Come with me, then, to some stagnant pool in a country lane, towards the end of March, and there we shall no doubt find a whole company of frogs, croaking to their hearts’ content after their long winter sleep in the mud at the bottom of the pond. They are wide awake now, and are actively employed laying their eggs. Look carefully around the edges of the pond, especially in that part where the wind has driven the scum to the side, and you will doubtless find in some still corner a gluey mass (_e_, Fig. 15), which looks like a lump of jelly with dark specks in it. Take this up carefully, for it is frog spawn; carry it home together with some weeds from the pond; put it in a glass bowl with water; and then from day to day you may study the history of a frog’s life. [Illustration: Fig. 15. Metamorphosis of the Frog. _e_. Eggs. 1. Tadpoles just out of the egg. 2. With outside gills. 3. With gills hidden, and beak-like mouth. 4. Hind legs appearing. 5. All legs grown, but fish-tail remaining. 6. Putting on Frog appearance; tail being absorbed. 7. Young perfect Frog. ] That jelly-like mass is a collection of frog’s eggs. When they were laid, each egg was a small round dark body in a gluey covering, and they all fell to the bottom of the pond, where, by degrees, the water oozing through the envelope swelled each egg, till they clung altogether in a mass, and, rising, floated at the top. Then very soon each round dot lengthened out into a long streak, and in a few days an eyeless head appeared at one end with a soft closed mouth under it, and at the other a tail, with a soft fin round it like the tail of the lancelet; so that by the time you find the spawn, you may, most likely, be able to see the tiny creature wriggling every now and then in its watery bed. This will go on for some time, and a week or two may pass before the moving tadpole breaks through its egg skin, and coming out into the world, fastens on to a piece of weed (1, Fig. 15) by two little suckers behind its mouth. And now that it is out of the egg the interest begins. Look carefully day after day and you will see some branching tufts (2, Fig. 15) growing larger and larger on each side of its head. What are these? We have not seen them in any fish. No! but if you take a young hound-shark out of his leathery egg before his time, you will find that he has outside gills much like these, only he loses them before he comes out into the world, whereas the tadpole keeps them to breathe with a little longer. If you put the tadpole, at this stage, under the microscope, you can see the red blood flowing through these gills to take up air out of the water.