SOME animals have their hard parts on the outside. These may be a horny coat or skin, such as the beetle has, or a double shell, like the oyster's, or a single shell, like the house of a snail. Or they may be a hard crust, like the lobster's coat of mail, or a brittle crust, like the sea-urchin's, or with tough nodules on a leathery hide, as in the star-fish, or any one of a hundred variations from these. But in all such cases there is no backbone, no true skeleton and no real skull.

Then there are a host of animals that have their hard parts on the inside. When this is the case the animal has a regular head, generally with a skull inside to protect a brain from hard knocks.

Then behind the skull is a backbone made up of a number of separate joints of bone. To the skeleton other bones are :attached to help the animal to move himself about on land or in the water. Sometimes these bones grow out as legs, with toes and claws at the tip of them. Sometimes they take the form of wings or they may spread out into flat paddles or oars of one kind or another, and these we call fins. What shape the parts take depends on what the animal does with them, for every kind of beast is built with direct reference to his business in life.

The back boned animals are the highest of all the animal kingdom. That is, in general; they can do more things, they have a greater variety of relations to the things around them, and they are more definitely fitted for a high position. Some of them are not very high nor very intelligent, even as compared with their lower brethren, the insects. The ant is a tiny creature, with no skull and no backbone, and cannot do any very big thing. But she is a very wise beast by the side of a carp or a herring. Still, on the whole, the back boned animals are the highest and as you and I both belong to that class we could never afford to confess to any doubts as to their superiority.

But we are the highest of the type that is, we men — and the rest of the tribe are all lower. And the lowest of all back boned animals we call fishes. And we shall know a fish when we see one because the hard parts or skeleton are on the inside, and he stays in the water, breathing the air which is dissolved in it, and he has never any toes or claws or feathers.

He breathes with gills and he swims with fins. He has no hair or feathers on his body and when he has any cover on his skin at all it takes the shape of scales. A fish is a water back boned animal. A back boned animal is called a vertebrate. A fish is therefore a water vertebrate.

There were fishes before there were any other kind of vertebrates. They have been on the earth longer than birds or beasts or reptiles. They came first, and we have good reason to believe that the fishes are the ancestors of all the others.

But when the forefathers of the land animals found means of keeping alive on the land, so many new opportunities opened out to them and they found so much variety in their surroundings, that they throve and spread amazingly. And there came to be many kinds of them, of many forms, while the rest of the tribe kept in the water and stayed fishes.

And there was always a host of these, and nearly all of them had fishes for their food. So they fought for food and fought for place. Those who could swim fastest got away from the rest, and those who could move quickest got the most to eat. Those with the longest teeth were present at the most meals, and those with the biggest mouths dined with them. And some escaped because they had hard, bony scales, too tough to crack. Some were covered over with thorns, and some had spines in their fins, which they set erect when their enemies would swallow them. And some had poison in their spines and benumbed their enemies, and some gave them electric shocks. Some hid in crevices of rock, or bored holes in the mud, and lay there with their noses and their beady eyes peeping out.