But the hand of even the best dead ancestors cannot always be allowed to hold the helm.  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.  It was seized and carried to the mouth and here discarded.  This tentacle after one or two experiments refused to have anything more to do with it.  But other tentacles could be successively cheated.  The nerve-cells governing each tentacle appear to have been able to learn by experience, but each group in the diffuse nervous system had to learn separately.  The dawn of this much of intelligence far down in the animal kingdom would not be surprising, for the selection and grasping of food has always involved higher mental power than most of the actions of these lowest animals.  Memory goes far down in the animal kingdom.  Perhaps, as Professor Haeckel has urged, it is an ultimate mental property of protoplasm.  And the memory of past experience would continually tend to modify habit or instinct.

  [Footnote A:  These experiments have been continued with most
  interesting and valuable results by Dr. G.H.  Parker, of Harvard
  University.]

It is unsafe, therefore, to say just where intelligence begins.  At a certain point we find dim traces of it; below that we have failed to find them.  But that they will not be found, we dare not affirm.  In the highest insects instinct predominates, but marks of intelligence are fairly abundant.  Ants and wasps modify their habits to suit emergencies which instinct alone could hardly cope with.  Bees learn to use grafting wax instead of propolis to stop the chinks in their hives, and soon cease to store up honey in a warm climate.