One of these actions should be watched with especial care, for it means a great deal. At first the little tadpoles remain under water all the time, and do not seem to know or care that there is a great world above the water. But as they grow larger and larger, they rush up to the surface once in awhile and then dive down again, as if their lives depended on it. The older they grow the oftener do they come to the surface. This is even more marked in the large tadpole of the bullfrog. What is the meaning of this? Probably most of the pupils can guess correctly; but it took scientific men a long time to find out just why this was done. The real reason is that the tadpole is getting ready to breathe the free air above the water when it turns into a toad and lives on the land. At first the little tadpoles breathe the air dissolved in the water, just as a fish does. This makes it plain why an artificial pond should have a broad surface exposed to the air. If one should use a narrow and deep vessel, like a fruit jar, only a small amount of air could be taken up by the water and the tadpoles would be half suffocated. As the tadpoles grow older they go oftener to the surface to get the air directly from the limitless supply above the water, as they will have to do when they live wholly in the air. _Disappearance of the tail._--From the first to the middle of June the tadpoles should be watched with especial care, for wonderful things are happening. Both the fore and hind legs will appear, if they have not already. The head will change in form and so will the body; the color will become much lighter, and, but for the tail, the tadpole will begin to look something like its mother. If you keep an especially sharp lookout, do you think you will see the tail drop off? No, toad nature is too economical for that. The tail will not drop off, but it will be seen to get shorter and shorter every day; it is not dropping off, but is being carried into the tadpole. The tail is perfect at every stage; it simply disappears. How does this happen? This is another thing that it took scientific men a long time to find out. It is now known that there are two great methods for removing parts of the body no longer needed. In the first method the living particles in the body which are able to wander all around, as if they were inspectors to see that everything is in order, may go to the part to be removed and take it up piece by piece. These living particles are known as white blood corpuscles, wandering cells, phagocytes, leucocytes and several other names. In the other method, the blood and the lymph going to the part to be removed dissolve it particle by particle. Apparently the toad tadpole's tail is dissolved by the blood and lymph rather than being eaten up by the phagocytes, although the phagocytes do a part of the work.