PRINCIPLES OF NATURAL ARRANGEMENT. 337 



it has all five senses ; its blood is red ; it breathes air ; its tem- 

 perature is high ; its young are produced from eggs ; it walks 

 upon two legs ; &c. &c. Here we are at once informed that this 

 unknown animal possesses all the characters peculiar to the class 

 of Birds ; since no other animals than Birds possess a covering 

 of feathers, which is inseparably connected with the whole plan 

 of their structure and economy. In the same manner, the clas- 

 sification of the Mammalia (Quadrupeds) according to their 

 teeth, proposed by Linnaeus, proves to be a very natural one, 

 although founded upon a single set of characters ; because the 

 form and number of the teeth vary with the nature of the food 

 on which the animal is intended to live ; and to make use of 

 this, a certain form of digestive apparatus is adapted ; as well as 

 a certain kind of general structure, furnishing the instruments by 

 which the food is obtained : so that these may be known to a 

 great extent from the inspection of the teeth alone. In like 

 manner the Botanist, whilst founding his arrangement upon the 

 whole group of characters which each Plant exhibits, endeavours 

 to select those, as marks for distinguishing the several divisions, 

 which are at once easily recognised, and which serve as the best 

 key (so to speak) to those which are seated within. Such cha- 

 racters are Natural, then, in proportion as they indicate general 

 conformity or difference of structure ; thus, the distribution of 

 the veins of the leaves, a character easily recognised, will in 

 general serve to distinguish Exogens and Dicotyledons from 

 Endogens and Monocotyledons; and it is therefore a very 

 natural character, serving as a key to all those which are indi- 

 cated by these terms. On the other hand, the number of 

 stamens and pistils in a flower is a purely artificial character, 

 since it gives no further certain information of the general struc- 

 ture of the plant. 



491. Another general principle of Natural classification must 

 next be pointed out. When a number of Plants or Animals are 

 associated, on account of their general resemblance to each other, 

 into a Natural group, it will be found that the characters in 

 which they agree are presented by some members of the group 

 much more prominently than by others ; and that in some they 

 are occasionally so much wanting, that these can scarcely be 



