10 PHILOSOPHY OF ZOOLOGY. 



The horse, the sheep, and the cow, though all feeding in 

 the same field, and consuming the same herbage, select 

 different particles from the same mass, and appropriate 

 these to the production of their peculiar organs. 



Even the different members of which an organized body 

 consists, possess this power. From the same circulating 

 fluid, bone, muscle, cartilage, and fat are produced by the se- 

 lective agency of the particular organs. In consequence 

 of this power, each species, and the separate parts of each 

 species, have an individuality of composition by which 

 they are characterized. Thus, within the bark of the 

 oak, we confidently expect to find wood of a more ob- 

 viously fibrous structure, and of greater strength, than 

 underneath the bark of the birch-tree : and the flesh of 

 the sheep has always a different flavour from that of an ox 

 or a horse. Even the particles which are secreted from 

 organized bodies, differ according to the species. Thus 

 we find the perfume of the rose different from that of the 

 thyme, and the smell of the herring, from that of the 

 smelt. 



E. Duration. The same power which we are now con- 

 sidering, is restricted in its action to a determinate dura- 

 tion. It collects the different particles suited to the com- 

 position of the individual, with unceasing industry, ar- 

 rahges them with amazing regularity, and, in spite of nu- 

 merous obstacles, reaches the measure of the standard by 

 which it is regulated. For a time it appears stationary, as 

 to size, structure, and composition. By degrees, however, 

 the functions of this power are exercised with less energy ; 

 the fluids decrease in quantity, and the solids become more 

 rigid; the prelude to the total cessation of all its influ- 

 ence over the inorganic matter with which it is surrounded, 

 and the very organs which it has constructed. 



