4 FUNDAMENTAL PRINCIPLES 



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

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

 mountains and 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. 



5. 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 living 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 solitary existence, in 

 which one animal lives 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 live 

 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 still 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 lives in the soil, and others that enjoy the 

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



6. Definition of Zoology. — A study of animals from every aspect 

 constitutes the science of zoology. This broad field is capable of being 

 divided into many of less extent depending on the various aspects from 

 which animals may be viewed, whether considered in whole or in part, 

 as to structure or function, in relation to the inorganic environment or 

 to other animals and the plants about them, or from the standpoint of 

 the principles and laws which underhe and determine the phenomena 

 exhibited by animal life. 



7. Divisions of the Subject. — Zoology may be divided, in accordance 

 with the manner in which animals are studied, into two great sub- 

 sciences; these are morphology, which deals with animals as to form 

 and structure, and physiology, which deals with them as to their 

 functions. 



