| A | B |
|---|
| backbone | the main bone, made up of many small bones joined together, that runs along the middle of the back in some animals |
| exoskeleton | a hard outer covering that supports 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 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 bya stimulus |
