Amphibians are vertebrates distinguished by their ability to live in both aquatic and terrestrial habitats. Amphibians include the frogs and toads, salamanders and newts, and caecilians. The name, derived from the Greek amphibios meaning "living a double life," reflects this dual aptitude. Most species live part of their lives underwater and part on land. Most amphibians reproduce by laying soft eggs in masses or long strands. Most females lay eggs in the water, and the offspring live in the water using gills to breathe as fish do. As the offspring grow, most amphibians develop legs and lungs that allow them to move onto land. This big change is called "metamorphosis." Most amphibians have delicate, thin skin that aid in the animal's ability to breathe. An amphibian's thin skin also makes it sensitive to pollution and changes in climate. Amphibians are ectothermic or "cold-blooded", like fish and reptiles. Ectothermic animals cannot regulate body temperature internally. You can visit the Philadelphia Zoo's amphibians in the Reptile and Amphibian House.