A TEXT-BOOK OF ZOOLOGY 



CHAPTER I 



INTRODUCTION 



1. Nature presents to man, as he looks upon it, a great and 

 interesting variety of material objects. Each member of the 

 race gathers in his lifetime, by means of experience and infer- 

 ence, a certain limited knowledge of these objects and of the 

 changes which they undergo. The knowledge, thus collected 

 and systematized in the course of the history of the human 

 race, constitutes the so-called Natural Sciences. Every one 

 of us, whether he deliberately chooses or not, must be in some 

 degree a natural scientist. The beauty and interest of the 

 work has attracted and charmed thousands of people of all 

 conditions, in all parts of the world. 



We commonly speak of material objects as either living or 

 non-living — as organic and inorganic. The study of living 

 things in all their relations we call Biology. Physics and Chem- 

 istry are often considered as dealing exclusively with inor- 

 ganic matter, and are therefore placed in contrast with Biology. 

 Their principles apply, however, in the realm of living things 

 just as truly as in the non-living, and one must not imagine 

 because of this antithesis that the phenomena of life can be 

 explained apart from chemical and physical laws. The term 

 Biology was first introduced about the beginning of the nine- 

 teenth century, and is intended to express the fact that plants 

 and animals are similar in their most essential structure and 

 activities. The term Natural History is sometimes used 

 synonymous with Biology. 



2. Zoology. — Owing to the fundamental likeness of all 

 living matter, there is great theoretical difficulty in distinguish- 

 ing between the plant and animal kingdoms. The practical 



