38 THE FUNCTIONS OF LIFE. 



All forms that perish other forms supply, 



By turns we catch the vital breath and die." — Pope. 



Hence lias the ordinance been issued to a large 

 portion of the animal world that they are to main- 

 tain themselves by preying upon other animals ; 

 either consuming their substance when already 

 dead, or depriving them of life in order to prolong 

 their own. Such is the command given to the 

 countless hosts of living beings which people the 

 vast expanse of ocean ; to the unnumbered tribes 

 of insects which every spot of earth discloses ; to 

 the greater number of the feathered race ; and also 

 to a more restricted order of terrestrial animals. 

 To many has the commission been given to ravage 

 and to slaughter by open violence ; others are 

 taught more insidious, though no less certain arts 

 of destruction ; and some appear to be created 

 chiedy for the purpose of quickly clearing the 

 earth of all decomposing animal or vegetable sub- 

 stances, which might otherwise have filled the air 

 with noxious exhalations, and contaminated the 

 sources of vitality.* 



This new law of animal existence must neces- 

 sarily introduce new conditions of organization and 

 of functions. Structures adapted to rapid locomo- 

 tion must be supplied for the pursuit of prey, and 

 powerful weapons for attack and destruction. But 

 nature has not left the weaker animals unprovided 



* As specially appointed for the performance of this useful office 

 in the police of nature may be cited, among the larger beasts of prey, 

 the hyaena and the jackall ; among birds, the crow and the vul- 

 ture ; among marine animals, the crustacea and numerous mollusca ; 

 and among the lower orders, iimumcrable tribes of insects, such as 

 ants, flesh-flies, &c. 



