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 Metazoa, or those composed of 

 many cells. The latter are separated into eight branch- 

 es : Porifera, Ccelenterata, 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 kingdom. 

 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 cam's; then, to 

 distinguish what kind of a dog it is, wild or domestic, it 

 is given a specific or specifying name, as the common 



