Butterflies, frogs, sharks, and humans all begin life as an egg. So does almost every other animal. The eggs of some creatures — including most mammals — are nurtured inside their mother's body, where they develop into babies that are born alive. But many more animals lay their eggs — either one at a time, by the dozens, or by the millions. Eggs come in a fantastic range of sizes, shapes, and colors. Animals that lay eggs bury them, carry them, guard them, or simply leave them alone. And each egg contains everything needed to create a new living creature.
Houghton Mifflin Harcourt