The blood is really salt. So is the sweat, as you can easily prove by putting your tongue anywhere on your skin, after you have been hot and sticky for a long time. And of course the tears are salt, as no doubt you found out long ago, sometime when everybody was especially horrid and they ran down into your mouth. In fact, pretty much everything about the body is salty, for the reason that it is all made of blood, which is itself pretty salt.

Now the blood is salt because the sea is. I much suspect that if the ocean had always been fresh water, like the ponds and lakes, then our blood, and the blood of all other animals, and all sweat and tears and the like, would have been fresh also. For the sea and the blood are salt with the same kinds of saltness. Their salt is mostly the sodium chlorid which we use for table salt, and besides these, there are calcium which makes limestone and lime and mortar and plaster, potassium which makes potash and soft soap, and various other metals including even gold. Altogether, sea water and blood are extraordinarily alike, especially when you consider that there are vast numbers of little animals in the sea that one can’t so easily tell from the white corpuscles of the blood.

The reason for all this is that the simpler creatures of the ocean do actually use the sea water for blood. Instead of having their bodies shut up tight as we land animals have ours, so that nothing gets into them unless we breathe or swallow, the inside of their bodies is open to the sea water, and the sea water flows in and out freely.

The sponges are like this. They take the water in through their smaller holes, and let it out through the large ones. They breathe the air that is in the water, and they turn their waste matter back into the water again, just as if the water were their blood. Many other creatures manage in this way, getting along without any private blood of their own, and using the great common ocean instead.

The rest of us have simply shut up our bodies and caught a little bit of the ocean inside. We call this bit of ocean, blood; and we have added various things to it. But still it is sea water, the same old sea water that is the blood of the earth and of all the lowly sea creatures that have no private blood of their own.

There are a great many other things also that we big land creatures have and do for no other reason than that some small sea creature began that way, and there has happened to be no special reason why anybody should change.

For example, all fishes, as you know, breathe by taking water in through their mouths and letting out again through a set of slits, usually five in number, at the side of what would be the neck if the fish had one. When the little fish is forming in the egg, at first it does not have any of these “gill slits” and so has to breathe through its skin. By and by, however, after the lower jaw has formed and there is a mouth, these slits punch through and become the convenient openings that we put a forked stick through when we go fishing and so bring home our fish, instead of putting them in our pockets, which is really a practice not at all to be commended.

So the little fish, while still in the egg, has these gill slits in the side of his head because later, when he gets hatched out and swims round, he is going to use them to breathe with. But the little chick in the egg, after his lower jaw has begun to grow, also has these same gill slits in the side of his neck, although when he hatches out, he is going to breathe with lungs, and is never going to have the least use for gills. So, too, do little puppies and kittens and colts and calves and all the land animals that breathe with lungs and haven’t the slightest use for any such holes.

Sometimes the hole doesn’t even break clear through. It starts from the inside and comes out, and from the outside and goes in, but the two tunnels never quite meet, and the hole never gets really open. But whether the holes open through or not, they soon close up again, and leave no sign that they have ever been there at all.

All except the first hole on each side, the one nearest the mouth. That never closes again, but remains open and becomes the hole into the ear. There is a hole in from the outside, as you know, the one you used to put beans and pencils in, only you oughtn’t. And there is another hole from the inside, beginning high up in the throat just where you can’t see it, and running in till it almost joins the other hole. Between the two is just a thin skin, which is the “drum” of the ear, and if you get a hole in it you may never be able to hear again. Because this drum never grew. It is the place that remained after one tunnel came in from outside, and another from inside, and the two didn’t quite meet.

So it comes about that all of us land creatures with backbones, who breathe with lungs, start making gill slits which we can’t possibly use. Then, because we have them on hand, we use the one farthest in front for the hole of the ear, and close the rest up again. And we take all that trouble—though it doesn’t trouble us much at the time—just because various other backboned creatures, which live in the water and don’t have lungs, had to make gill slits to breathe with.

There are a lot of things of this sort—parts and organs and members which one creature, while it is in the egg, makes and doesn’t use, just because some other creature, when it grew up, had to have them. You know what a short tail a hen or a turkey or a pigeon has—just a stub of a tail, only just big enough to stick its tail feathers in. But a little hen or turkey or pigeon, while it is still in the egg, has a tail like other animals, long enough to wag.

There is a kind of salamander, which is unlike most salamanders, efts, newts, and the like—these are all pretty much the same thing, and you find them almost anywhere in the brooks and the ponds and the damp woods. All of these that you are ever likely to see breathe with gills like a fish, and can live in the water. Only instead of having their gills covered over with a bony plate like the fish, these creatures often have them outside, like a sort of lace collar that hangs down at the side of their necks. Tom, the chimney sweep, in Charles Kingsley’s famous tale, after he turned into a water baby, had just such tufted gills so that he could swim under water like any newt or eft, and if you haven’t read “The Water Babies,” it’s certainly high time you did.

What I started to say is that this particular kind of salamander lives on the land. So he doesn’t need gills and doesn’t have them. But the little salamander, while he is still in the egg, has gills like any salamander, though for all the use he can ever put them to, he might just as well have been furnished with a pair of skates; for by the time he hatches out of the egg, the gills have been taken to pieces by his white corpuscles and the stuff used to make some other part of the body.

All the same, if you break open the egg, take the little creature out, and put him in the water while he still has gills, he will swim away, and live under water as well as any water creature. But if you wait till he hatches out of himself and has lost his gills, then if you put him in the water, he will drown just as you would. So the little salamander, that is going to spend his life on dry land, still has gills while he is in the egg and has no use for them, all just because other salamanders that live some of the time in the water need gills to breathe with.

Then there are the snakes, which have lungs and breathe air like any land animal. Only a snake is so very slender that there isn’t room in him for two lungs side by side. So he has only one proper lung, very long and thin, that runs from his neck pretty well down to his tail. Nevertheless, the snakes still keep the other lung, small and quite useless, tucked away beside the front end of the one they do use. Other reptiles have two lungs, so the snakes have to have two lungs also, though they can’t possibly use them both, and the other which they don’t use, merely takes up room.

We human beings are just as bad as the rest. Every little while, somebody comes down with appendicitis and has to be taken to the hospital to have his “vermiform appendix” taken out. The appendix isn’t the slightest use to anybody, we are better off without it, but in cows and dogs and rabbits and kangaroos, and various other animals, especially those that eat grass and leaves, it is a good deal of use for helping to digest food. So we have to have it, to be like the rest—and then pay the doctor to cut it off.

We don’t move our ears as horses and dogs and rabbits do. But still the muscles are there; and people say that anybody who wanted to take the trouble could learn to wag his ears like a baboon. Anyhow, the muscles are there, though we don’t use them and other creatures do.

We are said to have no fewer than one hundred and eighty such useless things about us—all sorts of little things that are no use to us at all and no use to half the animals that have them. But they are useful to the other half, and we all have to be in the fashion. Among these is a strange sort of single eye, set in the middle of the head, so that we really have three eyes instead of two. Our third eye is no bigger than a pea, and it lies tucked away between the two sides of the brain, well inside the skull, where it cannot possibly see anything. All the four-footed creatures have it. But in none of them is it the slightest use, except in certain lizards, especially in one in New Zealand, where it is a real eye placed in the middle of the forehead between the other two. Several American lizards also have this extra eye, though it isn’t good for much seeing, among them the “horned toad” of California, which of course isn’t a toad at all. So, just because a few lizards want three eyes to see with, the rest of the four-footed animals and we human beings have to have an extra eye that we don’t want, tucked away in pitch darkness inside our heads.

But that’s the way things are managed—salt blood, and gill slits, tails and gills in the egg and not out, extra lungs for the snakes, and extra eyes for us all, like Little Three Eyes in the story. It’s like the extra legs and tails on the lizard, and the extra heads on the planarian. Nature gets started making things, and doesn’t seem to be able to stop.