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ON THE CLASSIFICATION OF BIRDS. 



the two or three outermost feathers 

 slightly graduated ; that is, progressively 

 shorter than those more in the middle : 

 sometimes the external feather alone is 

 abbreviated, as in the robin ; but in the 

 stone-chat {Saocicola rubicola), the four 

 outermost feathers {fig. 49.) are progres- 

 sively shortened. The tails, however, of 

 I both these birds present a union of two 

 forms, for they are rounded, and at the 

 W Wmsl^ same time exhibit the divaricated struc- 

 ture, hereafter noticed. 



(91.) 3. A fan-shaped tail, as its name implies, is so 

 much rounded that the two middle feathers are alone 

 equal in length, all the others gradually, but gently dimi- 

 nishing. A fan- shaped tail is always longer than usual, 

 and the feathers, besides being broad, have this peculi- 

 arity, that the two webs are more equal in breadth than 

 in simply rounded tails. This will be evident on com- 

 paring one of the feathers of the robin with another of 

 the fan-tailed flycatcher of New Holland : in the first the 

 shaft appears close to the edge, whereas in the other, 

 it is nearly central. This distinction, hitherto neg- 

 lected, is important, because it enables us to detect a 

 habit of the bird, from its mere skin, which, otherwise 

 could only be known by seeing the subject alive, and 

 even then, under particular circumstances. This struc- 

 ture, however rare among the perchers, is seen in the 

 highest development in the peacocks and the turkeys, 

 where the tail is of the most gorgeous and splendid 

 beauty. It may be considered a law of nature, that all 

 fan-tailed birds are representations of the Rasorial type, 

 since every one wdiose affinites have been investigated 

 have proved to be so. 4. Graduated tails not only ex- 

 hibit a greater degree of circularity than those which 

 are simply rounded, but they possess this peculiarity, 

 that the external feathers, instead of being very slightly 

 shorter than those of the middle, are abruptly abbre- 

 viated, so that the outermost is often not one third 



