creamy white fur of the polar bear is especially dense and each of the individual hairs is hollow and contain insulating air spaces. This heavy fur and a large fat layer helps to retain body heat even while the animal is swimming in the coldest arctic weather. The fur does not absorb water so once the animal has climbed out of the water it merely has to shake itself dry. It has plantigrade feet (heel and sole touching the ground), with five sharp claws for gripping the ice. Long hair between the pads protects the bear's feet from the cold and provides traction on the ice.Another adaption is in the thickness of the sub-cutaneous fat. Animals living in cold climates, polar bears and seals for example have a particularly thick layer of sub-cutaneous fat. In the seal and other marine mammals such as whales, the fat is called blubber.In all Endotherms, including polar bears, thermoregulation is controlled by the tuber cinereum of the hypothalamus. If this small downward projection at the base of the brain were to be removed the animal would lose the ability to regulate its temperature and essentially becomes 'cold blooded.'The tuber cinereum is stimulated either by nerve impulses from the cold receptors in the skin or by direct cooling. It is sensitive and will react to temperature changes of only a few tenths of a degree. If the body temperature is too cold, the thermoregulator stimulates a thyroid secretion, which increases the rate of metabolism. If the body temperature continues to drop, the work of internal organs like the liver may be increased and muscle activity in the form of shivering may begin, for muscular activity is the main source of heat available to animals. Camels (Camelus)Camels are large native animals in the desert regions of Asia and northern Africa. There are two types; the Dromedary with one hump and the Bacterian camel that has two humps. The humps are stores of flesh and fat that are absorbed as nutrition when food ...
