Page 45 - Reading Success B3

Mammals are vertebrates, which means that they have backbones. They use
lungs to breathe, are warm blooded , and typically have four legs. Other

vertebrates, such as amphibians, birds, and fish, also have some of these
features. However, unlike mammals, these creatures do not have hair that grows

out of their skin at some point in their lives. All female mammals have mammary
glands, which are special glands, which produce milk for their young to feed on.

Most mammals are born alive from the mother’s body instead of from eggs laid
outside of their mother’s body.

Mammals can live in many types of environments: in deep oceans, steamy

jungles, in polar snows, or blazing deserts. They can live in these environments
because they are warm-blooded. No matter what the temperature of their

surroundings is their bodies remain at about the same temperature.

Their hair also helps keep their body temperature at constant level. Every
individual hair is controlled by a tiny muscle in the skin. If it is cold, these muscles

raise the hair to insulate the body. When the weather is hot, the muscles stand the
hair even straighter so that air moves around the hair and cools the body. Some

mammals, like human beings do not have much hair. These mammals have sweat
glands in their skin. These glands secrete a liquid called perspiration. When this

liquid evaporates it cools the skin and keeps the body temperature in its normal
range .

Main Idea

What is the main idea of this story?

a. some features of mammals

b. some specific types of mammals
c. why mammals have hair

d. what mammary glands are used for

48_Reading Success B 3