GENERAL PURPOSES OF NERVOUS SYSTEM. 347 
fabric of organized structure, the highest purpose of the 
Organic Life of Animals is to construct, and to maintain in a 
state fit for use, the mechanism which is to serve as the 
instrument of their Functions of Animal Life ,—enabling them 
to receive sensations, and to execute spontaneous movements, 
in accordance with their instincts, emotions, or will. 
427. This mechanism consists of two kinds of structure,— 
the Nervous and Muscular,—which have entirely different 
offices to perform. The Nervous system is that which is the 
actual instrument of the Mind. Through its means, the indi¬ 
vidual becomes conscious of what is passing around him ; its 
operations are connected, in a manner we are totally unable to 
explain, with all his thoughts, feelings, desires, reasonings, 
and determinations ; and it communicates the influence of 
these to his muscles, exciting them to the operations which 
he determines to execute. But of itself it cannot produce 
any movement, or give rise to any action; any more than 
the expansive force of steam could set a mill in motion, 
without the machinery of the Steam-engine for it to act upon. 
The Muscular System is the apparatus by which the move¬ 
ments of the body are immediately accomplished; and these 
it effects by the peculiar power it possesses of contracting 
upon the application of certain stimuli , of which Nervous 
agency is the most powerful. 
428. Although the presence of a Nervous System is the 
most distinguishing attribute of Animals, yet we do not en¬ 
counter it by any means universally. For among certain of 
those classes which possess on other grounds a title to be 
ranked in the Animal kingdom, it seems beyond a doubt that 
no nervous system exists; and there are many others in 
which, if it be present at all, its condition is so rudimentary, 
that it can take little share in directing the general operations 
of the organism. The life of such beings, in fact, is chiefly 
vegetative in its nature; their movements are not dissimilar in 
kind to those that we witness in Plants; and their title to a 
place in the Animal kingdom chiefly rests upon the nature of 
their food, and the mode in which they appropriated (§§ 7, 8). 
This is the case with the Protozoa generally (§§ 128—137), 
and in a less degree with Zoophytes (§§ 121—127). 
429. In proportion as we ascend the Animal series, how¬ 
ever, we find the Nervous System presenting a greater and 
