by a companionship with man, for whose use this faculty was alone
intended.

Although the animals which especially display these exceptional or
contingent instincts are those which are fitted for the use and comfort
of man and may be domesticated, it is doubtless true that many other
species are in some degree provided with them, and that they thus have
a plasticity in their nature which enables them to exercise, under
particular circumstances, unlooked-for attention, foresight, and
caution. And besides, it is only in analogy with the laws of the
physical world that instinct should admit of a slightly diversified
application.

It is to be noticed in this connection that many animals are gifted
with a wonderful sensibility of the senses,--the action of which is
sometimes mistaken not only for the action of instinct, but for that of
reason also. The acuteness of the sense of smell in the dog, which
enables him to trace the steps of his master for miles through crowded
streets by the infinitesimal odor which his footsteps left upon the
pavement, is quite beyond our conception. Equally incomprehensible to
us are the keenness of sight and wide range of vision of the eagle,
which enable him to discover the rabbit nipping the clover amid the
thick grass at a distance at which a like object would be to us
altogether imperceptible. The chameleon is enabled to seize the little
insects upon which it feeds by darting forth its wonderfully
constructed tongue with such rapidity and with such delicacy of
perception that "wonder-loving sages" have told us that it feeds upon
the air.

It has been the belief of some observers that some animals have senses