40G Mr. A. R. Wallace on the Arrangement of the 



at considerable expenditure of time and trouble, gave me much 

 desirable information concerning the objects of my visit pre- 

 viously to my departure from England, and also many valuable 

 hints and suggestions during the preparation of these notes. 

 I also owe my thanks to Mr. John Baker for advice which 

 proved of much assistance to us, and for his communication 

 mentioned above. 



XL. — On the Arrangement of the Families constituting the 

 Order Passcrcs. By Alfred R. Wallace. 



The Passcrcs, as now restricted, constitute nearly three fourths 

 of all known birds. They are wonderfully uniform in all es- 

 sential points of structure, while presenting endless modifica- 

 tions in external form ; and the points of resemblance and of 

 dili'crence between the several families are so numerous and 

 conflicting that their classification still remains an almost in- 

 soluble problem. As an example of the wide difference of 

 opinion on this point, we may contrast the views of two recent 

 authors. Dr. Cams, in his ' llandbuch der Zoologie,^ divides 

 the Passcrcs into twenty-eight families, while Professor Sun- 

 devall, in his 'Methodi Naturalis Avium Disponendarum 

 Tentamen,^ has no less than 107 ; and there is often the widest 

 divergence in the succession of the groups in these two sys- 

 tems. Eminent authors also differ widely as to the position 

 of a large number of genera, those which are held by some to 

 be quite unrelated being united by others in the same family. 

 For a long time the '^I'yrants of America w'cre united Avith the 

 Shrikes of the Old World, while such an acute ornithologist 

 as the late Prince Charles Bonaparte confused and inter- 

 mingled the genera of Timaliidte and Pycnonotida3. 



The characters which have been generally used by syste- 

 matists in defining the families of Passeres are the form of 

 the bill, the scutellation of the tarsi, and the varying propor- 

 tions of the toes and wing- feathers ; but most of these are 

 subject to great variation in closely allied forms, and, with 

 the exception perhaps of the second, do not aid much in de- 

 termining the affinities of the various families towards each 



