INTRODUCTION 3 



in such a scheme. These two branches are closely allied, and are 

 termed Classification and Taxonomy. 



Physiology, as has been noted, deals with the activities 

 or functions of animals, and falls into three main divisions. The 

 first of these is Ecology or Bionomics, that is to say, the study of 

 the activities and responses of an animal in its natural surroundings., 

 and its relation to other animals, inanimate things, and conditions. 

 This in a way resembles gross morphology, since it requires the 

 use of no special instruments or technical appliances, and as it is 

 not suited to laboratory study is unfortunately omitted from most 

 courses. 



Secondly, we can investigate the activities of an animal or its 

 parts under experimental conditions, testing and measuring them 

 in various ways, and so employing apparatus of a physical nature ; 

 this we usually term Experimental Physiology. A further interesting 

 branch of biology most closely connected with this is Experimental 

 Psychology, which is the study of the responses that an animal is 

 able to make by reason of its possessing a distinct nervous system, 

 and hence in the higher forms often described as a study of the mind. 



Thirdly, the functions of an animal may be approached from 

 the chemical point of view, and their chemical antecedents and 

 results investigated ; this is termed Chemical Physiology, and, as 

 will be seen, requires the apparatus and methods of the chemist. 



A last branch, which although sometimes considered as separate, 

 is nevertheless closely bound up with the first of these, is Distribu- 

 tion. It is obvious, of course, that the reactions of an animal, to a 

 large extent, determine where it is possible for it to live and its 

 activity, whether or not it can spread widely. Distribution itself 

 has two distinct aspects : Geological Distribution, i.e. distribution 

 in time, and Geographical Distribution, i.e. that in space. 



All these various branches of zoology have been concerned 

 with the acquisition and verification by various ways and means of 

 all the many facts relating to animals. Finally, we have left the 

 branch of that science that deals with the correlation of these facts, 

 their reduction to a state of order and arrangement in systems, and 

 further endeavours to ascertain the causes responsible for their 

 production, and to give explanations of the manifold phenomena. 

 This branch, which rounds off the others and borrows extensively 

 from all other sciences, is termed Aetiology, and obviously it is 

 closely concerned with evolution. 



We may divide up the study of Zoology into these various 

 aspects for the sake of clearness in arranging our ideas, but any 

 piece of zoological work cannot be confined to just one of them, it 

 must involve two or three, at any rate, and probably more. 



