he goes too far in underrating the power of instinct.) 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 Esquimaux 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
Prof. Mobius (23. Die Bewegungen der Thiere, etc., 1873, p. 11.), 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 learnt 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 afterwards introduced; so
strongly was the idea of a violent shock associated in his feeble mind
with the attempt on his former neighbours. If a savage, who had never
seen a large plate-glass window, were to dash himself even once against
it, he would for a long time afterwards associate a shock with a
window-frame; but very differently from the pike, he would probably
reflect on the nature of the impediment, and be cautious under
analogous circumstances. Now with monkeys, as we shall presently see, a
painful or merely a disagreeable impression, from an action once
performed, is sometimes sufficient to prevent the animal from repeating
it. If we attribute this difference between the monkey and the pike
87