In a few days all the eggs hatched out, and in place of the little pink eggs there was a crowd of these wriggling creatures and a number of empty egg-skins. The boys were puzzled, and Uncle George had to be consulted. [Illustration: Six Stages in Development of Trout.] “I don’t think these were trout eggs,” said Frank. “The creatures that came out of them are not a bit like fishes. They swim on their sides and have a huge yellow bag attached to their bodies.” “They _are_ young trout, I can assure you, Frank,” said his uncle laughing. “If you remember, your tadpoles were not a bit like frogs when they hatched out of the egg. These huge bags you talk of are called ‘yolks.’ Each trout when hatched is furnished with a huge yolk or food supply. “The tadpole, when hatched, has also got a yolk upon which he lives without eating for four or five days. Our trout will require no food for six weeks. During that time the yolk will become smaller and smaller, and at last disappear entirely. While the yolk is shrinking, you will notice that the creature gradually assumes the form of a fish.” Uncle George emptied the bottle containing the young trout into a wooden box which he had made. This box was fifteen inches long, four inches broad, and four inches deep. The inside of it he had charred with a red-hot iron after it was put together. It was placed under the tap, and the water dripped into it all day and all night. Frank made a small gauze net about the size of a dessert-spoon, and with this they lifted troutlets out of the box whenever they wanted to examine them. As their uncle had said, the creatures changed from day to day. By placing a single trout in a white saucer, the boys could note these changes; but they were such lively little creatures that making good sketches of them was somewhat difficult. First the big black dots became more like eyes. Then delicate fins and tail appeared, and mouths which opened and shut. At the top of the yolk-sac, just under the head, the boys could see a little red thing like a heart beating constantly. As the yolk-sac grew smaller, the little fish’s body grew more shapely, and tiny brown spots appeared all over it. At last, at the end of six weeks, the yolk was completely gone, and the young trout were now beautiful little fish, shaped and coloured exactly like big trout. Then Uncle George began to feed them. They were fed four times a day on the yolk of an egg which had been boiled for half an hour. A very small quantity of this hard yolk was squeezed through a piece of gauze into the water, and the little fishes dashed at it and gobbled it up greedily. They were so rapid in their movements, swimming about and leaping out of the water, that the boys were never tired of watching them. “What are the brown spots on a trout for?” Frank asked his uncle one day.