774 The American Naturalist. [August, 
Their points of difference are essentially qualitative and cannot be es- 
timated as quantities or magnitudes. 
One convenient method of avoiding such illegitimate interpretations 
is found in the careful study of the physiological conditions of con- 
sciousness. We are justified in assuming that sense organs of the same 
character mediate sensations of the same kind, and if we find any wide 
difference in the structure of the organs we must be cautious in our in- 
terpretations. It is probable, for example, that the conscious states 
mediated by the composite eye of the insect cannot be translated into 
any terms drawn from our visual consciousness. It follows, then, that 
to the bee or the fish, the hive and the water is not at all like that 
which we understand by those words. And the same is true even of 
that most general condition of all perception—space. It is probable 
that few animals have what we know as space, yet all probably have 
some analogue which bears tò their total consciousness the relation 
that space bears to ours. 
Similar inferences may be die with reference to common or bod- 
ily sensation. As it depends upon bodily structure we can scarcely 
suppose that the body of an insect yields a sensation-total to its pos- 
sessor at all like that which our body yields us, and since emotions de- 
pend upon variations in the composition of this bodily sensation, we 
cannot assume that the ant, when he attacks or runs away from his 
enemy, experiences what we call fear or courage. Yet he experiences 
analogous emotions. 
A careful description of the phenomena of organization and life from 
the biological or external point of view must, therefore, precede any at- . 
tempt at an interpretation of their psychological significance, and, as 
the former has never been done, the attempts made at the latter are of 
little value. Especially must we discard the current antithesis between 
“human” and “animal” psychology. As there is no structure com- 
mon to all “ animals,” so, too, is there no mind common to all animals: 
If we are to draw antitheses at all, it would be better to speak of the 
“insect mind,” the “ vertebrate mind,” since the gulf between the 
human mind and that of other vertebrates is probably not as great as 
that between the mind of vertebrates and that of insects. We must, in 
other words, study morphological types of mind, just as we study simi- 
lar types of body. 
While the method above outlined has not been followed, and the 
nature of the sensibility of the lower animals has, in consequence, 
never been thoroughly understood, their acts have been very carefully 
studied. Unfortunately, the inquiry has been prosecuted from the 
