| A | B |
|---|
| backbone | The main bone, made up of many small bones joined ttogether, that runs along the middle of the back of some animals |
| exoskeleton | A hard outer covering that suppports and protects some animals without backbones |
| molt | To shed an animal's outer covering |
| gills | Organs for breathing found in fish and amphibians |
| amphibian | One of a large group of animals with backbones that live part of their lives in water and part on land |
| reptile | an animal with a backbone that has a dry, scaly skin |
| mammal | An animal with a backbone that usually has hair on its body and feeds milk to its young |
| behavior | The way a living thing acts |
| instinct | A behavior that an animal is born with and does not need to learn |
| reflex | A simple, automatic behavior |
| stimulus | The cause of a behavior |
| response | A behavior caused by a stimulus |
