2 PHILOSOPHY OF ZOOLOGY. 



ployed, and many rules have been prescribed, to regulate 

 the principles of zoological nomenclature. 



In order to enter more fully into these important sub- 

 jects, we shall distribute the present volume into Four 

 Parts. In the first, we shall consider the Condition of 

 Animals in reference to their Duration, Distribution, and 

 Economical Uses. In the second, we shall treat of the 

 Methods of Investigation employed to ascertain their struc- 

 ture and actions. In the third, we shall examine the Rules 

 of Nomenclature ; while the fourth will embrace a Gene- 

 ral View of the Classification of the Objects of the Ani- 

 mal Kingdom. 



PART FIRST, 

 ON THE CONDITION OF ANIMALS. 



CHAP. I. 



ON THE DURATION OF ANIMALS. 



JliiACH species of Animal is destined, in the absence of 

 disease and accidents, to enjoy existence during a particu- 

 lar period. In no species, however, is this term absolutely 

 limited, as we find some individuals outliving others, by a 

 considerable fraction of their whole life. In order to find 

 the ordinary duration of life of any species, therefore, we 



