Polliwog. An interesting word. The word itself comes in a variety of forms, and has changed over time. The word first appeared in Middle English as "polwygle" and comes from words that mean "head" and "to wiggle." And that is what a polliwog is, if you think about it. A little wiggling head, swimming around in streams and ponds, turning into, eventually, a frog. Other forms of the word include pollywog and polliwig. Another word for the same little creature is "tadpole."
Polliwogs are the infant stage in the life of a frog. Frogs are amphibians, which means that they live comfortably on both land and water, or spend their early life in water, and later life mostly on land. It also means that in their infant stage, amphibians are like fish, getting their oxygen through breathing in and processing water. In their adult stage they breath air.
Let's look at the life-cycle of a frog. A frog will begin its life as an egg. When it hatches, it is little more that a swimming (wiggling) head with a mouth, gills and a tail. It is small and faces a precarious existence. Because it is so small and cannot really defend itself, it will hide out among weeds or grasses growing or floating in the water that is its home. As it absorbs what is left of the egg that was its first home, it grows, and begins to swim, looking for algae to eat.
When our polliwog is four weeks old, skin will begin to grow over the gills, and lungs will be developing. Our polliwog will swim around with other polliwogs, and the group will look like a small school of small fish. They are social little creatures.
At the age of six to nine weeks, our polliwog will start to sprout legs, and begin to "absorb" his own tail. His head becomes more distinct, his body gets a little longer, and he develops teeth to enable him to eat dead insects and plants.
When our polliwog reaches the age of 12 weeks, his tail is almost gone, and he looks like a small frog. Which is what he is-sort of a frog equivalent of a "teenager," we can call him a froglet.
Between the age of 12 and 16 weeks, our polliwog has completed his transformation, his metamorphosis, and is an adult frog. He can now go out and meet his "frog princess" and they can start the process all over again, mating and laying eggs to start the next generation of egg to polliwog (tadpole) to froglet to frog.