It requires only a short time for the eggs to hatch. In warm weather two to four days are usually sufficient, but in the cool days of April it may require ten days. As the changes are so very rapid, the eggs ought to be carefully looked at two or three times a day to make sure that all the principal changes are seen. If a pocket lens or a reading glass is to be had it will add to the interest, as more of the details can be observed. But good sharp eyes are sufficient if no lens is available. _Hatching._--Watch and see how long it is before the developing embryos commence to move. Note their change in form. As they elongate they move more vigorously till on the second or third day they wriggle out of the jelly surrounding them. This is hatching, and they are now free in the water and can swim about. It is curious to see them hang themselves up on the old egg string or on the edge of the dish (Fig. 112). They do this by means of a peculiar v-shaped organ on their heads. [Illustration: _Fig. 113. Older toad tadpoles with their heads up._] How different the little creatures are, which have just hatched, from the grown up toad which laid the eggs! The difference is about as great as that between a caterpillar and a butterfly. _Tadpoles, polliwogs._--We call the young of the frog, the toad and the tree toad, tadpoles or polliwogs. The toad tadpoles are black. As they increase in size they may become greyish. Those raised in the house are usually darker than those growing in nature. The tadpoles will live for some time in clear water with apparently nothing to eat. This is because in each egg is some food, just as there is a large supply of food within the egg shell to give the chicken a good start in life. But when the food that the mother supplied in the egg is used up, the little tadpoles would die if they could not find some food for themselves. They must grow a great deal before they can turn into toads; and just like children and other young animals, to grow they must have plenty of food. _Feeding the tadpoles._--To feed the tadpoles it is necessary to imitate nature as closely as possible. To do this, a visit to the pond where the eggs were found will give the clue. Many plants are present, and the bottom will be seen to slope gradually from the shore. The food of the tadpole is the minute plant life on the stones, the surface of the mud, or on the outside of the larger plants. One must not attempt to raise too many tadpoles in the artificial pond in the laboratory or school-room or there will not be enough food, and all will be half starved, or some will get the food and the rest will starve to death. While there may be thousands of tadpoles in the natural pond, it will be readily seen that, compared with the amount of water present, there are really rather few.