SYSTEMATIC ZOOLOGY. 3 
animals, such as fishes, birds, or mammals, which have a 
backbone, are placed together in the branch or sub-kingdom 
of Vertebrates; those vertebrates, such as the cat, 'horse, 
or cow, which suckle their young, are placed in the class 
of Mammals; those mammals which have claws and teeth 
adapted for seizing and chewing flesh, i,e., are carnivorous, 
belong to the order of Carnivora. The order of Carnivora 
is composed of a number^of families, such as the cat family, 
the dog family, etc. A family is composed of a genus, and 
a genus is made up of species and varieties, the latter being 
composed of individuals. 
Thus the principle of zoological classification consists in 
placing animals which are alike by themselves into distinct 
groups. The following table expresses the zoological posi- 
tion of the cat: 
Kingdom of Animals; 
Sub-kingdom or Branch, Vertebrata; 
Class, Mammalia; 
Order, Carnivora; 
Family, FelidaB; 
Germs, Felis; 
Species, Felis domesticus; 
Variety, Angorensis; 
Individual, a single Angora cat. 
The animal kingdom is divided into two series of branches: 
those for the most part composed of a single cell are repre- 
sented by a single branch, the Protozoa (animalcules). 
Those animals whose bodies are formed of many cells are 
called Metazoa^ The series of Metazoa comprises the 
seven higher branches— 5., the Porifera, Coelenterata, 
Ecliinodermata, Vermes, Mollusca, Arthropoda, and Ver- 
teirata. Their relationships may be expressed by the fol- 
lowing 
* In the latter group the cells are arranged in two, mostly three, 
fundamental cell-layers. Of these cell-layers the outermost is called 
the ectoderm, the middle the mesoderm, the innermost Wi^ endoderm. 
