THE CLASSIFICATION OF ANIMALS. 235 
But there are types within types. Thus, there are five 
modifications of the Yertebrate type — Fish, Amphibian, 
Reptile, Bird, and Mammal; and these are again divided 
and subdivided, for Mammals, e. g., differ among them¬ 
selves. So that in the end we have a constellation of 
groups within groups, founded on peculiar characters of 
less and less importance, as we descend from the general 
to the special. 
Individuals are the units of the Animal Creation. An 
animal existence, complete in all its parts, is an individual, 
whether separate, as Man, or living in a community, as the 
Coral. 127 
Species is the smallest group of individuals which can 
be defined by distinct characteristics, and which is sepa¬ 
rated by a gap from all other like groups. A well-marked 
subdivision of a species is called a variety. Crosses be¬ 
tween species are called hybrids , as the Mule. 
Genus is a group of species having the same essential 
structure. Thus, the closely allied species Cat, Tiger, and 
Lion belong to one genus. 
Family, or Tribe, is a group of genera having a simi¬ 
lar form. Thus, the Dogs and Foxes belong to different 
genera, but betray a family likeness. 
Order is a group of families, or genera, related to one 
another by a common structure. Cats, Dogs, Hyenas, and 
Bears are linked together by important anatomical features; 
their teeth, stomachs, and claws show carnivorous habits. 
Class is a still larger group, comprising all animals 
which agree simply in a special modification of the type 
to which they belong. Thus, Fishes, Amphibians, Rep¬ 
tiles, Birds, and Mammals are so many aspects of the Yer¬ 
tebrate type. 
Subkingdom is a primary division of tlie Animal King¬ 
dom, which includes all animals formed upon one of the 
various types of structure; as Yertebrate. 
