2 INTRODUCTION. 
We know that a bird eats, moves, and breathes, and that 
its blood circulates; but plants also eat, respire through 
their leaves, have a circulation of sap, and some are 
endowed with locomotive powers. When we descend to 
the lower forms of animal and vegetable life, the points 
of similarity become almost identical; the swift-mov- 
ing diatom so resembling some of the lowest animal 
forms that it is well-nigh impossible to distinguish be- 
tween them. The plants, however, have no nervous sys- 
tem, no special organs of circulation or digestion that 
characterize the majority of animal forms, so that an ani- 
mal differs mainly from a plant in possessing, as a rule, 
a nervous system and special organs of circulation and 
digestion. ; 
Classification.—The animal kingdom, that is esti- 
mated to contain one fourth of a million species, is sepa- 
rated into two primary divisions: the Protozoa, or single- 
celled animals, and the Aefazoa, or those composed of 
many cells. The latter are separated into eight branch- 
es: Porifera, Calenterata, Echinodermata, Vermes, Mollus- 
ca, Arthropoda, Tunicata, Vertebrata, These are in turn 
divided until the varied forms are grouped, like with 
like. This end is attained by comparison, and the result 
is termed classification. Thus the dog, as distinguished 
from a plant, is placed primarily in the animal Aingdom. 
Possessing a backbone, it is placed in the branch of 
vertebrate animals. It differs from the fishes, reptiles, 
and birds, by giving milk; hence it is placed in the 
class of mammals. Continuing our comparisons, we find 
that, with the lions, tigers, and cats, it is a flesh-eater, 
and so is placed in the order carnivora. From its gen- 
eral appearance and form, it is associated with others 
in the family of dogs. With others that have a similar 
structure, it is given the generic name canis; then, to 
distinguish what kind of a dog it is, wild or domestic, it 
is given a specific or specifying name, as the common 
