128 ON ZOOLOGY. 



consist of a consciousness of a change taking 

 place in any particular part, from a contact of a 

 foreign body with the extremities of the nerves: 

 hence the seat of sensation is in the pulp of the 

 nerves, and the brain, with which the nerves 

 communicate, is the source of perception. Ani- 

 mals, therefore, to possess those attributes, must 

 have a brain and nervous system. And such we 

 find to be directly the case in all red blooded or 

 more perfect animals ; and, indirectly, presumed 

 to exist in the other classes, and even in those 

 where sensation only appears to be present, as in 

 several of the lower orders of worms. 



By the combined operation of perception and 

 sensation, we find most animals endued with 

 very wonderful properties ; and acquire a versa- 

 tility of movements which confer a peculiar inte- 

 rest on their species. Thus from the excitement 

 of their optical organs, by the agency of that 

 transparent matter named light, vision is pro- 

 duced ; by which, with electric rapidity, they 

 notice the objects which surround them, and by 

 repetition, impress upon their memories the re- 

 semblance of each object, so as to discriminate it 

 when again presented to their sight ; and through 

 the same agency, they can more or less compre- 

 hend the motives or feelings by which other living 

 substances are influenced, and avoid or approach 

 them as suits their convenience. By the action 

 or vibration of the atmosphere upon another nerve. 





