58 
ON THE CLASSIFICATION OP BIRDS. 
repeat our opinions on this intricate question : let us 
rather illustrate it by the testimony of others. 
(6’7.) We have seen that Setophaga and Sglvicola, 
notwithstanding their intimate resemblance, stand in 
two different circles, which circles are connected by the 
subgenus Dumecola; their relation, therefore, accord- 
ing to the views of Mr. MacLeay, are merely analo- 
gical ; not because this relation is less perceptible than 
that between Sglvicola and Dumecola, but because the 
two groups stand opposite to each other in different 
circles. Now, setting aside the usual mode of dis- 
tinguishing affinities from analogies in larger groups, 
it must be at once admitted, that when the differences 
between two given groups are so imperceptibly gra- 
duated and softened down by intervening species, that 
it is utterly impossible to discover one. link that is 
imperfect in the chain, then such a relation becomes 
unquestionably one of absolute and direct affinity. 
To demonstrate, therefore, that this is true in regard to 
Sglvicola and Setophaga, we shall cite the authority of 
VTilson, a man totally destitute of theory, but who 
watched and studied these birds in their native haunts. 
Let us take the Sgloicola Americana, the blue yel- 
low-backed warbler of the American Ornithotogg 
(■i 1)1. 28. f. 3.), as the best and the most famihar ex- 
ample of the true Sglvicolee ; we see the bill l^fig. 1S3. a) 
compressed on its sides, and, although wider at the base. 
still the breadth is not greater than its height: the 
bristles of the rictus are short, and do not extend 
