4 FUNDAMENTAL PRINCIPLES 



4. Size of Animals. — The smallest animals are invisible without the 

 aid of the microscope and the largest are the 100-foot whales weighing 

 about 150 tons. These huge water animals are probably the largest that 

 have ever existed and far exceed in size the largest terrestrial 63=^-ton 

 elephants. 



5. Distribution of Animals. — Animals are found everywhere on the 

 earth's surface, except perhaps on the glaciated tops of the highest 

 mountains and a very few at the poles. On these mountains creeping and 

 flying forms pass the margins of the snow fields, and the areas of ice and 

 snow at the poles are constantly invaded by such forms as are able to 

 venture into them. Animal life is found throughout the waters of the sea 

 and even penetrates to the deepest parts of the oceans. Animals burrow 

 below the surface of the ground to considerable depths and also follow 

 fissures still deeper to reach the farthest recesses of the most extensive 

 caverns. Finally, myriads of living creatures live within the bodies of 

 other living things, both plant and animal. 



Fig. 1. — Diagram showing the relative size of a small sperm whale, Physeter catodon, 

 of 30 tons and a herd of 24 horses, Equus caballus. The largest whales may be four to five 

 times this size. 



6. Relations of Animals. — Animals are related in various ways to 

 other animals, to plants, and to their physical environment. Between 

 parents and offspring the relation is that of descent. Between other 

 animals the relation may be nutritive, one Uving upon the other; repro- 

 ductive, where two join in the production of young; locomotor, where 

 one attaches itself to another for the purpose of being transported from 

 one place to another; or any one of many other relations which might 

 also be named. Plants serve as food for animals, afford them conceal- 

 ment, and are useful to them in other ways. A sohtary existence, in 

 which one animal fives without any relationship to any other, is possible 

 but rarely occurs in nature. Animals possessing sex associate together 

 for a longer or shorter time as mates. Many of the same kind five 

 together, forming a colony or, as in the case of ants, bees, and wasps, 

 are organized into a society. The relations of animals to their physical 

 environments are manifold. Some are confined to the land, others to 

 the water, and stifi others may be at home in both. Aquatic forms may 

 be restricted to fresh waters, others may be only marine, while there 

 are also those that pass from one to the other environment. Animals 

 exist that spend all of their fives in the soil, and others that enjoy the 

 power of flight pass much of their active existence in the air. 



