VI 
PREFACE. 
dotes of the display of animal intelligence, their books 
are valueless as works of reference. So much, indeed, is 
this the case, that Comparative Psychology has been vir- 
tually excluded from the hierarchy of the sciences. If we 
except the methodical researches of a few distinguished 
naturalists, it would appear that the phenomena of mind 
in animals, having constituted so much and so long the 
theme of unscientific authors, are now considered well- 
nigh unworthy of serious treatment by scientific methods. 
But it is surely needless to point out that the phenomena 
wdiich constitute the subject-matter of Comparative Psy- 
chology, even if we regard them merely as facts in Nature, 
have at least as great a claim to accurate classification as 
those phenomena of structure which constitute the sub- 
ject-matter of Comparative Anatomy. Leaving aside, 
therefore, the reflection that within the last twenty years 
the facts of animal intelligence have suddenly acquired a 
new and profound importance, from the proved probability 
of their genetic continuity wi f h those of human intelli 
gence, it would remain true that their systematic arrange- 
ment is a worthy object of scientific endeavour. This, 
then, has been my first object, which, otherwise stated, 
amounts merely to passing the animal kingdom in review 
in order to give a trustworthy account of the grade of 
psychological development which is presented by each 
group. Such is the scope of the present treatise. 
My second, and much more important object, is that of 
considering the facts of animal intelligence in their rela- 
tion to the theory of Descent. With the exception of 
Mr. Darwin’s admirable chapters on the mental powers 
and moral sense, and Mr. Spencer’s great work on the 
Principles of Psychology, there has hitherto been no 
earnest attempt at tracing the principles which have been 
probably concerned in the genesis of Mind. Yet there is 
