INTRODUCTION 3 
struggling. Animal psychology blossomed into an experi- 
mental science, proud of her new growth and often looking 
back with something of scorn upon the days of her infancy. 
The position of animal psychology among the sciences is, 
however, a somewhat peculiar one. Concerning the con- 
scious life of animals as distinguished from the objective 
facts of behavior—the life which falls within the peculiar 
province of psychology as distinguished from physiology— 
our knowledge rests upon an insecure foundation. We have 
no means of cognizing directly the conscious states of any 
creature besides ourselves and what we know of the psy- 
chology of our fellow human beings is based upon what we 
find taking place in our own minds. We infer conscious- 
ness in other beings because we are conscious ourselves, 
and we judge of the mental states in the minds of others, 
such as joy, sorrow, anger, or fear, from certain physiolog- 
ical manifestations which are like the accompanying mani- 
festation of these mental states in ourselves. With beings 
much like ourselves our inferences may be fairly accurate. 
When thrown amid the people of other nations or races 
our judgments are more apt to be erroneous. And when 
we try to infer what goes on in the mind of a cat or a 
dog the difficulties are very greatly increased. We may 
feel convinced that the sensations of these animals and 
even the basic emotions, such as fear, anger, etc., are 
very similar to our own, but the difficulty of ascertaining 
what sort of intellectual life one of these creatures enjoys 
is evinced by the very different interpretations of the 
subject which have been made by competent psychologists. 
If we try to imagine what sort of psychic states are as- 
sociated with the supra-cesophageal ganglion of an ant or 
a crayfish, analogy almost completely fails us. . However 
much we may learn about the behavior of these creatures, 
