Classifying by Structure

            You are different from other people in important ways. But you are alike in important ways. You have a heart, lungs, a skeleton, and so on. You are made of the same kind of parts as other people, and the parts do the same kind of work. You have the same structure as other human beings.
            Scientists classify by structure. They classify living things into groups according to the kind of parts they have and how they are put together. The structure of a bird is different from that of a butterfly. The structure of an eel is different form the structure of a worm.

How Scientists Classify

            Any system of classification has many "in-betweens." Yet there are good reasons for having a system.
            About 200 years ago, Carolus Linnaeus, a Swedish biologist, developed both a system of classifying and a plan for naming plants and animals. He used Latin names because this language was known to scientists in all countries. He gave each plant or animal two names. One is like your last name; the other is like your first name. For example, one animal is Felis catus, the household cat. Felis concolor is a panther; and Felis leo is a lion. All three of these animals belong to the cat family, but as you can see they are different kinds of cats.