395 



the ordinary rule which prevails amongst animals, and con- 

 form to that of vegetables. 



2. These more external differences all depend upon one 

 circumstance, viz., that amongst animals, each individual 

 possesses but one seat of independent vitality, and is hence 

 incapable of being divided into parts, each of which shall 

 continue to live and grow; but in an individual plant, the 

 centres of vitality are greatly multiplied and constantly 

 multiplying. Those animals, however, which resemble 

 plants in the particulars above mentioned, resemble them 

 likewise in containing numerous centres of vitality in a 

 single individual. 



Animals differ from plants in many peculiarities of struc- 

 ture and composition, 



3. The tissues of animals differ in their chemical com- 

 position from those of plants, in containing a considerable 

 proportion of nitrogen, in addition to the oxygen, hydrogen, 

 and carbon of the latter. The principles stored up in the 

 tissues of plants may have nitrogen as an essential consti- 

 tuent ; but not the tissues themselves. But this very general 

 distinction is not universal. The vegetable Fungi contain 

 nitrogen, and some of them have the odour of animal flesh ; 

 on the other hand, the animal tissue of the Frustulia salina, 

 a zoophyte, is proved, by careful analysis by Schmidt, to 

 resemble a vegetable in the absence of nitrogen ; and the 

 same is true with regard to the Cynthia mammillaris, a 

 species of Ascidia, and, probably, with regard to many other 

 animated forms. 



4. The physical structure of animal tissues presents the 

 varieties of form observed in microscopical examination of 

 cellular, muscular, nervous, and the other tissues, of which 

 the entire body of an animal is made up. The tissues of 

 plants present an entirely different microscopical appearance, 

 and much more simplicity of structure, being merely modi- 



