48 ESSAY ON CLASSIFICATION. 



If the naturalists of past centuries have failed to im- 

 prove their systems of Zoology by introducing considera- 

 tions derived from the habitat of animals, it is chiefly 

 because they have taken this habitat as the foundation of 

 their primary divisions. But, reduced to its proper limits, 

 the study of the connexion between the structure and the 

 natural home of animals cannot fail to lead to interesting 

 results, among which the growing conviction that these 

 relations are not produced by physical agents, but deter- 

 mined in the plan ordained from the beginning, will not 

 be the least important. 



The unequal limitation of groups of a different value 

 upon the surface of the earth produces the most diversi- 

 fied combinations possible, when we consider the mode of 

 association of different families of animals and plants in 

 different parts of the world. These combinations are so 

 regulated that every natural province has a character of 

 its own, as far as its animals and plants are concerned; 

 and such natural associations of organized beings, extend- 

 ing over a wider or narrower area, are called Faunae, when 

 the animals alone are considered, and Florae, when the 

 plants alone are regarded. Their natural limits are far 

 from being yet ascertained satisfactorily everywhere. As 

 the works of Schow and Schmarda may suffice to give an 

 approximate idea of their extent, 1 I would refer to them 

 for further details, and allude here only to the unequal 

 extent of these different faunae, and to the necessity of 

 limiting them in different ways, according to the point of 

 view under which they are considered ; or rather show, 

 that, as different groups have a wider or more limited 



1 I would also refer to a sketch I (Philadelphia, 1854, 4to.), accom- 

 have published of theFaunfe inNoTT's panied with a map and illustra- 

 and GLIDDON'S Types of Mankind tions. 



