Vlll INTRODUCTION. 



The intrinsic arrangement of the families contained in this volume 

 is my own ; and 1 have tried to justify it by the diagnoses of the 

 subfamilies and genera. Besides other characters hitherto not ap- 

 plied to diagnostic descriptions, the pattern of colour has frequently 

 been resorted to as a most important taxonomic feature, although 

 •' not the only character which indicates near relationship.'' 



One single character, no matter whether " structural " or not, as 

 generally used in 'Keys,' hardly ever determines the limit of a family; 

 but a greater number, the coincidence of several characters, although 

 perhaps unimportant by themselves, will suffice for this purpose. 

 Eegarding the vexed question of species, I have frequently made 

 use of the designations subspecies and races; but as their synonj-my 

 and designations have generally been kept distinct, they can easily 

 be restored to specific rank, whenever this be thought necessary, 

 the whole question being thus left as a mere matter of personal 

 opinion. Besides, it must be borne in mind that the species of the 

 various genera are not equivalent. 



I wish to tender my thanks to the following gentlemen, who 

 by the loan of specimens, or kindly permitting access to their 

 collections, have considerably facilitated the completion of this 

 volume : — H. E. Dresser, Esq., 0. Salvin, Esq., Captain "Wardlaw 

 Eamsay, Dr. Scully, Captain Shelley, H. Schalow, Dr. Reichenow, 

 and Professor Cabanis. 



Mr. Sclater put his rich collection of VireonincB at my disposal, 

 and permitted me to make the fullest possible use of his descriptions 

 and " Keys " to this difficult group. Mr. Seebohm not only gave 

 me access to his large series of birds, but also thoroughly worked out 

 and revised with me several times the Grey Shrikes, the Nuthatches, 

 and many of the Titmice. 



Finally, I beg Mr. E. B. Sharpe to accept my thanks for his many 

 acts of courtesy, not only in guiding me at the beginning of my 

 work, but also in lending me throughout his assistance in many 

 difficulties, which, without his aid, would have caused me much 

 additional labour. 



H. GADOW. 



Cambridge, 

 June 1883. 



