6 INTRODUCTIOX. 



in its pursuit many and varied points of interest, which are 

 quite distinct from any interest that may be felt in the attain- 

 ment of the ultimate end — Classification. Thus, for example, 

 the study of the human hand as a mechanism has an interest 

 apart from all considerations touching the comparison of its 

 structure with that of the corresponding member in other 

 animals ; and, similarly, the study of tlie psychological facul- 

 ties in any given animal has an interest apart from all con- 

 siderations touching their comparison with the corresponding 

 faculties in other animals. Again, just as the comparison of 

 separate bodily members throughout the animal series has an 

 interest apart from any question concerning the classification 

 of animal bodies to which such comparison may ultimately 

 lead, so the study of separate psychical faculties throughout 

 the animal series (including, of course, mankind) has an 

 interest quite distinct from any question concerning the 

 classification of animal minds to which such comparison may 

 ultimately lead. Lastly, around and outside all the objects 

 of these sciences as such, tliere lies the broad expanse of 

 General Thought, into which these sciences, in all their 

 stages, throw out branches of inference. It is needless to 

 say that of late years the interest with which the unpre- 

 cedented growth of these branches is watched has become so 

 universal and intense, that it may be said largely to have 

 absorbed the more exclusive sources of interest which I have 

 enumerated. 



With the view of furthering these various lines of interest, 

 I have undertaken a somewhat laborious enquiry, part of 

 which has already been published in the International 

 Scientific Series, and a further instalment of which is con- 

 tained in the present volume. The two works, therefore, 

 " Animal Intelligence " and " Mental Evolution in Animals," 

 although published separately, are really one ; and they have 

 been divided only for the following reasons. In the first 

 place, to have produced the whole as one volume would have 



