Now you see them, now you don’t. Some frogs found in South and Central America have the rare ability to turn on and off their nearly transparent appearance, researchers report Thursday in the journal ...

Now you see them, now you don't. Some frogs found in South and Central America have the rare ability to turn on and off their nearly transparent appearance, researchers report Thursday in the journal ...

Glass frog photographed during sleep and while active, showing the differences in red blood cells within the circulatory system. Jesse Delia via AMNH When a tiny glass frog dozes off to sleep, its ...