The document defines the characteristics of mammals, birds, reptiles, amphibians, fish, and insects. Mammals have hair, give birth to live young, and feed their babies milk. Birds lay eggs, have feathers and wings, and can fly. Reptiles lay eggs, have scales, and may have no legs or four legs. Amphibians have wet skin and live both on land and in water. Fish lay eggs, live only in water, have scales, fins, and gills. Insects have six legs, a head, thorax, abdomen, and antennae and are invertebrates that lay eggs.