the more he attributes to reason and the less to unlearned instincts. In
future chapters we shall see that some animals extremely low in the
scale apparently display a certain amount of reason. No doubt it is
often difficult to distinguish between the power of reason and that of
instinct. For instance, Dr. Hayes, in his work on "The Open Polar Sea,"
repeatedly remarks that his dogs, instead of continuing to draw the
sledges in a compact body, diverged and separated when they came to thin
ice, so that their weight might be more evenly distributed. This was
often the first warning which the travellers received that the ice was
becoming thin and dangerous. Now, did the dogs act thus from the
experience of each individual, or from the example of the older and
wiser dogs, or from an inherited habit, that is from instinct? This
instinct may possibly have arisen since the time, long ago, when dogs
were first employed by the natives in drawing their sledges; or the
Arctic wolves, the parent-stock of the Esquimau dog, may have acquired
an instinct impelling them not to attack their prey in a close pack,
when on thin ice.

We can only judge by the circumstances under which actions are
performed, whether they are due to instinct, or to reason, or to the
mere association of ideas; this latter principle, however, is
intimately connected with reason. A curious case has been given by
Professor Möbius, of a pike, separated by a plate of glass from an
adjoining aquarium stocked with fish, and who often dashed himself with
such violence against the glass in trying to catch the other fishes,
that he was sometimes completely stunned. The pike went on thus for
three months, but at last learned caution, and ceased to do so. The
plate of glass was then removed, but the pike would not attack these
particular fishes, though he would devour others which were afterward
introduced; so strongly was the idea of a violent shock associated in