Part 28

Still, I don’t know why any of these things are any more remarkable than that the lizard and hydra and earthworm and star-fish should have formed in the egg in the first place. That after all, is about the most remarkable thing there is in this world.

Not a few animals, moreover, in addition to having this power of mending themselves up after they have been injured, have also an arrangement for getting themselves hurt in a convenient place. The ray of a star-fish, for example, almost never breaks in halves. Whenever the ray gets caught so that it has to come off, it breaks close to the center, so that the whole arm comes off at once.

The crabs, such as one finds at the sea shore in salt water, have a special place in each leg, close up to the body, where the leg is meant to break off. The hard outer shell is turned back into the flesh and makes a round plate of shell with a hole in the middle, cutting right across the leg. Thru the hole run the nerves and blood vessels, but the muscles come to the plate on each side and there stop.

So when a hungry fish “catches a crab” by one leg, the crab digs his claws into sand or sea weed and pulls. The fish backs water with his fins and he pulls. Off comes the leg. Away goes the crab in safety. The leg has pulled off at this plate of shell. No muscle has been torn. The end of the stump is nicely protected; and all the injury that has been done is to the small thread of tissue no larger than a pin, which ran thru the hole in the center of the plate.

More than this, the stump is all ready to grow out again; and actually grows out quicker, after the leg has been taken off at this “breaking joint,” than if only a small piece had been taken off lower down. Such breaking joints, where the wound is all healed over before it is made, are somewhat common among animals, especially among those which have a jointed shell on their outside.

Even here, however, there are some queer doings. Sometimes, after a five jointed leg has been pulled off, the one which grows in its place, tho just as large and just as long, has only four joints. Some crabs, and the like, which have the big claws unlike on the two sides, if they lose either one, instead of growing one like it in its place, make a new claw like the one that belongs on the other side. Also, if they lose an eye, they grow a new one; but if they lose both the eye and the eye stalk on which the eye is set, then instead of an eye, they grow a small feeler. Really, one does not know which most to marvel at—their strange power of growing new parts, or their crazy way of growing them wrong.

But of all living repair shops the most uncanny are certain little flat worms, called planarians. These are a half inch or less in length, and fairly common in some places at the sea side, tho they are likely to be mistaken for snails which they much resemble.

Cut off the head of one of these creatures, and inside a week he will grow another—eyes, brain, mouth, and all as good as before. Cut off both head and tail, and still the creature will straightway fit himself out with new ones. Split him fairly in two lengthwise of the body, and each half will grow out a new half; and there will be two planarians, each complete, where only one was before.

Or if one splits the body in halves from the neck down, then each half body grows a new half, and there is a single head with two bodies. Or on the other hand, if one splits the head in two and leaves the body, each half head will become a whole one. Then we shall get a double headed planarian, a sort of Y-shaped creature.

Sometimes, after the planarian has been split in two from the neck backwards, and formed a Y upside down with two bodies and one head, another head, or occasionally two new heads, eyes, brain and all complete, grow out facing backwards in the fork of the Y. Indeed the animal seems to have a sort of mania for growing new heads and tails in all sorts of unbecoming places. If he gets a wound or cut almost anywhere in the body, and the wound happens to open on the whole backward, out of that wound or cut will grow a new tail in addition to the one he already has. But out of such wounds as face forward, there grow out complete new heads. As many as seven different heads have thus been made to grow on a single planarian—some on the middle of the back, some underneath the body, some even on the sides of the tail, and all, no doubt, greatly to the embarrassment of their owner.

As for cut off heads and tails, one might expect them to grow new bodies and become whole animals again. They do not, however, unless the pieces are pretty large. A head, cut off close behind the eyes, grows out, not a body, but another head. So all there is to the creature is two heads, joined neck to neck and looking in opposite directions.

All the time these things are going on, while the worms are making new heads, or bodies, or the two halves of one body are filling out again, the creatures can get nothing to eat. How then do they manage to grow? They live on their own flesh. The old fragment is taken down and used to build the new. An entire worm, made from a half worm, is no larger than the half from which it came. The animal, instead of growing large, grows small.

Whether it also grows young again, is by no means clear. Apparently it does. At least, a planarian that does not get enough to eat, proceeds at once to ungrow, becoming gradually smaller and smaller, till after a few months, it is no more than a fifteenth part of its former size. Whether it really becomes a baby worm again or not, it certainly looks like one, for it is a pretty small human baby that is not more than one fifteenth as large as a grown man.

XLVI

Little Monsters

One usually thinks of monsters as large. They are always, I believe, large and horrible in the fairy stories—giants and ogres and dragons and winged horses and chimeras and three-headed dogs and I don’t know what else, all most extraordinary to imagine as well as nice and creepy to read about. Really, however, there is no reason whatever why a monster should be large. It must be horrid, or unusual, or misshapen, or quite out of the ordinary. Then it is a true and proper monster, no matter how small it is. And as a matter of fact, some monsters, as strange as any maker of fairy stories ever invented, are too small to be seen at all, unless one looks for them with a microscope.

The planarian worms that I have just been telling about are monsters. If a two-headed calf is a monster, that people who go to the circus will pay to see, then surely a planarian is a still greater monster, with one extra head in the small of its back, another on the side of its tail, and four or five more hanging on at various places anywhere over its body; and this to say nothing of as many superfluous tails stuck on anywhere between. You know already that these monstrous planarians are formed because the worm, instead of healing up a cut as he should, seems possessed to grow a new head or tail out of it. I am going to tell you now how certain other strange monsters come to be.

You remember that earlier in this book, almost in fact, at the very first, I told you about how the eggs of all animals are, to begin with, single cells; and how afterwards, when they begin to grow, they split, first into two cells, then into four, then into eight, and so on, until finally, the single cell of the egg has become the hundreds and thousands which build the young animal.

Some of these eggs, especially those of certain of the small sea creatures such as star-fish and sea-urchins and the like, are extraordinarily tough. Indeed they have to be, else few of them would ever live to grow up at all. It is quite possible to take these eggs when the single cell has divided into two, and shake these two apart into two separate half eggs. You might think that each half egg would form a half animal. Instead, much like the planarian cut in halves, it forms a whole animal, half size.

Or we can wait till there are four cells, and shake these apart. Then we get four complete creatures, each quarter size. Or we can in the same way make eight. Beyond that we cannot go. Eight animals out of what was intended for one is all that egg can manage.

On the other hand, it is possible to take a half dozen eggs, which ought properly to have made as many separate creatures, and make them stick together into one gigantic egg, from which will hatch out a single gigantic animal, as large as the six or eight together which ought to have come from six or eight eggs.

Other strange things happen when the eggs, instead of growing in ordinary sea water, are put into water which has just a little bit more or less of something in it. For common sea water contains some half dozen different kinds of salt besides the one kind that people get out and use on the table and for cooking; and more or less of any one of these makes a salt water which is not quite the same as the salt water of the ocean. In fact, you must have noticed that salt water made with ordinary table salt does not taste by any means the same as ocean water.

A different kind of salt water (not very different either, I doubt if anybody could tell them apart by the taste,) sometimes makes a lot of difference with the creatures that grow in it. A little more of one thing, for example, makes little star-fish with their stomachs hanging out of their mouths, instead of inside their bodies where all proper stomachs belong. A little more of another, makes the sea minnows which live in it have only one eye, and that right in the middle of their foreheads like the single eye of the giant cyclops that I trust you have all read about long ago in the story of Ulysses. If you haven’t you certainly had better right away, for it is one of the great stories of the world, and has been told to children, and to grown men and women as well, for at least three thousand years, and nobody knows how much more.

Then again, by making things a little different in another way, the baby fishes grow like other proper fishes except that they do not have any hearts. Naturally, however, these particular monsters do not live to grow up. People make all sorts of strange creatures now-a-days by doing something to the young eggs when the new animal is forming.

Curiously too, all this sort of thing may happen to almost any egg by accident. If the two halves of the young egg get separated entirely, then the egg brings forth twin creatures so nearly alike that it is almost impossible to tell them apart at all. But if the two halves get only partly separated, the result is some sort of double monster.

So there are two-headed chickens, and two-headed snakes, and two-headed turtles, and two-headed calves. Sometimes only the tip of the nose is double. Sometimes it is the whole head. Sometimes there are two heads, four front legs, two hind legs, and one tail. Occasionally there is one body with eight legs, because the legs doubled and the body did not.

Just about as often, the doubling begins on the other end. Then there are two tails; or four hind legs and two front ones. Occasionally, two complete bodies are joined at one small region only They just missed being a pair of common twins It all depends on how well separated the first two cells of the egg happened to get.

The famous “Siamese Twins” were about like any other twins, except that they were fastened together side by side by a band of flesh under the arm. They lived to grow up, married, and travelled about the country exhibiting themselves for years. Finally one died; thereupon the other died almost immediately after. But as for that, any twins, if they are markedly alike, are likely to die at about the same time.