Probably many more were hatched in the school-house than can be raised in the artificial pond. Return the ones not put in the artificial pond to the natural pond. It would be too bad to throw them out on the ground to die. _Comparing the growth of the tadpoles._--Even when one does his best it is hard to make an artificial pond so good as the natural one for the tadpoles, and the teacher will find it very interesting and stimulating to compare the growth and change in the tadpoles at the school-house with those in the natural pond. As growth depends on the supply of food and the suitability of the environment, it is easy to judge how nearly the artificial pond equals the natural pond for raising tadpoles. It will be worth while to take a tadpole from the natural pond occasionally and put it in with those at the school-house, so that the differences may be more strikingly shown. There is some danger in making a mistake here, however, for there may be three or four kinds of tadpoles in the natural pond. Those of the toad are almost jet black when young, while the others are more or less brownish. If one selects only the very black ones they will probably be toad tadpoles. Every week or oftener, some water plants, and perhaps a small stone covered with the growth of microscopic plants, and some water, should be taken from the pond to the artificial pond. The water will supply the place of that which has evaporated, and the water plants will carry a new supply of food. If the water in the artificial pond in the school-room does not remain clear, it should be carefully dipped out and fresh clear water added. It is better to get the water from the pond where the eggs were laid, although any clear water will answer; but do not use distilled water. The growth and changes in form should be looked for every day. Then it is very interesting to see what the tadpoles do, how they eat, and any signs of breathing. All the changes from an egg to a little toad (Fig. 111), are passed through in one or two months, so that by the first of June the tadpoles will be found to have made great progress. The progress will be not only in size, but in form and action.