A kind of transparent frog achieves near invisibility by hiding its red blood cells during the day, scientists found. "I had never seen anything like that," researcher Carlos Taboada says.

As tiny glass frogs fall asleep for the day, they take almost 90 percent of their red blood cells out of circulation. The colorful cells cram into hideaway pockets inside the frog liver, which ...

This change affords the turtle's body blood that is slightly richer in oxygen than the frog's. Birds and mammals, however, have a fully septated ventricle — a bona fide four-chambered heart.

Glass frogs are mainly found in the rainforests of South and Central America. The species gets its name from its almost transparent skin, which means its heart and other inner organs can be seen.

Water slowly flows back into the cells, blood starts flowing again, and the frog revives. In the lab, Storey said, ice thaws in about 20 minutes and the heart takes another 20 or 30 minutes to start.

Experimental studies have kept frogs in this state for over four weeks, but in Minnesota, Manitoba and Alberta, I am guessing that frogs remain frozen for months. In spring, when the burrow warms and ...