Pat) OTE GY 
Introduction. 
Zootoey—from the Greek zdon, an animal, and logos, a discourse—is the 
branch of Natural History which treats of animals. In the largest sense 
of which the term is capable, it may be held to include man as part of 
its subject; but the term-is not in general thus employed. Yet man 
has much in common with the lower animals; and a knowledge of human 
anatomy and physiology is necessary for the successful study of the 
structure of animals and the phenomena which life displays in them. 
Of the three kingdoms of nature two are classed together as organic—the 
animal and the vegetable, the mineral being set apart as inorganic. Both 
plants and animals consist entirely of organs, and internal movements are 
kept up by fluids in cells and vessels, during the whole existence of the 
individual. It is not easy to define the term animal, familiar as is the’ 
idea conveyed by it. If we say that an animal is a creature having life, 
our definition is not perfect, for plants also have a kind of life, although 
we readily note a great difference between it and that which belongs to 
animals. When we study the lowest forms that nature presents to us in 
both kingdoms, it is sometimes difficult to determine to which kingdom 
a particular kind of creature belongs, although it is probable that our 
difficulty may be, owing to our imperfect acquaintance with the subjects 
of our study, for no such difficulty is felt as to any of the higher kinds, 
the phenomena of whose life are better known to us. Perhaps the power 
of voluntary motion ought to be regarded as the true distinguishing 
characteristic of animals. When we think of animal life, we always 
associate with it the idea of mind—of a will, and feeling, or a capacity 
of pleasure and pain. To plants we do not ascribe will or feeling, even 
in the lowest degree. We associate no such idea even with the pheno- 
mena of irritability in the sensitive plants, or in flowers expanding under 
the sunshine, and turning toward the sun. If there be another distinction 
universally subsisting between animals and plants, it is that animals feed 
only on vegetable or animal substances; whereas the whole nutriment 
