ANIMAL LIFE. 3 



Animals are distinguished from vegetables by the fac- 

 ulty of locomotion, and, in general, by the possession 

 of senses. 



The existence and activity of these distinguishing 

 faculties depend on certain instruments which are never 

 found in vegetables. Comparative anatomy shows, that 

 the phenomena of motion and sensation depend on 

 certain kinds of apparatus, which have no other relation 

 to each other than this, that they meet in a common 

 centre. The substance of the spinal marrow, the 

 nerves, and the brain, is, in its composition, and in its 

 chemical characters, essentially distinct from that of 

 which cellular substance, membranes, muscles, and skin 

 are composed. 



Every thing in the animal organism, to which the 

 name of motion can be applied, proceeds from the ner- 

 vous apparatus. The phenomena of motion in vegeta- 

 bles, the circulation of the sap, for example, observed 

 in many of the characeae, and the closing of flowers and 

 leaves, depend on physical and mechanical causes. A 

 plant is destitute of nerves. Heat and light are the 

 remote causes of motion in vegetables ; but in animals 

 we recognise in the nervous apparatus a source of 

 power, capable of renewing itself at every moment of 

 their existence. 



While the assimilation of food in vegetables, and the 

 whole process of their formation, are dependent on cer- 

 tain external influences which produce motion, the 

 development of the animal organism is, to a certain 

 extent, independent of these external influences, just 



