Continually they opened their pink, round mouths to let the water pass through their bodies, in the hope that each fresh mouthful might contain a meal. Again and again, squirt! They were forced to throw out some fragment of shell or rock which had floated in and caused annoyance. At the foot of one pile there was some excitement, for a baby sea-squirt was setting out to see the world. He was impatient to be off, but his mother was giving him a great deal of advice. If you had seen him lying in the water you would never have recognised him as the sea-squirt's son. No mother and son were ever more unlike. She was big, with a thick-skinned tube half a yard long, and a ball at the top shaped like a quince; he was tiny and soft, and looked like a baby tadpole. She was gaily coloured; he was colourless and jelly-like. She was fixed to the jetty pile; he could swim. Yet, in spite of these great differences, mother and son they were. "Dear child," she said, "whatever you do, never stand on your head." "Of course not," he replied; "I shall never wish to." "But you will wish to," cried his mother. "You won't be able to help it. It runs in the family. Listen, son. Once I was like you; I could swim and move about to find my food. Before me, all our grandfathers and grandmothers for millions of years back were for a part of their lives like you. If they had never stood on their heads they might have grown eyes and backbones and fins, and become as great and clever as the fishes. But because those old grandparents became lazy and stood on their heads till they grew to the rocks, we in turn have all grown lazy, and we in turn have been punished by the loss of our swimming powers. If you could only break loose from the family's bad habit, you might start a glorious free race of sea-squirts. All the most successful creatures in the sea are those that have backbones and eyes. You have the beginnings of these two things in you, but if you stand on your head you will lose them, as I have done. You will become fixed and helpless like the seaweeds. Promise me never to stand on your head. Promise me that you will keep moving." "Yes, mother. Oh, yes. Good-bye. Good-bye." The impatient little fellow could wait no longer. "How grown-ups talk!" he thought. "As if I should ever wish to stand on my head!" He swam about for several hours, enjoying himself exceedingly in this great wet world. At last he came to the end pile of the jetty. Here, to his great astonishment, there suddenly came upon him the most overpowering desire to stand on his head. To stand on his head! The very thing his mother had foretold. Well, she was right, after all, so perhaps she was right in advising him to keep moving. "I will swim on," he said.