INTRODUCTION. 



In the family of the sciences Comparative Psychology may 

 claim nearest kinship with Comparative Anatomy : for just 

 as the latter aims at a scientific comparison of the bodily 

 structures of organisms, so the former aims at a similar com- 

 parison of their mental structures.* Moreover, in the one 

 science as in the other, the first object is to analyze all the 

 complex structures with which each has respectively to deal. 

 When this analysis, or dissection, has been completed for as 

 great a number of cases as circumstances permit, the next 

 object is to compare with one another all the structures which 

 have been thus analyzed ; and, lastly, the results of such 

 comparison supply, in each case alike, the basis for the final 

 object of these sciences, which is that of classifying, with 

 reference to these results, all the structures which have been 

 thus examined. 



In actual research these three objects are prosecuted, not 

 successively, but simultaneously. Thus it is not necessary 

 in either case that the final object — that of classification — 

 should wait for its commencement upon the completion of 

 the dissection or analysis of every organism or every mental 

 structure that is to be found upon the earth. On the con- 

 trary, the com2Jarison in each case begins with the facts that 

 are first found to be com^arcihU, and is afterwards pro- 

 gressively extended as knowledge of additional facts becomes 

 more extensive. 



Now each of the three objects which I have named affords 



* The word " structure " is used in a metaphorical sense when applied to 

 mind, but the usage is convenient. 



