ANIMAL LIFE. 3 



Animals are distinguished from vegetables by the 

 faculty of locomotion, and, in general, by the posses- 

 sion of senses. 



The existence and activity of these distinguishing 

 faculties depend on certain instruments which are 

 never found in vegetables. Comparative anatomy 

 shews, 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, essen- 

 tially 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 nervous apparatus. The phenomena of motion 

 in vegetables, the circulation of the sap, for example, 

 observed in many of the characeae, and the closing of 

 flowers and leaves, depend on physical and mechani- 

 cal causes. A plant is destitute of nerves. Heat 

 and light are the remote causes of motion in 

 vegetables; but in animals we recognize 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 depen- 

 dant on certain external influences which produce 

 motion, the developement of the animal organism 

 is, to a certain extent, independent of these external 



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