As he grew, his skin and shield became too small for him. "This is most uncomfortable," he thought. Split! Skin and shield dropped off. New ones had been growing underneath, but these at first were soft, and he had to shelter under seaweed till they hardened. To his great comfort they were soon firmer than the old ones. Several times he moulted in this way, and each time the new skin and shield came harder and stronger, making him safer from his enemies.
One day a strange thing happened. He lost his appetite. "Whatever is the matter with me?" he wondered. He soon discovered. He was changing his shape. Another eye grew, and three more pairs of legs, and a shield on the front as well as the back.
"Well, I am a fine, strong fellow now," he thought. "I feel as if I could do wonders."
He swam on faster than ever. Indeed, his activity was marvellous. He seemed to shoot through the water. But, strangely enough, he still could not eat, so it is no wonder that at last he grew tired.
"I think I must settle down on something," he said. "This life is really most exhausting. And yet I don't want to sit down on a rock and stay in one place all my life. I wish I could find something moving."
Something moving came through the water, something so huge that to the tiny Barnacle its side was like the side of a world. It was a whale, but Bobby was not afraid. As it slowly lifted its great body through the waves he made his way to it and clung on with all his strength. The whale plunged on his mighty way to colder seas, bearing his little unfelt rider with him.
"Hurrah!" said Bobby. "Now I shall still travel on, without being obliged to do my own swimming."
A more wonderful change than ever before came over him. A tiny bag of cement opened from his head and glued him to the whale's skin. Six strong shells grew round him in an acorn ring, exactly like those of his mother's shell-house on the rock. Four more grew into a door. When he opened the door he could shoot out his twelve curled legs and kick his food down into his mouth in the shell-house. So there he was, living head down and toes up on the whale, and glued so tightly that he could never fall off.
He was grown-up now. All his changes were over. His appetite came back, and he went travelling easily and comfortably with the whale. For all you or I know to the contrary, his roving life may be still going on.