82 ON THE CLASSIFICATION OF BIRDS. 
(76.) The spurious quills are constructed precisely 
the same as the others. Their number coincides ex- 
actly with those of tlie primaries, that is, ten ; but they 
are of so many different lengths, that no author has yet 
determined either their number or their office. Taken 
collectively, they assume the shape of a somewhat ir- 
regular fan, the two first being very small, the third 
and fourth longest, and the rest diminishing in length 
until they become equal to, and join with, the greater 
covers; they are remarkably stiff, considering their short- 
ness, and they are unquestionably intended to strengthen 
and cover the base of the ten primary quills, as being 
those which are the most important to tlie power of 
flight, and require the most effective support. The 
greater wing covers, in fact, do not cover the greater 
quills, but merely the lesser ; for, as they approach the 
greater, they take a curved direction, and merely reach 
sufficiently far to lay over the base of tlie spurious 
quills. 
(77.) The formation of the wing, in reference to 
its office, depends almost entirely upon the arrangement, 
the proportion, and the shape of the quills ; and these 
again determine the powers of flight. The three sub- 
jects are thus so intimately connected that they will lose 
their chief interest unless they are treated of together. 
Between a swallow and a turkey, the most familiar in- 
stances that can be adduced of the rapidity and the 
difficulty of flight, there are innumerable modifications 
of the same power, tlie most striking of which will 
alone be noticed. The greatest powers of flying are 
enjoyed by the different groups which belong to, or 
represent, the natatorial order, to which alone those 
birds are confined which catch their food in the air. 
The albatrosses, frigate-birds, and petrels, are conse- 
quently the most expert flyers in the feathered creation. 
In the fissirostral tribe, which is the natatorial type of 
the perchers, we see the same faculty given in a pre- 
eminent degree to the swallows, swifts, night-jars, and 
bee-eaters ; and in this manner we may trace the same 
