What is the chief bone in the human body? Does any one say the arm, or leg, or breast-bone? No, it is the backbone, or spinal column. That is a wonderful bone that gives the name of vertebrate or backboned animals to all creatures which possess it. This spinal column, or backbone, is made up of a number of little bones or joints called vertebræ. These are threaded together like beads on a string. The spinal cord runs through them, enters the skull, and expands or blooms out into a brain. Bend your body every way, backward, sidewise, forward, how flexible is this many-jointed spinal column! This wonderful backbone marked the creatures that possessed it as a class higher than the jointed creatures or articulates. [Illustration: THE REIGN OF THE PINE.] We have found that the first vertebrate animals were fishes. The fish of the Devonian age were not only numerous and greedy, but instead of scales the majority of them wore large bony plates, which served them as armor while they fought, not merely for existence, but for conquest. At present there are only about thirty species of plate-wearing or ganoid fish in the world, and nine thousand species without this heavy armor. But in the age when fishes were kings of creation, this proportion was reversed, and the plate-wearing fish were the more numerous. The fishes were the only representatives of the backboned animals until the Coal age was well advanced. Then a new vertebrate of a still higher type arrived in the world. These new creatures aped the fish in their backbones, or spinal columns, their thick skins, and their plate armor. But they were of a higher type than the fishes; for they were in possession of legs, toed-feet, and had lungs instead of gills for a breathing apparatus. In the earliest representatives of this higher stage of life, the lungs were an air sac associated with gills, but the next form dropped the gills entirely, and had well-developed lungs. The possession of lungs gave them power to live out of the water, which hitherto had been the home of nearly all living things. The new vertebrates were amphibians, and no doubt the earliest of them found themselves better fitted to live in the water than on the land, as their legs were feeble, and their strong tails served them well in swimming; but like the amphibians of the present, they made themselves at home in any place.