106 ON THE CLASSIFICATION OF BIRDS. 
the flat direction in which this member is carried by 
ordinary birds. A compressed tail, however, is even 
more concave than the latter are convex : the lateral 
feathers, instead of being directed upwards, diverge 
downwards, while those of the centre are the most ele- 
vated. But not to perplex the reader with a more 
technical definition, he has only to look to the tail of a 
domestic fowl to gain a clear knowledge, at least of the 
appearance, of the structure we should fully describe 
but for so familiar an example. There are few in- 
stances, however, out of the genus Gallue, where this 
particular structure is met with. Among the perching 
birds, we only know of the two species composing the 
genus Alecturue, and certain males of the VVid.au 
finches ; but these latter lose their singular-shaped 
tail feathers after the breeding season. 
(100.) 13. Fasciculated, or plumed tails, are still more 
rare than any of those we have now enumerated : the 
feathers do not, to all appearance, lay in any regular or 
determinate order, but rather give the idea of being 
fasciculated, or formed into a bunch. Such is the tail 
of the ostrich ; while the plume-tailed honeysucker of 
Southern Africa seems to have the feathers equally 
irregular, but upon closer examination this is not found 
to be the case : they are inserted in the ordinary 
manner, but the central feathers are so long, and so 
flexible, that, instead of retaining their right i)osition in 
the series, they fall over each other, and thus assume 
the appearance of being fasciculated at their base. 
(101.) 14. A scnnsorinl tail is perhaps of more es- 
sential importance to the birds which possess it, than 
any other modification of this member is to other birds ; 
at least, it will ajjpear so because we know more of its 
particular functions than of any other. Its form, as be- 
fore remarked, is generally cuneated, but it is sometimes 
rounded, and in a few birds we have instances of a 
scansorial tad being quite even. Its distinguishing 
peculiarity, however, rests on the structure of the shaft, 
which is at all times remarkably stiff, and in some in- 
