VII THE STUDY OF ZOOLOGY 199 



divisible into three great but subordinate sciences, 

 morphology, physiology, and distribution, each of 

 which may, to a very great extent, be studied in- 

 dependently of the other. 



Zoological morphology is the doctrine of animal 

 form or structure. Anatomy is one of its branches ; 

 development is another ; while classification is the 

 expression of the relations which different animals 

 bear to one another, in respect of their anatomy 

 and their development. 



Zoological distribution is the study of animals in 

 relation to the terrestrial conditions which obtain 

 now, or have obtained at any previous epoch of 

 the earth's history. 



Zoological physiology, lastly, is the doctrine of 

 the functions or actions of animals. It regards 

 animal bodies as machines impelled by certain 

 forces, and performing an amount of work which 

 can be expressed in terms of the ordinary forces of 

 nature. The final object of physiology is to 

 deduce the facts of morphology, on the one hand, 

 and those of distribution on the other, from the 

 laws of the molecular forces of matter. 



Such is the scope of zoology. But if I were to 

 content myself with the enunciation of these dry 

 definitions, I should ill exemplify that method of 

 teaching this branch of physical science, which it is 

 my chief business to-night to recommend. Let us 

 turn away then from abstract definitions. Let us 

 take some concrete living thing, some animal, tho 



