Some of the most interesting adaptations in the animal world are invisible. They are internal adaptations that have helped different animals survive in amazing and unseen ways.

pt. 1. Internal Adaptations: Snakes Had Legs! -- pt. 2. Internal Adaptations: Clownfish Change Genders! -- pt. 3. Internal Adaptations: Male Seahorses Have Babies! -- pt. 4. Internal Adaptations: Female Cheetahs Cheat!.