406 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 Passeres. By Alfred R. Wallace. 
The Passeres, 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 
difference 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. Carus, in his c Handbuch der Zoologie/ divides 
the Passeres into twenty-eight families, while Professor Sun- 
devall, in his f 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. 
Eor a long time the Tyrants of America were united with the 
Shrikes of the Old World, while such an acute ornithologist 
as the late Prince Charles Bonaparte confused and inter¬ 
mingled the genera of Timaliidse and Pycnonotidse. 
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 
