IV. 
OF CLASSIFICATION. 
The Animal Kingdom, a term intended to embrace 
the infinite multitude of living beings that people and 
animate the globe, that fill the air, the earth, and the 
waters with life, is, by the original laws of its organi- 
zation, separated into several distinct divisions. In 
each of these, there prevails a common principle of 
structure, or unity of composition, variously modified 
and complicated, which pervades all the animals con- 
tained within it, and which is independent of, and distinct 
from, that which governs the composition of the others. 
The limits and boundaries of the different divisions have 
not been so thoroughly investigated, as to determine 
the exact relations which obtain among them, or their 
comparative rank according to the perfection of their 
organization and functions. Indeed of many of the lower 
animals very little is yet known ; but, the constant acces- 
sions which are daily made to our knowledge of their 
intimate structure render it certain, that very import- 
ant modifications of the received opinions in regard to 
