OF THE NERVOUS SYSTEM. 105 



nervous system, and even this seems to be occasionally entirely 

 absent. In speaking of these various groups of animals, the 

 peculiarities here adverted to will be noticed. 

 Let us now consider the functions of the system. 



194. Sensibility is the faculty to receive impressions, 

 and to have a consciousness of 

 them. It belongs to all animals, 

 but in different degrees. As we 

 ascend in the zoological scale, the 

 sensations become more and more 

 varied, the knowledge acquired 

 through them greater, the nervous 

 system more complex. 



195. In the lowest class of 

 animals, the structure is at first 

 very simple, and their sensations 

 do not seem very distinct. In the 

 earth-worm, a knotted cord extends 

 throughout the whole length of 

 the body, and to and from these 

 knots or ganglions the nerves pro- 

 ceed; but each of these parts seems Fig 68 ._ Nervous System of 

 equal to every other, and there is an Insect (Carabus of the 

 no specialization of any. This gardens). A Beetle, 

 simplicity of structure gives way 

 to a form more complex as we ascend in the animal scale. 



196. Functions of the Nerves. All parts of the body 

 are not equally supplied with nerves, and there are parts 

 which seem to have none. Hence, no doubt, is the fact that 

 whilst some parts are extremely sensitive, others are but little 

 so, or wholly insensible. No experiments are required to 

 show that a part owes its sensibility to the contiguity of the 

 nerve which connects it with the central organs of the nervous 

 system. The nerves, then, are not the organs by which the 

 sensations are perceived ; they merely transmit them to the 

 central system, where all perception resides. 5 * 



197. Where, then, is the seat of the faculty of percep- 

 tion ? Which is the perceiving organ ? 



198. Influence of the Encephalon. Does perception 

 reside in the spinal marrow, the cerebellum, or the cerebrum ? 



* It is now certain that perceptions or impressions on the central organs of 

 the nervous system are of two kinds ; one attended with consciousness, the 

 other without. R. K. 



