114 ON THE CLASSIFICATION OP BIRDS. 
the most vivid hues, or glossed with rich reflections of 
gold, rendering them inferior only to the humming birds. 
Some possess considerable vocal powers ; and the notes 
of the subgenus Euphonia, as its name implies, are said 
to be particularly musical. The impossibility, however, 
of providing the tanagers with their native insect food, 
has prevented them from ever being brought alive to the 
European menageries, to which their beauty would render 
them the greatest ornaments. 
( 129 .) It might be supposed, that the internal 
arrangement of a group, distinguished by so many 
peculiarities, both of structure, colour, and geographic 
distribution, would be by no means difficult ; yet the 
very reverse of this is the case. We may safely affirm, 
indeed, that it is one of the most diflicult to be under- 
stood in the whole circle of ornithology : nature seems 
to have departed, in this group, from that uniformity 
of progression which is so prevalent in all her works : 
this remark is not applied merely to the smaller groups, 
but actually, in many instances, to the succession of 
species. The comparative strength of the bill, for 
instance, is so variable in birds of the same subgenus 
(the lowest denomination of groups that we can trace), 
that this variation, indicative of genera in other fami- 
lies, is in this no more than a discrimination of sections 
or species. Nothing can illustrate this fact more than 
the affinity between Pitylus {fig. l63. 6) and Tardivola. 
Looking to the types of each, we should say they 
did not belong even to the same subfamily ; for the 
bill of the first is nearly as large as in the hawfinches 
{Coccothraiistes'), while that of Tardivola (a) is so com- 
paratively slender, that it seems more akin to the larks 
than to the tanagers : and yet, between these two 
extremes or types, we have now before us such a perfect 
series of graduated forms, wherein not only the bill, 
but all the other subordinate characters of the two 
groups, progresses in such a beautiful and almost im- 
perceptible manner, that we are actually at a loss to 
know where Tardivola ends, and Pitylus begins. No 
