AN INTRODUCTION TO ZOOLOGY 

 FOR MEDICAL STUDENTS 



CHAPTER I 



INTRODUCTION 



THE many things that we encounter in our everyday life 

 we soon learn to divide into two more or less sharply contrasted 

 groups, the living and the non-living. This classification is a 

 fundamental one, and when we come to the Sciences, that is, the 

 ordered and intensive study of these things with a view to under- 

 standing them and explaining them, we find that they also fall 

 into two corresponding fairly distinct categories, the Physical 

 Sciences, treating of non-living things, and the Biological Sciences, 

 concerned with living things. The two groups differ not only in 

 their content, but, as the nature of this is dissimilar, the methods 

 in which they can be investigated, that is to say, the technique, is 

 also different in the two cases. 



Biology is the branch of science that treats of living things in 

 their manifold relations with one another and with non-living things. 

 Living beings are generally recognised as being divided into Plants 

 and Animals, and while, as a matter of fact, we find a certain 

 amount of overlapping between the two when we study them in 

 detail, this is a moderately clear cut division, to correspond with 

 which Biology may be subdivided into Botany, the study of plants, 

 and Zoology, the study of animals. The present book is concerned 

 with the latter, namely Zoology, or more accurately with some 

 aspects of it as illustrated by certain type forms treated in an 

 elementary manner. 



The field covered by Zoology is so vast that it is necessary to 

 split it up into a number of daughter sciences. These fall under 

 two fairly general headings, according to the point of view adopted 

 in making our study. In the first place, we may be concerned 

 chiefly with the questions of the structure of animals, this is termed 

 Morphology, and in the second we may consider in the main the 

 various activities manifested by animals, and this is Physiology. 

 The two require different techniques, but, for the satisfactory 



i B 



