Ernestine Levesque, age 11, of Niagara Falls, Ontario, Canada, for her question:

How does a hibernating turtle breathe?

Turtles and tortoises are slow breathers at all times. When they sink into the deep coma of hiberation, they need very little air and breathing slows down almost to a stop. They hibernate to escape the winter cold and estivate to escape the hot droughts of summer. Usually their hideaways are burrows or earthy dens in dirt, sand' or mud. There is not much space to spare, but there are enough air pockets to supply their limited breathing.

These gentle creatures do everything in slow motion. Perhaps this is the secret of their long life spans and also the age old success of their family tree. Their ancestors were here when the first dinosaurs arrived, long before the birds and mammals. Fossil records proved that at least 250 turtles and tortoises became extinct during the past 100 million years. But the 250 surviving species have not changed their shapes or their life styles very much during the past 200 million years.

Tortoises spend much of their time on land and turtles are adapted to life in the water, though all of them must breathe air. They are reptiles classed as chelonians and their basic body plan poses a breathing problem. It has both a bony internal skeleton and an outer shell or armor. The ribs are more or less sealed to the roof of the shell. They cannot help the lungs to expand and contract.

This problem, however, was solved ages ago by chelonian ancestors. Two side muscles enlarge the chest cavity to suck in fresh air and a complex third muscle squeezes them to expel stale air. Even when a chelonian is out and about, his breathing and other body processes go on in slow motion. After a period of feasting, it may take several months to digest his stores of food and water    during which time he fasts.

This talent helps him to solve the serious handicap of being a cold blooded creature, with no built in thermostat. He is busiest and possibly most comfortable at ordinary room temperatures. But he has no way to cope with the cold dry winter or with exposure to the hot, dry sun. Hence, he must hibernate to avoid the cold and estivate to avoid a long spell of hot drought.

Before going into hiding, he usually eats extra food and grows fat. He also drinks extra water to fill his built in storage flasks. He is a born digger and his hiding place is an underground den at the end of a burrow. The air down there may be somewhat stale, but there is enough to supply him during his long rest period.

One of the best diggers is the gopher turtle, who is really a tortoise. He lives in the South where winters are mild and summers are often too hot and dry for his comfort. When time comes to estivate, his long burrow may be shared by frogs and mice, crickets, beetles and various other small tenants. They too need to escape the drought and the turtle's sleeping quarters provide enough air for them all.