Life Cycles of Animals 

The life cycle of an organism refers to the sequence of developmental stages that it passes through on its way to adulthood. Mammals, reptiles, amphibians, birds, fish, insects and other invertebrates--they each have their own unique way of reproducing life. There is an amazing variety of life cycles within the animal world. Surprisingly, only about 3% of all animal species give birth to live young as part of their life cycle. Most animals lay eggs.