

IN NATURAL HISTORY 13 
It will be found that some of the animals described in books have 
not only two, but three names, and this means that they belong to a par- 
ticular race, or subspecies, of some well recognized species. It was once 
thought that species were unchangeable, and that animals were sharply 
distinguished from one another, but as they were more carefully studied, 
and more specimens were available, it became evident that individuals 
from a given part of the range or habitat of a species, might be slightly 
different from the standard—those dwelling in desert regions being a 
little paler than the majority, and those residing in damp, wooded 
localities being somewhat darker. To such local groups or geograph- 
ical races, the name of subspecies (under-kind) is applied, and the study 
of this is a part of the study of geographical distribution. 
CLASSIFICATION 
Classification is merely the orderly arrangement of animals, or other 
objects, placing those most closely related to one another in a class by 
themselves and arranging the groups thus formed with reference to their 
degree of relationship. In the case of animals, this results in the forma- 
tion of groups of varying size and importance, the principal being Species, 
Genus, Family, Order, Class, and Phylum, while for purposes of great- 
er exactness intermediate assemblages may be made, such as super- 
order, subclass, subfamily, and so on, the prefix super, above, meaing 
greater than, and sub, under, less than. 
The eatire Animal Kingdom is divided into large branches or phyla, 
a Phylum! being a large assemblage of animals that have had a commoa 
line of descent aad agree in some very imporiant character. Thus the 
classes Mammals, Birds, Reptiles, Batrachia, and Fishes form parts of the 
Branch or Phylum Vertebrata, or backboned animals, which are distin- 
guished by having a more or less complete internal skeleton of cartilage 
or bone. 
The first divisioa of aaimals was into vertebrates and invertebrates, 
according as they did or did not have a backbone, but it was sooa recog- 
nized that the iavertebrates differed among themselves quite as much as 
they did from the vertebrates. So Cuvier divided them into Radiates, 
Mollusks, and Articulates, and as our knowledge of animals has increased 
so also has the number of groups into which they are divided: for a 
system of classification is merely an expression of the present state of our 
knowledge of animals. 
1From the Greek phylon, a tribe. 
