GENERAL PURPOSES OP 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 ( 128137), 

 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 



