50 ZOOLOGICAL PHILOSOPHY 



comparing or combining these ideas, and of forming judgments which 

 are merely ideas of another order ; in short, of thinking. Not only is 

 this the greatest marvel that the power of nature has attained, but it 

 is besides a proof of the lapse of a considerable time ; since nature 

 has done nothing but by slow degrees. 



As compared to the periods which we look upon as great in our 

 ordinary calculations, an enormous time and wide variation in successive 

 conditions must doubtless have been required to enable nature to bring 

 the organisation of animals to that degree of complexity and develop- 

 ment in which we see it at its perfection. If an inspection of the 

 numerous diverse strata composing the external crust of the earth 

 furnishes unimpeachable testimony of its great antiquity ; if the very 

 slow but continuous displacement of the sea-bottom,^ certified by the 

 numerous monuments left everywhere about, gives further confirmation 

 of its prodigious antiquity ; then the belief is justified that the state of 

 perfection at which the organisation of the most perfect animals has 

 arrived, contributes to exhibit that truth in the strongest possible light. 



But in order that this new proof may be securely based, it will first 

 be necessary to bring into evidence the facts concerning the actual 

 progress of organisation ; it will be necessary to verify if possible 

 the reahty of that progress ; finally, it will be necessary to collect 

 the best established facts and to identify nature's methods in bring- 

 ing her productions into existence. 



Meanwhile, let us note that although the term productions of nature 

 is generally accepted for indicating the beings which constitute each 

 kingdom, it seems none the less that no definite idea is attached to that 

 expression. Apparently, prejudices of special origin prevent the 

 recognition of the fact that nature possesses the faculty of herself 

 bringing so many different beings into existence ; of causing incessant 

 though very slow variations in living races ; and of maintaining 

 everywhere the general order that we observe. 



Let us leave aside all opinion whatever on these great subjects ; 

 and to avoid any error of imagination let us everywhere consult 

 nature's own works. 



In order to be able to bring under our attention the totahty of exist- 

 ing animals, and to place these animals under an aspect easily under- 

 stood, we must remember that all the natural productions that we can 

 observe have long been divided by naturalists into three kingdoms, 

 under the name of animal kingdom, vegetable kingdom and mineral 

 kingdom. By this division, the existences comprised in each of these 

 kingdoms are compared together under a common standard ; although 

 some have a very different origin from others. 

 ' Hydrogéologie, p. 41 et seq. 



