INTRODUCTION 7 
explaining one. But a discussion of this question in all its 
bearings would carry us too far. 
If there is no infallible test for the determination of the 
existence of consciousness in animals we are by no means led, 
as some physiologists would have us believe, to the denial 
of the possibility of a comparative psychology. If we can 
explain the behavior of lower organisms in terms of phy- 
siological laws without assuming any réle of conscious states 
in determining their acts, and were able to extend the same 
kind of explanation to higher forms until ultimately the 
whole sentient creation were embraced in our system, the 
rejection of comparative psychology would logically lead, 
as Claparéde has well shown, to the denial of human psy- 
chology as well. On the other hand, starting in with the 
assumption that human psychology is a legitimate subject 
matter for a science, there is no logical ground for refusing 
to draw inferences concerning the mental aspects of the 
behavior of apes, and other higher mammals; and if we 
can infer something of the mental life of the animals near- 
est ourselves we are warranted in extending our psycho- 
logical inferences as far down in the scale as analogy per- 
mits us to go. How far analogy warrants us in going 
is capable of but a very indefinite answer. When we 
come to ants and spiders everyone may perhaps be allowed 
to have his own opinion; and there may be a more than 
sufficient compensation for our inability to reach conclu- 
sive proofs of our views regarding the psychic life of such 
creatures in having a perennial source of contention with 
which comparative psychologists may occupy themselves 
whenever they come together. 
The existence of mind in the lower animals has something 
more than a theoretical interest. In our experiments on 
these creatures it would be unfortunate if we were mistaken 
