“When they are about four weeks old, their feathery gills go away; but, before this, four gill-slits are formed in each side of the tadpole’s head.” Uncle George took a glass tube about twelve inches long, and placing his thumb tightly on one end of it, he pushed it down into the water until the other end was right above a tadpole. Then he took his thumb off, and the tadpole and some water shot up the tube. He then replaced his thumb tightly on the end of the tube, and lifted it out of the water. The tadpole and water remained in the tube as long as he kept his thumb on the end of it. He emptied the contents of the tube into a little dish, and Frank looked at the tadpole with a glass. “I can’t see the gill-slits,” said Frank. “Oh yes, you can, if you look closely. What seems to be a big head is really head and body covered over by a cloak of skin.” “Yes, I see the gills now,” said Frank. “They are red in colour. I also see the cloak. There is an opening on the left side of it.” “That is so,” said his uncle. “That opening is there to let the water into the gills.” At the end of the fifth week, Uncle George took some tadpoles out for the boys to look at. “Do you see any change?” he asked. “Yes,” said Tom, “they have two things like hind legs growing out.” “These _are_ legs,” his uncle said, “and in two weeks from now these legs will have movable joints in them.” Day by day the tadpoles were carefully watched, and the following wonderful changes were observed. When about seven weeks old, their hind legs became jointed, and long toes were formed. The tadpoles were now able to kick out and swim by means of their long hind legs. Their gills went away, and they came to the surface and took mouthfuls of air. They now had lungs instead of gills. But the most striking change came at the end of the eleventh week. One by one they lost the cloak which covered head and body. Under this cloak a pair of fore legs had been folded up and hidden for some time. They were now tiny, wide-mouthed frogs, with long, clumsy tails. The clumsy tails grew smaller and smaller daily. At last there was no tail left, and what was at one time a cluster of black, wriggling tadpoles, was now a crowd of lively little dark yellow frogs. The boys wished to keep them longer, but their uncle told them that they could not do this. “Your tadpoles are now frogs,” he said. “The frog is an insect eater. As we cannot give these little frogs their natural food, we must place them where they can get it for themselves, or they will die.” So the frogs were carried back to their native pond. Exercises on Lesson IX. 1. What are tadpoles? 2. How old is the frog before his hind legs appear? 3. A tadpole seems to be all head and tail. Can you explain this? 4. How do tadpoles breathe—(1) when they are first hatched? (2) when they are four weeks old? (3) when they are eleven weeks old?