Mammals
MammalsMammal, common name applied to any warm-blooded animal
belonging to the class that includes humans and all other animals that
nourish their young with milk, that are covered with varying amounts of
hair, and that possess a muscular diaphragm. Mammals have the most
highly developed nervous systems of all animals. Most members of the
group have four appendages, usually legs. These may be adapted for use
as swimming appendages, as in seals, or as wings, as in bats. Some
Types,, however, have two limbs that have been reduced to small
vestiges beneath the skin, as in whales, or have been lost altogether, as
in sea cows. All mammals, except the egg-laying monotremes, produce
live young that undergo the early stages of development within the body
cavity of the mother. Some mammals are helpless at birth, others are
able to walk and even run immediately, and may be born fully furred
and with their eyes and earsopen. The largest mammal, the blue whale,
Often exceeds 30 m (100 ft) in length, and the smallest shrews, mice,
and bats are often less than 5 cm (less than 2 in) in length.
In many mammals the color of the skin or fur blends with the animal�s
natural surroundings. In others there is great contrast with the natural
surroundings to favorvisual signals that provide information about
theidentity of a species, and about the gender, age, orsocial status of an
individual. The skin also functions as a sensory and excretory organ and
contains specialized glands. Mammary glands, which are present in
fully developed form in all adult female mammals.
Aquatic mammals, such as whales, dolphins, and sea cows, have no
sweatglands. Sweat glands are usually located at the base of hairs,
except those in regions of skin bordering mucous membranes, such as
the sweat glands surrounding the edges of the lips and covering the
genitalia. Many mammals, however, have few functional sweat glands;
in dogs and cats, for example, only the glands...
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