246 ORGANS OF THE SENSES, 



CHAPTER FIFTH 



ORGANS OF THE SENSES. 



FIRST SECTION. 



General Observations on the Organs of the Senses. 



THE power of locomotion enjoyed by animals, and their 

 mode of nutrition by the conveyance of foreign matter into 

 an internal sac, require them to possess the means of obtain- 

 ing cognizance of the properties of surrounding objects, that 

 they may direct their motions suitably to their ends, and 

 distinguish what is congenial from what is deliterious to 

 their nature. These means of establishing the most intimate 

 relation between external objects and the internal sentient 

 principle, are the organs of the senses, which are instruments 

 placed at the peripheral extremities of certain sensitive 

 nerves, generally those nearest the anterior extremity of the 

 trunk, or around the entrance of the alimentary canal, and 

 which vary in their structure according to the properties of 

 outward matter to which they relate. The organs of the senses 

 are thus necessarily placed in connexion with the external 

 surface of animals, and are not situate upon any of the insen- 

 sitive motor nerves which merely communicate activity to 

 the muscular fibres, nor upon the great ganglionic or sympa- 

 thetic system of unsymmetrical nerves by which the organs 

 of vegetative life throughout every point of the body are 

 kept in incessant activity without our consciousness, but 



