In these pages, the term "animal" is not used in its most common
and most restricted sense. It is intended to apply not only to
quadrupeds, but also to all the vertebrate forms,--mammals,
birds, reptiles, amphibians and fishes.

For observation and study, the whole vast world of living
creatures is ours, throughout all zones and all lands. It is not
ours to flout, to abuse, or to exterminate as we please. While for
practical reasons we do not here address ourselves to the
invertebrates, nor even to the sea-rovers, we can not keep them
out of the background of our thoughts. The living world is so vast
and so varied, so beautiful and so ugly, so delightful and so
terrible, so interesting and so commonplace, that each step we
make through it reveals things different and previously unknown.

The Frame of Mind. To the inquirer who enters the field of animal
thought with an open mind, and free from the trammels of egotism
and fear regarding man's place in nature, this study will prove an
endless succession of surprises and delights. In behalf of the
utmost tale of results, the inquirer should summon to his aid his
rules of evidence, his common sense, his love of fair play, and
the inexorable logic of his youthful geometry.

And now let us clear away a few weeds from the entrance to our
field, and reveal its cornerstones and boundary lines. To a
correct understanding of any subject a correct point of view is
absolutely essential.

In a commonplace and desultory way man has been mildly interested
in the intelligence of animals for at least 30,000 years. The Cro-