to them, in the pointing of young pointers and the setting of young
setters in the peculiar manner of flight of certain breeds of the
pigeon, &c. We have analogous cases with mankind in the inheritance of
tricks or unusual gestures, to which we shall presently recur. To those
who admit the gradual evolution of species, a most striking instance of
the perfection with which the most difficult consensual movements can
be transmitted, is afforded by the humming-bird Sphinx-moth
(_Macroglossa_); for this moth, shortly after its emergence from the
cocoon, as shown by the bloom on its unruffled scales, may be seen
poised stationary in the air, with its long hair-like proboscis
uncurled and inserted into the minute orifices of flowers; and no one,
I believe, has ever seen this moth learning to perform its difficult
task, which requires such unerring aim.
When there exists an inherited or instinctive tendency to the
performance of an action, or an inherited taste for certain kinds of
food, some degree of habit in the individual is often or generally
requisite. We find this in the paces of the horse, and to a certain
extent in the pointing of dogs; although some young dogs point
excellently the first time they are taken out, yet they often associate
the proper inherited attitude with a wrong odour, and even with
eyesight. I have heard it asserted that if a calf be allowed to suck
its mother only once, it is much more difficult afterwards to rear it
by hand.[103] Caterpillars which have been fed on the leaves of one
kind of tree, have been known to perish from hunger rather than to eat
the leaves of another tree, although this afforded them their proper
food, under a state of nature;[104] and so it is in many other cases.
The power of Association is admitted by everyone. Mr. Bain remarks,
that actions, sensations and states of feeling, occurring together or
in close succession, tend to grow together, or cohere, in such a way
that when any one of them is afterwards presented to the mind, the
others are apt to be brought up in idea. [105] It is so important for
our purpose fully to recognize that actions readily become associated
with other actions and with various states of the mind, that I will
give a good many instances, in the first place relating to man, and
afterwards to the lower animals. Some of the instances are of a very
trifling nature, but they are as good for our purpose as more important
habits. It is known to everyone how difficult, or even impossible it
is, without repeated trials, to move the limbs in certain opposed
25