5 
These classes are broken up into orders , each possess¬ 
ing an association of structural characters which is common 
to all the individuals included in it, and in which they differ 
from all others in their class. These orders have been dif¬ 
ferently constituted and arranged, according as different 
points have been made use of for their determination. 
They are again divided into smaller groups called families , 
which, possessing the characteristic structure of their order , 
yet depart in some minor consideration from its type—or, in 
other words, from that form which has been taken to show 
most clearly the peculiarity of the order. 
Families are again broken up into genera , which bear to 
them much the same relation as that which they, in turn, 
bear to orders. Thus—to illustrate with a familiar example— 
the lion, tiger, leopard, &c., are all cats and belong to one 
genus— Felis ; they are classified as follows:— 
Division Vertebrata —because they have a backbone or ver¬ 
tebral column. 
Class Mammalia —because they have organs peculiar to 
those vertebrates which suckle their young. 
Order Carnivora —because their plan of structure is that 
possessed by mammals which live on flesh. 
Family Felidce —because, in addition to the above, they 
possess in common certain details of teeth, claws, and other 
structural points, which none of the other carnivora share. 
Genus Felis —because certain minor modifications are un¬ 
like those existing in a few other individuals, which so far 
have agreed with them, but which now become another genus 
of the same family. 
But to go a step farther—the lion, tiger, and leopard, 
though so far they have been precisely similar, are yet recog¬ 
nizable—there are still smaller points of difference; they 
