GENERAL ZOOLOGY. 



The foregoing pages have been largely devoted to the 

 study of the structure of animals and the various degrees of 

 structural resemblances which they bear to each other 

 as expressed by classification. Animals, however, pre- 

 sent other points for consideration, and some of these 

 may be referred to here. 



COMPARATIVE PHYSIOLOGY. 



An animal must be regarded as a mechanism, but our 

 knowledge of a machine is not complete when we know 

 its structure; we must also understand the way the differ- 

 ent parts perform their work. The study of the stiucture 

 of an animal is the province of anatomy, while that branch 

 of science which deals with the action of the various parts 

 and the working of the whole is called physiology. 



It is a far more difficult task to ascertain from the speci- 

 mens themselves the function of the parts and the way 

 that they act, than it is to make out the details of struct- 

 ure, and so a general summary is given here. 



Every machine, in order that it may perform work, 

 must be supplied with energy, and the animal obtains 

 this energy by the slow combustion (oxidation) of food 

 or food products, just as the steam-engine gets its energy 



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