CHAPTER 1 



Introduction 



1. Zoology and Its Subsciences 



Zoology is one ot the biological sciences, the one dealing with the 

 many different aspects of animal life. Since a "zoo" is a collection of ani- 

 mals, one could easily guess that "zoology" dealt with animals. A visit to 

 a zoo, interesting though it is, can barely begin to suggest the enormous 

 variety of animals that are living today (there are about one million dif- 

 ferent kinds of animals!). In addition to these there are a host of other 

 kinds of animals that have lived in past ages but are now extinct. 



Modern zoology concerns itself with much more than the simple 

 recognition and classification of the many kinds of animals. It includes 

 the study of the structure, function and embryonic development of 

 each part of an animal's body; of the nutrition, health and behavior of 

 animals; of their heredity and evolution; and of their relations to the 

 physical environment and to the plants and other animals of that region. 



At the present time enough facts about animals and their ways are 

 known to fill a whole library of books, and more information appears 

 every year from the intensive researches of zoologists in the field and in 

 the laboratory. No zoologist today can know more than a small fraction 

 of this enormous body of knowledge. Zoology is now much too broad 

 a subject to be treated thoroughly in a single textbook or to be encom- 

 passed by a single scientist. Most zoologists are specialists in some limited 

 phase of the subject— in one of the subdivisions of zoology. The sciences 

 of anatomy, physiology and embryology deal with the structure, func- 

 tion and development, respectively, of an animal. Each of these may be 

 further subdivided according to the kind of animal investigated, e.g., 

 invertebrate physiology, arthropod physiology, insect physiology or com- 

 parative physiology. Parasitology deals with those forms of life that live 

 in or on and at the expense of other organisms. Cytology is concerned 

 with the structure, composition and function of cells and their parts, 

 and histology is the science of the structure, function and composition 

 of tissues. The science of genetics investigates the mode of transmission 

 of characteristics from one generation to the next and is closely related 

 to the science of evolution, which studies the way in which new species 

 of animals arise and how the present kinds of animals are related by 

 descent to previous animals. The study of the classification of organisms, 

 both animals and plants, is called taxonomy. One of the newest biologi- 



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