Natural Wonders

by Edwin Tenney Brewster

But what becomes of the severed tail end, if by any chance the robin fails to eat it up? That perhaps is the queerest thing of all. If the front part that crawled away is short, say a third of the animal or less, so that two-thirds of the worm at least is left in the tail piece, then this severed tail grows a new head. So the one worm becomes two. But if the tail piece is shorter, no more say than a half the whole animal, then that tail, instead of growing a head, grows another tail. In that case, the final result is one entire worm, old head end and new tail; and two tails, one old, one new, growing end to end. But of course, two tail ends, and nothing else cannot very well make a living, and, the worm soon dies of starvation.

There is, however, a smaller creature, the fresh water hydra, which quite outdoes the earthworm, when it comes to growing on new parts. The hydra is a very small sea-anemone, about as long as a pin is thick, with a long slender stalk and a circle of long fingers or tentacles round their mouths. One finds them growing on sticks and water plants almost anywhere in ponds.

Cut off one of these fingers, and it grows again. Cut the entire animal in halves as one chops thru the trunk of a growing tree, and the root end grows a new head, and the head end grows a new; root, and there are two new hydras in place of the one old one. Cut the animal into three pieces, head end, root end, and a small bit out of the middle of the stalk. The head end forms an entire new creature. The root end forms an entire new creature. The middle piece, which is neither head end nor root end, but just a little drum-shaped snipped out of the stalk between the two, even that grows a new root end and a new head end, and becomes an entire new creature, which in time grows to be as large as the one out of which it was made.

It is, in short, as if when one ripped off the sleeve of a coat, the coat grew a new sleeve; or when one pulled off the tail of the coat, the coat grew a new tail; while the severed sleeve and tail each grew new coats—pockets, buttons, collars, tails, sleeves, and all.

Our common star-fish, that we find in the salt water pools at the sea shore after the tide goes out, also isn’t at all bad at mending itself up after an accident. The five rays which grow out from its center are continually getting broken off. So one finds often in the water, star-fish with only four rays, or with four large ones, and one smaller one just growing out to take the place of one which has been lost.

But the lost ray, if something doesn’t eat it up, will grow a new star-fish. From the broken end, four more little arms bud out like those of a tiny star just getting its start in the world. The single arm or ray, not only grows out the other five, but in addition forms a new center for them to grow to, a new mouth, a new stomach, a new nerve ring round the mouth which is the creature’s brain; and so one thing with another forms a whole new star-fish with all its parts complete. And all the while, of course, the severed arm cannot eat anything, because it hasn’t any stomach. So it has to make the new parts out of the old, as the tadpole builds its new legs out of its old tail.

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.