ESSAY ON CLASSIFICATION. 



CHAPTER FIRST. 



THE FUNDAMENTAL RELATIONS OF ANIMALS TO ONE ANO- 

 THER AND TO THE WORLD IN WHICH THEY LIVE, AS THE 

 BASIS OF THE NATURAL SYSTEM OF ANIMALS. 



SECT. I. 



THE LEADING FEATURES OF A NATURAL ZOOLOGICAL SYSTEM ARE 



ALL FOUNDED IN NATURE. 



MODERN classifications of animals and plants are based 

 upon the peculiarities of their structure ; and this is gene- 

 rally considered as the most important, if not the only 

 safe guide in our attempts to determine the natural rela- 

 tions which exist between animals. This view of the sub- 

 ject seems to me, however, to circumscribe the foundation 

 of a natural system of Zoology and Botany within too 

 narrow limits, to exclude from our consideration some of 

 the most striking characteristics of the two organic king- 

 doms of nature, and to leave it doubtful how far the 

 arrangement thus obtained is founded in reality, and how 

 far it is merely the expression of our estimate of these 

 structural differences. It has appeared to me appropriate, 

 therefore, to present here a short exposition of the leading 

 features of the animal kingdom, as an introduction to the 

 study of Natural History in general and of Embryology 



B 



