vi.] ON THE STUDY OF ZOOLOGY. 83 



employ as the equivalent of botanist, and I shall use the 

 term zoology as denoting the whole doctrine of animal life, 

 in contradistinction to botany, which signifies the whole 

 doctrine of vegetable life. 



Employed in this sense, zoology, like botany, is divisible 

 into three great but subordinate sciences, morphology, 

 physiology, and distribution, each of which may, to a very 

 great extent, be studied independently 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, the commoner the 

 better, and let us see how the application of common sense 

 and common logic to the obvious facts it presents, inevitably 

 leads us into all these branches of zoological science. 



I have before me a lobster. When I examine it, what appears 

 to be the most striking character it presents ? Why, I observe 

 that this part which we call the tail of the lobster, is made up of 

 six distinct hard rings and a seventh terminal piece. If I 



G 2 



