3 8 ELEMENTARY ZOOLOGY 



OTHER MAMMALS 



The mammals constitute the highest group of animals, 

 including man, the monkeys and apes, the quadrupeds, 

 the bird-like bats and fish-like seals and whales; in all 

 about 2500 species. They are found everywhere except 

 on a few small South Sea islands. Only a few species, 

 however, have a world-wide distribution. The name 

 Mammalia is derived from the mammary or milk glands 

 with which the females are provided and by the secretion 

 of which the young of this class, born free in all but a 

 few of the lowest forms, are nourished for some time after 

 birth. In size mammals range from the tiny pigmy-shrew 

 and harvest mouse, which can climb a stem of wheat, to 

 the great sulphur-bottom whale of the Pacific Ocean, which 

 attains a length of a hundred feet and a weight of many 

 tons. Mammals differ from fishes and batrachians and 

 agree with reptiles and birds in never having external 

 gills ; they differ from reptiles and agree with birds in being 

 warm-blooded and in having a heart with two distinct 

 ventricles and a complete double circulation ; finally, they 

 differ from both reptiles and birds in having the skin more 

 or less clothed with hair, the lungs freely suspended in a 

 thoracic cavity separated from the abdominal by a mus- 

 cular partition, the diaphragm, and in the possession by 

 the females of mammary glands. In economic uses to 

 man mammals are the most important of all animals. 

 They furnish the greater portion of the animal food of many 

 human races, likewise a large amount of their clothing. 

 Horses, asses, oxen, camels, reindeer, elephants, and 

 llamas are beasts of burden and draught; swine, sheep, 

 cattle, and goats furnish flesh, and the two latter milk for 

 food ; the wool of sheep, the furs of the carnivores, and 

 the leather of cattle, horses, and others are used for cloth- 

 ing, while the bones and horns of various mammals serve 

 various purposes. 



