Susan Carter, age 11, of Santaquin, Utah, for her question:
Does a frog hold. his breath under water?‑
The frog is an amphibian, a land and water dweller. His kinfolk include
the toads and salamanders. Some 350 million years ago the first backboned animal left the sea to live on the dry land. This .fellow was an amphibian. Mother Nature smiled on this great victory. She rewarded the amphibians with certain gifts which they have to this day, One of these gifts is a special skin which can absorb or breathe oxygen from the water. So, when you see a frog squatting under the water for ten or twenty minutes, he is not holding his breath. He is breathing through his skin.
All amphibians begin life as fish, during which time they breathe oxygen from the water through fishy gills. Certain salamanders keep their gills and remain fish all their lives. Some give up their gills but do not grow lungs. These fellows breathe through their skin, especially through the skin lining of the mouth and throat. Most amphibians trade their baby gills for adult lungs.
Frogs are among this last group. The teen‑age frog has a pair of lungs for breathing air. He can live on the dry land. He also has the wonderful skin of the amphibian which can absorb free oxygen from the water. This, of course, is a gift he inherited from his brave, remote ancestor, a fellow who left his footprints in the mud of the young Appalachian mountains.
The amphibian skin contains tiny glands which give off a shiny substance called mucus. This mucus evaporates in the air, and this evaporation makes the skin cooler than the air around the amphibian. When you pick up a frog or toad who has been sitting in the air his skin feels cool and dry. In this condition the amphibian is breathing air through his lungs.
The frog or toad cannot absorb moisture through his skin from damp and humid air, but he can from the damp ground and the dewy grass. Toads, who do not return to the water as adults, get all their drinking water by this process. Frogs absorb their drinking water through the skin when they return to the pond. Amphibians never take a drink of water through the mouth as we do.
When a frog is under water the little glands in his skin cover him with slimy mucus and it does not evaporate as it does in the air. It works to capture free oxygen in the water, dissolve it and take it directly into the frog's bloodstream. Meantime, the marvelous skin of the amphibian is taking in all the drinking water the little frog needs.