Upon what does the young tadpole feed?
What is the advantage of external gills at this stage in the tadpole's life?
Later Observations.—The disappearance of the gills, the budding out of the hind legs and, later, the forelegs. While the legs are growing out, the tail gradually becomes smaller, at the same time the shape changes to that of the adult toad with a broad body and large mouth and eyes.
Questions.—What movements has the toad which the tadpole did not have?
What makes these movements possible?
Why is the mouth of the toad better suited to its manner of life than the small mouth of the tadpole would be?
Of what advantage to the tadpole was the smooth outline of its body, and why is the rougher outline of the toad's body better suited for the life of the latter?
Why would gills be unsuitable for the life of the toad?
To the teacher.—From the dark area of the egg the tadpole develops, the dark colour absorbs the sunlight, and this causes growth. The jelly holds the eggs up so that the sun can reach them and it also keeps them from being swept away by the water. The tadpole is very small, and external gills are needed to keep it in very close contact with the water. The tail does not drop off, the substance in it is absorbed into the body of the growing toad to serve as nutriment.
Since all the changes in the development of the toad from egg to adult form take place in about one month, this comparatively rapid development makes the life history of the toad particularly suitable for observation work.