Learning with Illustrations An illustration of an organism shows that organism from a particular view or orientation. You might also check for symmetry. Look at the illustration on the following page. A shark has bilateral symmetry. This means that drawing an imaginary line through the center of the animal from the anterior to posterior end forms two mirror images.
Radial symmetry is the arrangement of similar parts around a central point.
An object or organism such as a hydra can be divided anywhere through the center into similar parts. Some organisms and objects cannot be divided into two similar parts. If an organism or object cannot be divided, it is asymmetrical. Regardless of how you try to divide a natural sponge, you cannot divide it into two parts that look alike. Some illustrations enable you to see the inside of an organism or object.