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ON THE CLASSIFICATION OF 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 ; but 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 essential 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 which shallow naturalists, and partial rea- 

 soners, are continually splitting. They seem to forget 

 that 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 Strigidce, Stria 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 

 owls ; and yet this sense, which is probably equal in 

 both, is produced by very different structures. In Stria 

 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. The 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. 



(45.) We 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. 473. 



