CHAPTER I. 



ON ZOOLOGICAL CLASSIFICATION. 



1. THE principles of a Natural arrangement of Plants or 

 Animals having been elsewhere fully explained (BOTANY, 

 Chap. I.), it will not be necessary to do more in this place than 

 recapitulate them, with some additional illustrations of a Zoo- 

 logical character. 



2. The object of all Classification has been shown to be, 

 to bring together those beings which most resemble each other, 

 and to separate those that differ. In this manner we greatly 

 shorten the labour which would be otherwise required from the 

 Naturalist ; since, instead of spending his time and attention in 

 the study of all the characters which each specimen presents, he 

 is at once able, by knowing its general position in the Animal 

 scale, to see (as it were) intoits interior; so that a single character 

 often becomes the key to a great number. Thus, for instance, 

 if we meet with an animal covered with feathers, we know that it 

 must belong to the class of Birds ; because no other animal than 

 a Bird is endowed with this covering. And when we know it 

 to be a Bird, we can at once attribute to it all those characters 

 by which the members of this group are distinguished. Thus, 

 we feel a certainty that it has a bony skeleton covered with 

 flesh ; that of this skeleton, a jointed back-bone forms the essen- 

 tial part ; that this back -bone contains a spinal marrow, swelling 

 at its upper end into a brain, which is inclosed within a bony 

 casing or skull ; that it is oviparous, or propagates by eggs ; 

 that it breathes air by means of lungs ; that its heart has four 

 cavities ; that the blood is red, and its circulation rapid, and ar- 

 ranged on the same plan with that of Man ; that the temperature 



