LESSON XL.
THE STAR-FISH WITH AN OVERCOAT.
There is a very pretty star-fish called the Sea-Egg, or Sea-Urchin. This creature has not five points or rays; it is in the shape of a ball, somewhat flattened.
Fig. 1.Fig. 2.Fig. 3.
Fig. 1.Fig. 2.Fig. 3.
Do you say, “Can this belong to the Star-fish Family, when it has no rays?” Well, let us see. Let Figure 1 represent our Ray pattern. Bend the rays up, and the plan looks like Figure 2. Then bend them until the tips touch, and you have the form of Figure 3. The cover of this star-fish, called the sea-urchin, is not tough and skin-like; it is hard and shell-like.
If you look at it, you will see that it has up and down it lines of knobs and dots set in double rows. You will find five double lines of large knobs, and as many lines of small dots between the larger ones.
Do not think that you can see these marks as soon as you find a sea-urchin. By no means! The sea-urchin wears a fine thick overcoat, which hides his shell.
Well Dressed.
Well Dressed.
I knew a boy who found a number of sea-eggs lying on the beach. He cried out, “Oh! look at all the chestnut burrs in the water!” The sea-egg when it is alive looks much like a chestnut burr, ripe, but not open. It is covered all over withthorns or prickles like the burr, and the water gives it the dark brown color.
Now let us look into this matter. You have read that a cross-star-fish has along the under edges of its rays many little tubes full of something like water. He can move them, and upon them he walks.
Undressed.
Undressed.
The sea-urchin has hard, sharp spines, which cover all the shell, and look like a rough coat. In the pictures you see the urchin with his shell bare, with his shell half bare, and with his full overcoat of quills. When the shell is bare, you will see upon it little lines of points or knobs. These are very pretty, but they are for use, rather than for beauty.
On every tiny knob is placed a spine, and the urchin can turn and move his spines, in all directions, just as easily as you can move your arm at the shoulder-joint.
When the urchin is alive, the quills stand out all about him. After he is dead, the quills drop off.
Between the rows of knobs are five double rows of holes, like pin-pricks. Out of these grow such little suckers as I told you the star-fish had.
In some countries the sea-urchins are small—not much larger than a dime. In warmer seas the urchins grow large, even as large as a large orange. People often use these larger ones for food.
The sea-urchin walks on his spines, as the cross-star-fish does on his. But as the quills of the urchin are all around him, like a ball-cover, his walk is a roll! By the little suckers he can cling to the rocks, and he can climb up their sides.
Turn over the bare urchin shell, and you will see that while at the top it has no opening larger than a pin-prick, on the under side there is a hole where the curved rays do not come entirely together. You see the urchin must have this open place for his fish-lines, and to put food into his ever-hungry mouth.
Since the sea-urchin eats so much, he must grow! Does he?
Yes, the sea-urchin grows, and it cannot cast its shell as a crab can. It has not a soft skin as you have, yet his shell is never too tight. How can the shell expand as the urchin grows?
The shell is made up of a great many little plates, or scales. As the urchin within grows and needs more room, these little scale-plates grow larger all around.
Here is a strange thing: these wee plates are set like bricks in a dome. You know the urchin is made on the five-ray pattern bent like a flattened ball.
About the body of the urchin, within the shell, is wrapped a soft, pretty, silk-like mantle. This mantle lines the shell. It takes lime from the sea-water and builds it into more shell along the five edges of these wee plates. It also adds new plates.
So, as the urchin keeps growing all the time, its mantle is building upon the plates all the time. The house or coat, whichever you choose to call it, grows with the growth of its owner. I think your mother would be glad if she could find you a coat to grow with the growth of your body.
The shell part of the urchin is gray or greenish gray. The quills are often red, brown, pink, orpurple. When a number of these urchins are fast upon a rock, they look like a bed of lovely fringed flowers.
The urchins are able to bore holes even in the hard limestone rock. They bore these holes to live in, and, as they grow, they make the holes larger, but not the openings. So, after a time, they are shut into a prison which they have dug for themselves. They do not do this on our coast.
On the coast of Spain you will find the rocks covered with these urchins, fixed in holes. No doubt they feel that stone walls are safe walls. If they had wished to get away, and go and come freely, I think they could have made their doorways as large as themselves.
There is much more to be learned about sea-urchins. You will do well to study them when you can. In fact, the longest life is not long enough in which to learn even what is to be learned of very simple and common things. There is danger that when we have learned a little we shall become proud, and that we shall not take the trouble to learn the very much more which we do not know.