4 RELATIONSHIPS OF THE LIVING WORLD Chap. 1 



mals and man extend in every direction and include all living organisms and 

 the times and places which have made them and are still making them what 

 they are. 



The second way of studying animals is with emphasis on the individual. It 

 is the study of the structure and function of tissues and organs, by examination 

 and experiment. Every animal has an internal environment inherited from its 

 ancestors through ages of evolution. Within the body all cells live in a watery 

 environment as truly as do animals in a pond. The amount of water is con- 

 tinually regulated; chemical conditions — acidity, alkalinity, enzyme, and hor- 

 mone actions are constantly balanced, unbalanced, and rebalanced; physical 

 conditions are changed; temperatures shift, and pressures vary. Every animal 

 body holds a special environment of which there is no duplicate and probably 

 nothing in existence that is at once so complex, delicate, and generally durable. 

 The release of energy in respiration, chemical regulation by the endocrine 

 glands, and the excretion of the by-products of metabolism especially empha- 

 size the balancing associated with these processes. As animals are examined, 

 it becomes more and more clear that there are not thousands of separate facts 

 to be learned, but a few associations and principles that apply to essentially 

 similar things. 



The Fields and Subdivisions of Zoology. The science of biology includes all 

 living organisms. The term, actually meaning the science of life, Gr. bios, and 

 logos, discourse, is used commonly and loosely, often with little understanding 

 of its meaning. It may include only the plants and be called the biology of 

 plants; it often deals only with animals, the biology of animals. In either case 

 it is concerned with the general facts and principles of plant or animal life. 



Zoology is the study of all aspects of animals, including their relations to 

 each other and their environments in time and space. Other associated sciences 

 are those particularly concerned with the environment, such as geology, physi- 

 ography, oceanography, and meteorology which is concerned with conditions 

 of the atmosphere. All of these are supported by physics, treating of the prop- 

 erties of matter, and by chemistry which deals with its constitution. 



There are many subdivisions of zoology, the science of animals (including 

 man). The principal ones are the following: 



Subdivisions of Zoology 

 Name Description 



Anatomy Gross structure of the animal 



Histology Function and microscopic structure of tissues and organs 



Cytology Function and structure of the cell and its contents 



Physiology Function of the whole animal, or of its parts 



Embryology Development of the new individual 



