18 FINAL CAUSES. 



pearing on the stage of life with new organs, new 

 faculties, and new conditions of existence, and 

 undergoing metamorphoses as complete as any 

 that have been depicted in the fables of antiquity. 

 The period at length arrives when the animal, 

 having completed its growth, attains the matu- 

 rity of its being, and acquires the full possession 

 of its powers. Every organ in succession has 

 received its entire developement, and has united 

 its energies with those which had been before 

 perfected. Yet, however complete the arrange- 

 ments that have thus been established, it is still 

 necessary, in order to preserve the whole system 

 in a state in which it may be capable of exer- 

 cising the functions of life, that the materials 

 which compose its fabric should undergo a cer- 

 tain slow, but constant renovation ; and the 

 same circle of actions and reactions, which have 

 brought it to its state of perfection, must con- 

 tinue to be repeated, in order that a due propor- 

 tion may be maintained between the consump- 

 tion and the supply of these materials. In the 

 course of a certain time, however, even under 

 the most favourable circumstances, this equili- 

 brium begins to fail : the energies of the system 

 decline : and the processes of nutrition are in- 

 sufficient to repair the waste in the substance of 

 the body. The fluids are dissipated faster than 

 they can be renewed ; the channels through 

 which they circulate are more and more ob- 



