140 — PHILOSOPHY OF ZOOLOGY. 
are destitute of them,—among Insects, the same species, in 
some genera, can either walk, fly, or swim at pleasure. 
But although the characters furnished by the muscular 
system, are thus various and indefinite with regard to clas- 
ses, they serve to mark the characters of species or genera 
with wonderful precision. 
The three systems of organs which we have considered in 
the three preceding chapters, when viewed in connection, qua- 
lify the animal frame for the higher purposes of existence. 
The insensible parts of the skin, bones, and cellular mem- 
brane, are the rudiments of the singular fabric, and occu- 
py, in reference to their functions, the lowest place in the 
scale. The muscles, though under controul, and occupy- 
ing a subordinate situation, exercise functions of a higher 
kind. ‘The quality of irritability which they possess, per- 
mits them to be excited to action by the application of cer- 
tajn stimulants, and likewise enables the nervous system to 
exercise its absolute controul over them, If all the motions of 
the body be performed by means of the muscles under the 
guidance of the nervous system, we must regard its functions 
as of a still higher kind ; and a closer attention to its vari- 
ous characters, will induce us to assign to it the dominion 
of the body. 'To this system, as to a second class of func- 
tions, we now propose to direct the attention of the reader, 
CHAP. IX, 
ON THE NERVOUS SYSTEM. 
A\s the nervous system contains the organs of sensation and 
volition, and distinguishes animal from vegetable structures, 
it has long occupied the attention of anatomists, and is now 
employed by naturalists as the basis of systematical arrange- 
