PKEFACE. 



Experience in teacMng has made me feel how useful a philosophical 

 zoology would be at the present time. By this I mean a body of 

 rules and principles, relative to the study of animals, and applicable 

 even to the other divisions of the natural sciences ; for our know- 

 ledge of zoological facts has made considerable progress during the 

 last thirty years. 



I have in consequence endeavoured to sketch such a philosophy 

 for use in my lessons, and to help me in teaching my pupils ; nor had 

 I any other aim in view. But in order to fix the principles and 

 establish rules for guidance in stud}'^, I found myself compelled to 

 consider the organisation of the various known animals, to pay attention 

 to the singular differences which it presents in those of eaph family, 

 each order, and especially each class ; to compare the faculties which 

 these animals derive according to its degree of complexity in each 

 race, and finally to investigate the most general phenomena presented 

 in the principal cases. I was therefore led to embark upon successive 

 inquiries of the greatest interest to science, and to examine the most 

 difficult of zoological questions. 



How, indeed, could I understand that singular degradation which 

 is found in the organisation of animals as we pass along the series 

 of them from the most perfect to the most imperfect, without en 

 quiring as to the bearings of so positive and so remarkable a fact, 

 founded upon the most convincing proofs ? How could I avoid 

 the conclusion that nature had successively produced the different 

 bodies endowed with Ufe, from the simplest worm upwards ? For 

 in ascending the animal scale, starting from the most imperfect animals, 

 organisation gradually increases in complexity in an extremely remark- 

 able manner. 



I was greatly strengthened in this beUef, moreover, when I recognised 

 that in the simplest of all organisations there were no special organs 

 whatever, and that the body had no special faculty but only those 

 which are the property of all living things. As nature successively 



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