to the similarity of the animal to ourselves.  Thus we can educate many of our higher mammals by a system of rewards and punishments, and we seem therefore to have good reason to believe that fear and joy, anger and desire, certain powers of perception and inference, are in their minds similar to our own.  But fear in a fish is certainly a much dimmer apprehension of danger than in us, even if it deserves the name of apprehension.  And the mental state which we call “alarm” in a fly or any lower animal is very difficult to clearly imagine or at all express in terms of our own mind.

Some investigators have made the mistake of projecting into the animal mind all our emotions and complicated trains of thought.  Thus Schwammerdam apparently credits the snail with remorse for the commission of excesses.  Others go to the other extreme and make animals hardly more than mindless automata.  We are warned, therefore, by our very mode of study, to be cautious, not too absolutely sure of our results, nor indignant at others who may take a very different view.  And yet by moving cautiously and accepting only what seems fairly clear and evident we may arrive at very valuable and tolerably sure results.

The human mind, and the animal mind apparently, manifests itself in three states or functions.  These are intelligence, the realm of knowledge; susceptibility, the realm or state of feelings or emotions; will, the power or state of choice.  Let us trace first the development of intelligence or the intellect in the animal.  Let us try to discover what kinds of knowledge are successively attained and the mode and sequence of their attainment.  Hydra appears to be conscious of its food.  It recognizes it partially by touch, perhaps also by feeling the waves caused by its approach.  It seems also to recognize food at a little distance by a power comparable to our sense of smell.  Stronger impacts cause it to contract.  It neither sees nor hears; it probably does little or no thinking.  Its knowledge is therefore limited to the recognition of objects either in contact with, or but slightly removed from, itself.  And its recognition of the objects is very dim and incomplete, obtained through the sense of touch and smell.

A little higher in the animal world a rude ear has developed, first as a very delicate organ for feeling the waves caused by approaching food or enemies; only later as an organ of hearing.  Meanwhile the eye has been developing, to perceive the subtle ether vibrations.  The eye of the turbellaria distinguishes only light from darkness, that of the annelid is a true visual organ.  Now the brain can begin to perceive the shape of objects at a little distance.  Touch and smell, hearing, sight; such is sequence of sense perceptions.  The sense-organs respond to continually more delicate and subtle impacts, and cover an ever-widening range of more and more distant objects.  Up to this point intelligence has hardly included more than sense-perceptions.