IX.—TADPOLES. The frog spawn, when first put into the big glass bell, was just a mass of jelly-like stuff studded all over with black dots. When looked at closely, it was seen to consist of many round, clear eggs. Each egg was surrounded by a thin skin, and had, in its centre, a little round black ball or yolk. At the end of a week all these black yolks had lost their round shape. They were now long and oval. During the next four days these oval yolks became little moving animals, each having a head, body, and tail, but no limbs. From the head of each there grew out two pairs of feathery objects. These, Uncle George told the boys, were gills or breathing organs. Soon another pair of these feathery gills appeared: so that each little creature had now three on each side of his head. By the end of the second week the little creatures had all wriggled out of the eggs. They hung together by their feathery gills in little black groups. “What shall we feed them on?” Frank asked his uncle. “They are not at all nice in their tastes,” Uncle George replied. “They will eat almost anything, from water weeds up to drowned kittens. If they get nothing else, they will eat one another, and not mind it a bit.” “How dreadful,” said Frank. “Hadn’t we better give them something to eat now, for fear they may eat each other up.” “It wouldn’t do much good giving them anything to eat now, for they have _no mouths_.” [Illustration: The Development of the Tadpole. 1. Portion of Frog Spawn. 2. Same after ten days. 3. A Newly-Hatched Tadpole. The remaining figures show the same Tadpole at (4) one week; (5) three weeks; (6) seven weeks; (7) eleven weeks; (8) thirteen weeks; and (9) fourteen weeks after hatching.] “No mouths, Uncle George?” “No mouths,” Uncle George repeated. “Is it not curious? For four days the tadpole, or young frog, has no mouth, and yet during that time he grows a great deal. “Four days after he leaves the egg his mouth appears. It is a very small mouth, fringed with frilled, fleshy lips. These lips are moved by a pair of strong, horny jaws. This mouth is very different from the wide, gaping mouth of the frog.” Just as Uncle George had said, the tadpoles ate nothing for four days. Then their mouths appeared, and they began to eat the water weeds. But Uncle George fed them on raw meat. He said it made them grow quickly. A small piece of raw beef, tied to the end of a string, was lowered into the tank, and the tadpoles swarmed around it. What was left of the beef was pulled out every morning, and a fresh piece put in. By this means the water was kept clean, and had only to be changed once a week. “Why, they have no gills now,” said Frank one day, as he was helping his uncle to change the water. “Oh yes, they have, Frank. They have gills like a fish now.