TEXTBOOK OF ZOOLOGY 



CHAPTER 1 

 INTRODUCTION 



An introduction to the science of Zoology may be secured in a 

 variety of ways. One may become interested in the life of field and 

 stream as a hunter and fisherman, or as an amateur naturalist 

 through the collection of specimens. The farmer's son who watches 

 the insects that devour the crops and who protects insect-eating 

 birds may become sometliing of a zoologist unawares. The boy or 

 girl who studies Anatomy and Physiology in school becomes famil- 

 iar with structure and function as found in the bodies of higher 

 animals. A high-school course in Zoology or in Biology offers a 

 more comprehensive introduction. Whatever may have been the 

 student's previous experience with zoological science, it is desirable 

 that he make the most of it throughout the study outlined in the 

 present volume. 



The Biological Sciences. — The term science may be applied to 

 any body of exact knowledge. The Natural Sciences are those 

 dealing with the facts of nature, in contrast with the Social Sciences, 

 which deal Avith the facts of human nature. According to such a 

 classification, the Social Sciences are contrasted with the Natural 

 Sciences, as though the two were distinct. But the human rela- 

 tionships with which the Social Sciences deal are facts of nature 

 no less than the phenomena of Chemistry or Physics. Hence it is 

 better to say that the Social Sciences are conveniently set off, as 

 deahng with human relationships, over agamst all other sciences, 

 which are called the Natural Sciences. These Natural Sciences 

 may be divided into two groups : the Physical Sciences, which are 

 concerned with non-Hving bodies; and the Biological Sciences, 

 which are concerned with organisms, or hving things. Thus Cheni- 



