TEXTBOOK OF ZOOLOGY 



CHAPTER I 

 INTRODUCTION 



In whichever direction we turn or wherever we go, whether in 

 the air, on land, or in the sea, we are surrounded by living creatures. 

 Their very presence presents problems and fills us with curiosity. 

 We ask questions. From whence do they come? What is the 

 source of their energy? Why are there so many different kinds? 

 What is our relation to other living things? What is life? Such 

 questions and endless numbers of similar ones kindle the interest 

 of every thinking person. The constant endeavor on the part of 

 man to answer these questions and solve the problems of the origin 

 and nature of life has given us the field of study known as biology. 



Biology is a word derived from two Greek words, hios, life, and 

 logos, discourse, and is the name universally applied to the study 

 of living organisms and life processes. Since living things fall 

 largelj^ into tAvo general categories, plants and animals, such a 

 study deals with the forms and phenomena exhibited by both. 



The Biological Point of View 



Nature is ever inviting investigation ; her forces are in constant 

 operation about us, but she hides the truth. The biologist looks 

 upon himself as a seeker after truth, as one striving to get a glimpse 

 into the mysteries of life. As he succeeds in obtaining these 

 glimpses, he soon realizes the existence of certain fundamental 

 features common to the structure and function of all living forms. 

 He soon recognizes the oneness of all life, and himself as a part of 

 one great organic system, each unit of which has some relation to 

 the whole. A biological concept may rest upon observations, which 

 may be changed from day to day by the discovery of new facts, but 

 the biologist, like the chemist or physicist, is justified in holding to 

 a theory or hypothesis as long as it provides a true working basis 

 for further investigation. 



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