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 ave prodiiced 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 herrmg, from that of the 
smelt. 
FE. 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 imdustry, ar- 
ranges them with amazing regularity, and, in spite of nu- 
merous obstacles, reaches the nieasure 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. 
