The life cycle of a bird or mammal is relatively simple. Once it is born, or hatched, development proceeds directly to an adult form. All along the way, although there are developmental changes, you can easily tell that the animal is a bird or a mammal.<\/p>\n
But for most animals, the life cycle is more complex. An individual makes one or more major transformations during its lifetime; this is called metamorphosis.<\/p>\n
For example, think of a toad tadpole, living in water and eating vegetation, versus an adult toad, living on land and eating insects. Think of a caterpillar, worm-shaped and crawling and chewing vegetation vs. a butterfly, flitting about and sipping nectar. Or a mussel larva, drifting on the sea currents vs. an adult, inside a shell and stuck onto a rock.<\/p>\n