Home › Volumes › Frogs › Toads
American Toad — Part 4
On Monday, the tenth day, we have veritable "pollywogs," as black as tiny coals, with tails that are in a continual wiggle, and small round mouths that are in constant search for something to eat. For the mouths are now open for the first time. These mouths are provided with horny jaws for scraping the tiny plants from their supports and for biting off the delicate ends of larger plants. (The tadpole of Bufo americanus has the following mouth structure: The broad upper lip has two rows of teeth; the broader lower lip has three rows of teeth; the border of the lower lip is fringed with papillae and is doubled in at the corners of the mouth.) The baby toad is not different from other babies in being very hungry when it first comes into the world. He finds the minute green plants just to his taste, and perhaps, too, the microscopically-small animals that are in the ooze of the pond bottom or in the slime at its top, or that cling to water weeds between.
At any time between the middle of June and the middle of July, the shallow water of ponds will be found swarming with toad tadpoles in every stage of development from the fully formed tadpole just described to the perfect little toad. They are exceedingly attractive little creatures. The younger ones may change to toads within the twenty-four hours, so rapid is the development.
The whole length of the tadpole when it is from four to six weeks old and is approaching the last stage of its development is about one inch. The tail with its filmy fin constitutes three-fifths of its entire extent. The soft skin is nearly black, but when we look at it closely--especially with a lens--we can plainly see a fine stippling of gold. The two nostrils are very prominent, showing as small white openings. They eyes are small; the pupil is round and black, and is surrounded by an iridescent iris.
The tadpole now breathes by internal gills (See Leopard Frog, pp. 180; also Bullfrog, pp. 236.) situated at the sides of the throat. The water enters at the nostrils and at the mouth--which is continually opening and shutting for the purpose--passes through openings in the side walls of the throat, thence over the gills, and out through an opening at the left side. (See Leopard Frog, pp. 180; also Bullfrog, pp. 236.) This opening is shaped like a funnel with the small end outermost.
When the tadpole begins to change into the toad, the first sign which we can observe is the appearance of the hind legs. These are mere rounded buds in the beginning and project straight backward. Soon the division into toes can be seen, and the joints are perfected. Then the leg is bent and the foot projects outward. Now the tadpole begins using the legs, as well as the tail, in swimming.
In ten days or two weeks after the appearance of the hind legs, the front ones suddenly appear, fully formed. The fact is they have been growing for quite as long a time as the back legs have, but were concealed under the membrane that covers the gills. When ready for activity, the left one is extended through the breathing-pore, and the right breaks directly through the skin. We now have a strange-looking creature like a little toad with a long tail. For, before the front legs appeared, changes had begun in the region of mouth and eyes. The small mouth has been replaced by a larger one, (See Bullfrog, pp. 236 to 238.) the opening of which extends far back under the eyes. The eyes have increased in size, and have become elevated so that they look like the toad's eyes as we know them in the adult. Now the tail seems mysteriously shorter. It continues to becomes shorter (absorbed from within), until it is a mere stub, and finally disappears altogether. These visible changes with the marvellous and radical transformations that have taken place within, convert our black wiggling "pollywog" into a perfect toad. But so smooth and small! There is no sign of a wart on his brown back and he is smaller than the majority of our tiny tree-frogs at a corresponding stage of development.
For some time before the completion of the metamorphosis, the tadpoles prefer to be wholly or partially out of water. This fact shows that lungs have quite taken the place of the internal gills, and that our little water animals have been converted into land animals. If confined in deep water, tadpoles constantly rush frantically to the top to exchange a bubble of foul air for one of fresh, and they will finally drown if not given opportunity to stay above water.