Begin with both salamanders in the same aquatic tank. Make observations for a week or two. Move one into the drier tank, while the other stays where it was. Introduce the idea of a control situation. Continue to make observations of both salamanders.
Most amphibians begin life in water and the later change to adapt to life on land.
They replace their gills with nostrils and lungs so that they can breathe the air. They grow legs so that they can get around on land. One individual member of a species does not evolve. Still, it is a good chance for students to observe animal adaptations. It can lead to a deep discussion of natural selection and evolution.