Cornell Nature-Study Leaflets / Being a selection, with revision, from the teachers' leaflets, home nature-study lessons, junior naturalist monthlies and other publications from the College of Agriculture, Cornell University, Ithaca, N.Y., 1896-1904

by New York State College of Agriculture

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.

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.

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.