36 
ON THE CLASSIFICATION OP BIRDS. 
analogous to the external ears of quadrupeds ; the outer 
surface being convex, and the inner concave. These 
egrets, strictly speaking, are confined to one of the most 
typical genera of the owls ; hut more than one species of 
lark, and the double-crested cormorant of Hudson’s Bay*, 
have tufts of feathers analogous to the egrets of the 
owls ; but they are obviously no more than simple orna- 
mental crests, much more slender, and without any 
breadth or concavity behind. It is no argument against 
the supposition just mentioned to say, that if the egrets 
possessed by some of the owls were essentia! to their 
sense of hearing, nature would have bestowed these 
appendages upon the whole of the family, and not have 
restricted them to only one genus. This, in fact, is the 
rock upon wdiich shallow naturalists, and partial rea- 
soners, are continually splitting. They seem to forget 
tliat Nature, throughout her works, produces the same 
effect by different means, as if she delighted in every 
mode of variety. It will subsequently appear, that of 
the whole family of Strigida, Strix and Otus are the 
most typical genera ; that is to say, they possess the 
sense of hearing far more perfect than any of the other 
ow'ls ; and yet this sense, which is probably equal in 
both, is produced by very different structures. In Strix 
the ear is enormously large, and protected by a lid or 
operculum, but there are no egrets. In Otus, on the 
other hand, the. egrets are very large, but the size of 
the ear is reduced nearly one half, and has no oper- 
culum : thus, by a balance of powers, the faculty in 
both is probably equalised. 'I'he rest of the owls are 
more or less diurnal ; their eyesight does away with the 
necessity of acute hearing, and they have consequently 
small ears and no egrets. This equalisation of faculties, 
in short, is one of the most beautiful laws of the 
creation. 
(4.5.) W e now come to the second class of crests, or 
those which we have termed concealed. Like the first, 
they are moveable, and can be shut or expanded at 
* Carbo Dilophus, Sw. North. Zool. vol. ii. p. 47S. 
