plant with large yellow blossoms--the Yellow Horned Poppy. It is a handsome plant, and you are surprised to see such fine flowers among dry shingle, sand, or rock; but the Horned Poppy is well able to stand the salt spray and storms of its favourite home. When the petals have dropped, a green seed-pod is left. It is very long--nearly twice as long as this page and looks much more like a stem than a seed-pod.

Sometimes this seaside poppy is seen growing high up the face of the cliff, where only the jackdaw and sea-birds can find a footing; and many another plant may be seen there too. The cliffs are full of cracks, some tiny and some wide. In these places there is always a certain amount of dirt and grit. You could hardly call it "soil," and most plants would starve if you planted them in such a place.

These plants of the rock and cliff are not so proud. They have very long and very thin roots, admirably suited to pierce the grit, and explore the cracks in the rock, to find the moisture they need. Besides this, they have fleshy leaves which help them to keep alive. The Stone-crop and the Penny-wort are well-known plants of this kind. They grow where you would least expect to find a living plant. Neither heat nor thirst seems to kill them. Mother Nature has found many a wonderful way of helping her children to live.

EXERCISES

1. Why do plants which grow in sand have such long roots?

2. In what way are the grasses growing on the sand so useful?

3. Give the names of four flowering plants of the shore.

4. Where would you look for the Stone-crop and Penny-wort?

5. Why do these two plants have such thin roots?

LESSON VII.

FLOWER-LIKE ANIMALS.

The prettiest of the creatures of the shore is the Sea Anemone. No one can see it without being reminded of a flower, an Aster or Daisy, with a thick stalk and many coloured petals; but, knowing how it is made, and how it lives, we place it in the Animal Kingdom, though among the lowliest members of that Kingdom. It is a cousin of that strange creature, the Jelly-fish, which we shall look at in another lesson.

When the tide falls, you can walk among the rocks and pools by the sea, and find Anemones in plenty. They are fixed to the rocks. Some are under the ledges, out of sight, others are low down, half buried in the wet sand; and others are on the sides of the rocks, looking like blobs of green, brown, or red jelly. Feel one of them. It is slimy, and rather firm, not so soft and yielding as the Jelly-fish. You cannot easily pull it from the rocks without harming it; but you will find other Anemones on stones and shells; and these you can put in a jar of sea-water, with some weed, and carry home to examine later on.

When covered with sea-water the ugly blobs of jelly open out like beautiful flowers. In some places along our coast the floor of the sea is like a flower garden, gay with thousands of coloured Anemones.

Those little "petals" are really _tentacles_, used for catching and holding food. We will use a shorter word and call them feelers. They are set in circles round the top of the Anemone, and there are many of them. The Daisy Anemone, for instance, has over seven hundred feelers. Each feeler can be moved from side to side, and can also be tucked away, out of sight and out of danger; but, when hungry, the animal spreads them widely, for, as we shall see, they are the net in which it catches its dinner.

The whole body of the Anemone is like two bags, one hanging inside the other. The space between the two bags is filled with water. The feelers are hollow tubes which open out of this space; so they, too, are filled with water.

1. THE LARVA OF A LEAF-BODIED CRUSTACEAN CALLED PHYLLOSOMA.

2. A PRAWN-LIKE CREATURE, SHOWING THE FRONT LIMBS THAT ARE USED FOR GRASPING PREY.

3. A CRAB.

4. THIS IS A SHRIMP-LIKE CREATURE CALLED CUMA SCORPIOIDES.]

The Anemone can press the water into them, and so force them to open out. In rather the same way you can expand the fingers of a glove by forcing your breath into them. The Anemone, you see, can open or close just as it pleases.

What does it eat, and how does it find food? Perhaps you have watched an open Anemone in a pool, or in a glass tank, and seen it at its meals. A small creature swims near, and touches one of the feelers. Instead of darting away, it appears to be held still; and then other feelers bend towards it and hold the victim. Then they are all drawn to the centre of the Anemone, carrying their prey with them; and the feelers, prey and all, are tucked out of sight.

That is the way the Anemone obtains its food. As soon as the feelers get hold of a small animal they carry it to the opening of a tube in the centre. This is the mouth, leading to the stomach. Very often the feelers, with their victim, are tucked away into the stomach, and the feelers do not appear again for some time. Is not this a strange way of eating!

Much stranger still is the way in which the food is held, and made so helpless that it cannot escape. On the skin of the Anemone there are many thousands of very tiny pockets, or cells. Each cell contains a fine thread with a poisoned barb at the tip, The thread is packed away in the cell, coiled up like the spring of a watch. As soon as anything presses against the cells they shoot out their threads. Thus the tips of many poisoned threads enter the skin of any soft animal which is unlucky enough to touch an Anemone.

If your own skin is tender, these little stinging hairs will irritate it, but not enough to hurt you. It is different, however, with the small creatures of the sea. They are made quite helpless when caught by hundreds of these strange threads. We shall find similar poison-threads in the Jelly-fish; and these, in some cases, can cause us serious illness. You cannot see them without the aid of a microscope.

All those parts of its food which the Anemone cannot digest, it throws out again. If you feed an Anemone on raw meat, it tucks the pieces into its mouth, and, some days after, throws out the hard part of the meat, having taken all the "goodness" from it.

No doubt the Anemones themselves are eaten by other animals in the sea, but many kinds of fish will not touch them. You may remember that we noticed an Anemone which lived on the stolen home of the Hermit Crab. The crab lives in the whelk shell, and the Anemone lives on the roof, as it were. In nearly every ocean, all over the world, these two partners are found, using the same shell. It is thought that the Anemone lives there for two good reasons. First, the Hermit moves from place to place; you can see that this would give the Anemone a better chance of obtaining food. Also, bits of food float to the Anemone when the crab is picking his dinner to pieces.

The crab seems to like having his strange partner with him. No doubt the Anemone is of some use to him, or he would at once pull it off. It is thought that the Anemone protects him from his enemies, the fish. Some of them would swallow the whelk shell, crab and all, but they would not eat one on which an Anemone was fixed. We are not _sure_ that these reasons are the right ones. All we know for certain is, that a crab and an Anemone have, for some good reasons, gone into partnership.

Anemones have large families. Sometimes they have numbers of eggs; at other times their little ones come straight into the world as very tiny Anemones. A boy who kept a large Anemone in a tank of sea water, was astonished to find that in a short time, he had not one, but hundreds, of the creatures. The tiny Anemones were fixed to the glass and rock, all fishing for food with their little outspread tentacles. Sometimes the Anemone will calmly divide itself into two, each half becoming a perfect Anemone!

Anemones are of many shapes, sizes, and colours. The loveliest of our British ones is the Plumose Anemone. It is like a carnation, and may grow to be six inches high--that is, nearly as long as this page. It is known by its shape, not by its colour. It may be any of these colours--brown, deep green, pale orange, flesh colour, cream, bright red, brick colour, lemon, or pure white.

There are many other creatures in the sea which resemble plants and are often mistaken for them. The Sea Lily (p.49) is one of the flower-like animals; it is a relative of the Starfish, living in deep water. The Sea Mat (p.59) is often found on the shore. It seems like a horny kind of weed, but is really a colony of tiny animals, each one having its own little cell to live in.

EXERCISES

1. How does the Anemone expand its "feelers"?

2. In what way does the Anemone catch the small animals on which it feeds?

3. Where is the mouth of the Anemone?

4. In what way might the Anemone be of use to its partner, the hermit crab?

LESSON VIII.

SEA-WEEDS AND SEA-GRASS

We think of weeds as useless plants which insist on growing just where they are not wanted. So it is a pity that _Sea-weeds_ are so named, for the part they play in the sea is a useful one; and they are often beautiful, though they do not bear flowers like so many plants of the land. You see draggled heaps of them, lying on the shore where the waves have thrown them. They are best seen in their proper home, buoyed up by the water, and spreading out their broad coloured fronds, or long waving threads. There are, in many places, meadows of Sea-grass, and forests of Sea-weed! Mother Earth still has her carpet of green, even when covered by the salt water. The plants are very unlike those of the land, but, as you will see, they are of great use. We will suppose you put on a diving dress. Then you can walk out, under the water, and explore the forests of the sea.

Down by the line of low tide, before you have waded up to your knees, you find plants clinging to the rocks. They cover them with a slippery coat of green; when you turn these Sea-weeds over you find periwinkles and other animals feeding or hiding. Sea-weed makes good "cover" for the creatures of the rock-pools, who have many enemies to fear.

You notice that most of these shore weeds are green, sometimes as green as young grass. Pull up a bunch of the weed, and you find that it clings to the rocks and stones, but has no real roots. Seaweeds belong to a humble family in the world of plants, having no real roots, no flowers, and no real seeds. They can attach themselves to the stones or rocks. Along comes a great wave, and perhaps they are torn up; but this does not harm them, for they still live as they wash to and fro in the water, until they cling to another rock. Or they are thrown on the shore to die, or else to be washed back to sea by the next tide.

The Sea Lettuce or Green Laver is a common seaweed near the shore. Its broad, crinkled and bright green leaves are rather like those of a lettuce. Sometimes it is boiled to a jelly and used for food. Many other sea-weeds are good to eat, and on some coasts there is a regular sea-weed harvest.

Now wade into rather deeper water, and you find a great mass of the Bladder Wrack. Most schoolboys know it, for the little bladders of air in the leaves explode with a pop if you squeeze them. The Bladder Wrack, and others of the same kind, are torn up by the fierce waves in a storm, and tossed on the beach in heaps. They are gathered by the farmer who knows how to value a cheap manure for his fields. Some kinds are also of use in packing lobsters so that they come to market nice and fresh.

When you have walked--in your diving dress--to deep water, you find yourself among a tangle of olive-green weeds. They are below the line of low tide. All round you is a forest of dark-green ribbons with wavy edges. The ribbons are tough and very long, and cling tightly to the rocks. These ribbon-weeds, and others of the same kind, are known as Tangles. Round some parts of our coast they make wide, thick beds in the sea. Though the ribbons may be six feet long, they are not so wide as the palm of your hand.

Another sea plant, which grows in tufts in rather deep water, is called Irish Moss; it is green, brown or purple in colour. I do not know why it should be called Irish Moss, for it is not a moss, and it grows all round the English, as well as the Irish, sea-coast. But sea-weeds have strange names; indeed, many of them have no everyday names at all. Irish Moss is used for food, after being boiled to a jelly. It can also be made into a gum or glue, and has often been so used.

Now, if you were to walk still farther on the bed of the sea, into deeper water, you would find the prettiest of all the sea plants. These are the pink and red sea-weeds. You also find them on the beach, but only after they have been torn from their home in the deep water. They grow on the rocks, in pretty coloured tufts.

If you dive still farther, into the dark depths of the sea, you find beds of ooze and slime, and rocks and weird fishes, but no plants. Why is this? Like the land-plants, these sea-plants must have _light_. They cannot grow in the blackness of very deep water. Can you guess why some sea-weeds are green and others red? Those growing in the shallow water of the shore are green, like land-plants, because the sunlight reaches them. Only part of the light can pass through deep water; and so, in these shady places, the sea-weed is reddish in colour.

We see, then, that (1) green sea-weed grows by the shore; (2) brownish-green sea-weed likes deeper water; (3) red sea-weed grows in deep water; and (4) in very deep water there is no weed at all.

We must not forget the grass of the sea. It grows in narrow blades, often a yard in length, and as wide as your thumb. It is not a sea-weed, but a real flowering plant, which, for some reason or other, loves to grow under water. It creeps in the sand and mud, with green leaves growing up as thick as corn in a cornfield.

All these waving green leaves make large meadows in the sea; and sea-snails, fishes, and crabs hide in it, just as all manner of living things hide in the grass of our meadows. The proper name of this strange plant is Sea Wrack. When dried, it is useful for packing up china, and covering flasks of oil.

Now we come to the real use of sea plants. They are food for all the hosts of small animals of the sea. These eat it as it grows; or else, like the mussel and oyster, swallow the tiny scraps of it which float everywhere like so much dust.

The shell-fish, and other animals which feed on sea plants, are themselves eaten by other sea creatures, and these in their turn are eaten by crabs, lobsters and fish, which are eaten by us. It reminds you of a chain. The first link in the chain is the sea plant, the last links are the fish and ourselves. So, you see, the weeds and grass of the ocean are of very great value indeed.

EXERCISES

1. Give the names of three common Sea-weeds.

2. What is the colour of the weed found in deep water?

3. Why cannot Sea-weed grow in very deep water?

4. In what way are sea plants most useful?

LESSON IX.

THE JELLY-FISH.

Or all the queer children of Nature which live in the sea, the Jelly-fish is one of the queerest. You often find it on the shore, especially after a severe storm. There it lies, a mass of helpless jelly, which slips and breaks through your fingers if you try to lift it.

It cannot move back to its watery home, and in a short time the sun's warmth will have dried it up, leaving but a mark on the sand, and a few scraps of animal matter; for these strange creatures are little else but water. A Jelly-fish, which weighed two pounds when alive, would leave less than the tenth part of one ounce when dried!

There is a story of a farmer who, on seeing thousands and thousands of Jelly-fish along the shore, thought he would make use of them. He decided that they would serve as manure for his fields, and so save him much money. He went home, and sent men with wagons to be loaded with the Jelly-fish. This was done, and the Jelly-fish were spread over the soil. On looking at his fields the next morning, the farmer was astonished to find that every scrap of his new manure had vanished as if by magic!

In the sea the Jelly-fish looks like an umbrella of bluish-white jelly, from which hang tassels and threads. Look over the side of a boat, or from the pier, and you often see them drifting by, hundreds of them, like so many ghosts.

Each one is moving along, with its edges partly opening and shutting. It is plain that this waving motion causes the creatures to move through the water. Also, they can rise to the surface, or fall to the depths, and do not collide with one another. So the Jelly-fish is not at all helpless.

At night Jelly-fishes sometimes look very beautiful. Each one shines in the water, with a soft yet strong light, like fairy lamps afloat in the sea.

They are of all sizes. Some you could put in a small wineglass, others measure nearly two feet across. Evidently the Jelly-fish grows, and, in order to live and grow, it must eat; but what does it eat, and how does it obtain its food?

Before noticing the wonderful way in which this animal finds its dinner, let us look at its body. In any large Jelly-fish you can see marks which run from the centre of the body, and another mark round the edge of the "umbrella." These are really tubes. They all join with a hollow space inside the body, which is the creature's stomach. The mouth-tube opens under the body, as can be seen by turning the Jelly-fish on its back, and moving the lobes of jelly aside. All the food goes up this tube-mouth, and so into the stomach of the animal. The whole creature is little more than so many cells of sea-water, the walls of the cells being a very thin, transparent kind of skin.

Perhaps the strangest thing about it is the way in which it catches prey. Jelly-fish feed on all kinds of tiny sea animals, such as baby fish, and the young of crabs, shrimps, and prawns. These small creatures form part of the usual dinner of many a hungry dweller in the sea, and the Jelly-fish takes a share of them.

From the edge of the "umbrella" there hangs a fringe of long, delicate hairs, rather like spiders' threads. These are fishing lines, yet much more deadly. They trail through the water, stretching far from the main part of the Jelly-fish; and any small creature unlucky enough to touch them is doomed.

Down each one of these threads there are minute cells, hundreds and hundreds to every thread; and in each cell there is a dart, coiled up like the spring of a watch. The tip of the dart is barbed like a fishhook. Now the cells are so made that they fly open when touched. The dart then leaps out and buries itself in the skin of the animal which touched the thread. Not only that, but the darts are poisoned, and soon kill the small creatures which they pierce.

You see now how this innocent-looking Jelly-fish gets its food. As it swims along, the threads touch the tiny living things in the sea, the darts pierce them and poison them. Of course these stinging darts are very, very small, much too small for our eyes to see.

Sometimes there are numbers of large brownish Jelly-fish in the sea, or washed up on the shore. If you are paddling or swimming, keep well away from them. Their poison darts are able to pierce through thin skin, and may cause you illness and great pain. Remember that the threads are very long; after you have passed the main body of the animal, you may still be in danger from the trailing threads.

We noticed these same poison darts when we were dealing with the flower-like animals, the Anemones. Only, in that case, they were so fine, so small, that they had no power to harm us, even though they entered our skin. You may remember that we called the Anemone a cousin of the Jelly-fish, for they both belong to the same lowly division of the Animal Kingdom.

Animals have queer ways of getting a living. Who would expect to find millions of poisoned darts in a Jelly-fish? Who would guess that these weapons are coiled up, ready to spring out at their prey? Men have made many weapons for killing, from the bow-and-arrow to the torpedo, but none of them is more wonderful than the weapon of the Jelly-fish.

EXERCISES

1. Where is the mouth of the Jelly-fish placed?

2. How does the Jelly-fish move through the water?

3. What is the food of the Jelly-fish?

4. How does it obtain its food?

1. A FRESHWATER TURRET SHELL.

2. EDIBLE MUSSEL.

3. CONE SHELL.

4. SWORD-BLADE RAZOR-SHELL.

5. EAR SHELL, OR ORMER.

6. A TOP SHELL.

7. SCALLOP.

8. SWAN MUSSEL.]

LESSON X.

SHELLS AND THEIR BUILDERS (1).

THE PERIWINKLE, WHELK AND LIMPET.

Most of the shells which you find scattered over the shore are empty. The little animals which built them are gone; and their empty houses, of wonderful shapes and colours, are all that you find. Let us look at the builders of these pretty homes.

The shell-builders have soft, juicy bodies, and they are put in one big division of the animal kingdom--the _mollusca_, which only means _soft-bodied_. Some of these molluscs do not build shells. But most of them build a shelly house for themselves; they do this to defend their soft bodies from the attacks of a host of enemies. Some build two shells--the Oyster and Mussel do, as you know. These are called _bi-valves_; that is, two valves or shells; and others, like the Garden Snail, the Limpet, and Periwinkle, have one shell only, and so are called _uni-valves_.

The crab, and other _crustaceans_, also have a hard covering to their soft bodies; but it is not at all like the shell of a Snail, or other _mollusc_. The Snail's shell is like the little boy's suit which is altered and made bigger as the boy grows. The crab's covering is a suit which cannot be altered. It must be thrown away, and replaced by a larger one.

The body of the shell-builder is wrapped in a soft covering, a kind of outer coat, which is called the _mantle_. Now this mantle is one of Nature's cleverest inventions. It is able to take the substance called _lime_ from the food of the animal, and to use it as building stuff.

The shell is built to fit the soft body. When a Periwinkle is hatched from the egg, it is as big as a pin's head. It eats and grows, and the shell must therefore be made larger. So the mantle is stretched out, and it puts a film of lime to the edge of the shell. Bit by bit the shell is thus added to by the wonderful mantle. Look at a snail's shell, and notice the lines which show how many times the little house has been made larger.

Each kind of shell-builder has its own style of building. If you go to a museum and examine the shells gathered from all over the world, you are surprised at their wonderful shapes, markings and colours. Another surprising thing is their size. Some are enormous, so large that they make good washing-basins. Others are so small that you can hardly see them. Each one was made by the folds of the mantle of the animal that lived in it.

In our coloured pictures you see many different kinds of shells, some of them built by uni-valve molluscs and some by bi-valve molluscs.

Wherever there are weeds along the shore you can find whole armies of the Periwinkle--the "Winkle" we all know so well. It browses there, among the weeds, just as its cousin, the land Snail, browses on your cabbages. You must have seen the little door with which the Periwinkle closes the entrance to his house. The land Snail does not own a door, but he makes one when he goes to sleep for the winter.

The Periwinkle crawls on a broad, slimy foot, which is put out from the shell. It is stretched on this side or that, and so draws him and his home in any direction. There are two sensitive feelers in front of his head; and behind these are two short stalks, on each of which is a tiny eye. If alarmed, the Periwinkle can shorten his body, and pull it back into its shell, closing the entrance with the horny door.

But the strangest part of him is the tongue. It is not for tasting, but for rasping. It is like a long, narrow ribbon, on which are hundreds of tiny points, all sloping backwards. They are arranged three in a row. The Periwinkle rasps the seaweed with his tongue, and so scrapes off his dinner. Of course the teeth wear away.

But only part of the toothed ribbon is used at a time, so there are plenty of teeth behind the worn ones, ready to take their place.

The shell, as we have seen, is made of _limestone_. But the teeth are made _of flint_. This is a hard substance, so hard that it is used for striking sparks.

Now we will look at a shell-builder, the Whelk, who uses his flinty tongue in quite another fashion. The Whelk does not care for a vegetable dinner. He prefers to eat other molluscs--he is carnivorous, a flesh-eater; but these other molluscs do not wait to be eaten. As the enemy draws near they retire into their shells, and shut themselves up as tight as they can. The Whelk, however, is a clever burglar; he knows how to make a way into the hardest of shelly houses.

His front part--we might call it a nose--will stretch out to a fine point; and it contains a rasping tongue even harder than that of the Periwinkle. He sets to work. Moving the rasp up and down, he drills a neat round hole in the shell of the animal he is attacking. No shell is safe from him; and no tool could make a neater hole.

When you next gather shells on the beach, look at them closely; in some you will see where Mr. Whelk, the burglar, has been at work. He needs but a small entrance to enable him to suck out his helpless prey at his ease. Is it not strange that this creature, with a body as soft as your tongue, should earn its living by breaking into houses made of hard shell!

There are other molluscs which find their meals in this strange manner, and many others which, like the Periwinkle, feed more easily on seaweed. One of these, the Limpet, you can always be sure of finding at low tide; indeed, there are so many Limpets on the rocks that it would be hard _not_ to see them. You will know, if you have tried to force a Limpet from its hold on the rock, how very tightly it clings. It is as if the shell were glued or cemented by its edges.

Yet there is no glue or cement used, but only a simple dodge. The Limpet has a broad "foot," which almost fills up the opening of its shell. Like the foot of the Snail, it is used when the animal wishes to take a walk; but it serves another purpose too. It can be used as a sucker; and it is this which enables the Limpet to cling so firmly to its rock.

When the tide is out, the Limpet clings to the rock, its soft body tucked safely away in the shell. Its feeding time comes when the water covers the rocks once more. Then the Limpet's shell may be seen to tilt up, and a foot, and a head with feelers and eyes, come out. The Limpet crawls to the seaweed and begins to browse, using a rasp like that of the Periwinkle. It then crawls back to its own place on the rock. In time this resting-place becomes hollowed out, and the Limpet's shell fits into the groove thus made.

Limpets are useful as bait for fish. The Whelk and Periwinkle are gathered in immense numbers, and are used by us for food. Perhaps you have seen the egg-bundle of the Whelk. It contains many eggs when first laid in the sea. Each egg is as big as a pin's head. They swell in the water, until the yellowish bundle is three times as large as the Whelk that laid it. You often see the empty bundle blown by the wind along the shore.

EXERCISES

1. Give the names of two bi-valve molluscs.

2. What is the Periwinkle's shell made of?

3. Describe how the Periwinkle eats seaweed.

4. How does the Whelk obtain its food?

5. Give the names of three one-shelled molluscs.

LESSON XI.

SHELLS AND THEIR BUILDERS (2)

THE MUSSEL AND OYSTER.

As everyone knows, the Mussel and the Oyster live between two hinged shells. In the last lesson we called them _bi-valve molluscs_, which is only another way of saying "soft-bodied animals with two shells." Have you ever opened an Oyster? It is a tug-of-war, your skill and strength against the muscles of the animal inside the tight shells.

Like the Periwinkle and other shell-builders, these creatures owe their strong houses to a wonderful _mantle_; but in this case the mantle is in two pieces instead of one. You can imagine the Periwinkle's mantle as a tube enclosing the animal's body. The mantle of the Mussel or the Oyster is in two pieces; and each half forms its own shell.

The Snail, and other one-shelled molluscs, poke their heads out of the shell when feeding or moving. Oysters and their two-shelled cousins cannot do this, for the simple reason that they have no heads!

In some places you see that the rocks at low tide are covered with Mussels. In dense black masses they cling to the rocks; and, though heavy waves bang them like so many hammers, they stick tight. Little Mussels and big ones, they form a mass so thick that baby crabs and other creatures use them as a hiding-place. On the piers and groynes, and the woodwork of the harbour, you can see other clusters of Mussels; they are placed where the high tide covers them.

Have you noticed how the Mussel anchors himself? He uses a bunch of threads, like so many cables or tiny ropes. It is interesting to know how these threads are made.

The Mussel is, as a rule, a stay-at-home, but he can move from place to place if he likes. He has a long, slender foot which can be pushed out of the shells. Now the threads are fixed by the foot, just where the Mussel wishes to anchor himself. They are made from a liquid which forms in the body of the creature. This liquid hardens in the water so that it can be pulled out into long, fine threads.

Our ordinary Mussels do not make very long threads, but those of some kinds are so long that they can be woven into silky purses or stockings. The Mussel which makes such long anchor-threads might be called "the silkworm of the sea."

If the Mussel is such a stay-at-home, how does he find his food? The answer is, that the food comes to him, brought by the ever-moving water. There are countless specks floating in the sea, mostly specks of vegetable stuff. These settle on the floor of the sea, just as dust settles on our house-floors; and the waves wash this "sea-dust" hither and thither. The Mussel or Oyster, with shells gaping wide open, is bound to get some of this food with the water which enters the shells.

The Oyster has no "foot," and is fixed in one place nearly all its life. It is an interesting animal; and one of such value as food, that hundreds of thousands of Oysters are reared in special "beds," and sent to the market at the proper season. Our British Oysters were famous even in the time of the Romans; they were carefully packed and sent to Rome, and, at the Roman feasts, surprising quantities of them were eaten.

Many sea-animals have wonderfully large families, but the Oyster, with its millions and millions of eggs, beats most of them. Strangely enough, its eggs are not sent into the sea at once, but are kept between the Oyster's shells until they hatch. Needless to say, these babies are very small indeed, else their nursery could not contain them all Though so small that thousands of them together look more like a pinch of dust than anything else, yet each one has two thin shells; so that, if you eat the parent Oyster, they grate on your teeth like sand. Oysters, at this time, are "out of season"--that is, unfit for food.

At the right moment, the Oyster gets rid of its numerous family. It opens its shells, then shuts them rapidly; and, each time this happens, a cloud of young Oysters is puffed out like smoke. Now these mites must fend for themselves in a sea full of foes.

They have no defence, and countless numbers of them are gobbled up by crabs, anemones, and others. If this did not happen, the sea would soon be paved with Oysters.

For a time, the baby Oysters--which are known as "spat"--are able to swim here and there. In rough weather they are driven far into the deeps of the ocean, and lost. The rest of them, before they have been free for two days, settle on the bed of the sea--sometimes on their own parents; and there they remain for life. Only a very few out of each million become "grown-ups"--the rest are eaten by enemies, or smothered in mud or sand. In a year or so they are as big as half-a-crown. In five years they are fine, fat grown-up Oysters--that is to say, if they have not been dredged up from their bed and sent to market.

Their shells open and shut like a trap. You may have seen a picture of an inquisitive mouse trapped by an Oyster. Thinking to have a nice taste of Oyster, the mouse had poked its head into the open shells, but they were snapped together, and the mouse was firmly held in the trap.

Between the hinge of the two shells there is a pad, which acts like an elastic spring, and forces the shells open. The Oyster can close them by means of a strong muscle. They are its only defence, so it closes them at the least hint of danger.

Even these thick walls are sometimes of no avail, as we saw in our talk on "Five-fingered Jack." We saw how the starfish forces the shells open with the help of its strong tube-feet. The whelk and his cousins know how to bore a hole in the shell, and suck out the helpless Oyster. Then there are certain sponges, with the strange habit of making holes in shells, and living in and on them. Sometimes the Oysters are stifled in their "beds" by other Oysters settling and growing over them. Thick masses of Mussels may cling to them and suffocate them. And grains of sand sometimes get in the hinges of their shells, so that they cannot close up the house when they wish.

Like the other animals which are useful as food, Oysters have been carefully studied and cultivated by man for many, many years. The story of the Oyster-beds is a long and interesting one.

Oysters feed in rather a strange way. You may have looked inside the shells and seen two delicate dark-edged fringes, known as the "beard." This fringe is the Oyster's gills or breathing arrangement. Trace the "beard" as far as the hinge of the shells, and you see the mouth with its white lips. If you could watch the creature having its dinner, you would see a constant stream of water flowing over the gills and towards the mouth.

What makes the water move in that way? The gills are covered with very tiny lashes, like little hairs. There are so many of them that, as they keep moving, they force the water along, over the gills and towards the mouth. In this way the Oyster breathes the air which is in the water; but not only that. As we have already noticed, there is a kind of "vegetable dust" in the sea. This is driven to the Oyster's mouth and swallowed. The Oyster, fixed in its "bed," unable to hunt for food, thus makes its dinner come to it. What a strange use for a "beard"! It not only serves as lungs, but also helps the animal to catch its "daily bread"!

Another mollusc used as food is the Cockle, and its shell is one of the commonest found along the shore, especially near sandy places. It lives in sand, and can bury itself so quickly that you would have to use your spade with all your might in order to keep pace with this little shell-fish. Where Cockles have buried themselves you will see spurts of water and sand, showing where they are busy down below in the wet sand.

Besides being so skilful at digging, the Cockle is a first-rate jumper. If left on the beach, it jumps over the sand, towards the sea, in the funniest way. It is strange to see a quiet-looking shell suddenly take to hopping and jumping like an acrobat.

To perform this astonishing feat the Cockle makes use of its foot, which is worked by very strong muscles. It is large and pointed, and bent: if the Cockle wishes to move quickly, it stretches out its foot from between the shells, as far as it will go. Then, by using all its power, it leaps backwards or forwards in a surprising manner.

There are many other interesting molluscs, besides those we have looked at. The Piddock, or Pholas, is a smallish, rather delicate one, with a soft foot. But this foot is a most wonderful boring tool, fitted with a hard file. Hard rocks and wood are perforated by these little molluscs. Indeed, they are a positive danger, for they pierce the wooden piles of piers, and weaken them. They cannot pierce through iron, however, and so iron plates or nails are used to protect the piles from their onslaughts. You will often see stones and rocks riddled by the Piddock as if they were as soft as cheese. Chalk, sandstone, or oak, it is all the same to the Piddock, which rasps them away with its file. When the points of this strange instrument are worn out with all this hard wear, a new set takes their place.

EXERCISES

1. How does the Mussel anchor itself?

2. Describe how the shells of the Oyster are opened and closed.

3. What is the food of the Mussel?

4. Of what use is the "beard" of the Oyster?

5. Why is the Oyster called a bi-valve?

6. Why is the Oyster sometimes unfit for use as food?