EXTERNAIj anatomy. WINO EEATHERS. 85 
there exists in the middle a distinct notch, or sinuosity, 
to break the passage of the air — a structure which is 
only carried to its maximum in the bee-eaters. The 
tertials are very little longer than the secondaries, and 
hardly exceed tlie shortest of the primaries. It is thus 
obvious that nearly the whole power of the wing is 
thrown into the ten principal quills, which are those 
principally employed in all birds to cut the air, but 
which, in the present family, are most particularly 
adapted for that purpose. There is nothing materially 
different from this structure in the wings of the sea- 
swallows, as they are aptly termed, or the terns, except 
that the lesser quills are even shorter, and instead of lieing 
notched, are pointed in the middle, while the tertials 
are longer, and gradually become attenuated at the end, 
like the primaries. Such is the formation of an acu. 
ntinated wing, when seen in its full development. To 
note all the modifications that this form undergoes in 
its declension would l)e tedious, if not impossible. In 
the bee-eaters (Merops') the shorter primaries, the 
whole of the secondaries, and a part of the tertials, are 
deeply notched (fig. 42.) ; but the greater elongation 
of the two latter ranges of quills clearly shows a dimi- 
tnshed strength in the primaries, and indicates that 
these feathers are not so much called into action as they 
are in the swallows. Accordingly we observed, while 
in the south of Europe, that the flight of the Merops 
a,piasfer, although swift, was effected by very little 
niotion of the wings, and that a swallow would beat the 
Mr three times when they would only do so once. 
Their flight, indeed, is more like that which is called 
sailing, and they are enabled to do this by the greater 
G 3 
