The brain is still enlarging, the
sense-organs bring in fuller and more definite reports of a wider
environment. Greater freedom of action by means of a stronger
locomotive system is bringing continually new and varied
experiences. And if, as in vertebrates, longer life be added,
frequent repetition of the experience deepens the impression.
Slowly, as if tentatively, the animal begins to modify some of its
instincts, at first only in slight details, or to adopt new lines of
action not included in its old instincts, but suited to the new
emergencies. This is the dawn of intelligence. Its beginnings still
remain undiscovered. Mr. Darwin believes that traces of it can be
found in earthworms and other annelids. He also tells us that
oysters taken from a depth never uncovered by the sea, and
transported inland, open their shells, lose the contained water, and
die; but that left in reservoirs, where they are occasionally left
uncovered for a short time, they learn to keep their shells shut,
and live for a much longer time when removed from the water. If
oysters can learn by experience, lower worms probably can do the
same.
Certain experiments made on sea-anemones, actinae animals a little
more highly organized than hydra, demand repetition under careful
observation.[A] The observer placed on one of the tentacles of a
sea-anemone a bit of paper which had been dipped in beef-juice.
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