THEORIES. 163 



hour, but by an appeal to the testimony of every 

 naturalist, from the earliest times to our own. 



It has been judiciously said by Dr. Mantell, a 

 diligent and persevering observer in an extensive 

 field of organic nature, and one of the first philo- 

 sophers who exposed the fallacy of this vaunted 

 theory : 



"Although it is now a received physiological 

 axiom, that cells are the elementary basis, the ulti- 

 mate limit, of all animal and vegetable structures ; 

 and that the varied functions, in which organic life 

 essentially consists, are performed by the agency of 

 cells, which are not distinguishable from each other 

 by any well-marked characters ; there is not any 

 ground for assuming any identity between the 

 primary cells, even of the simplest species of 

 animals or vegetables, much less between those of 

 more complicated organization. The single cell 

 which embodies vitality in the monad, or the yeast 

 fungus, is governed by the same immutable organic 

 laws which preside over the complicated machinery 

 of man, and the other vertebrata ; and the single 

 cell which is the embryotic condition of the mam- 

 mal has no more relation to the single cell which is 

 the permanent condition of the monad, than has the 

 perfect animal into which the mammalian cell be- 

 comes ultimately developed. The cell that forms 

 the germ of each species or organism is endowed 

 with special properties, which can result in nothing 

 but the fabrication of that particular species. The 

 serious error which pervades the theory advanced 



