NATURAL HISTORY. 
93 
Hearing . — They have the power of dif- 
tinguifliing founds, without any external ear, 
which would not only impede their flight, 
but render them liable to many injuries in 
darting through bulhes, briars. See. 
Smelling . — Their frent is fo very acute and 
extenfive, by which they are apprifed of the 
approach of their natural, as well as artificial 
enemies, that thofc who decoy ducks are 
obliged to keep a piece of burning turf in 
their mouths, to prevent being difeover- 
ed. 
Internal Strudure . — The bones, which are 
formed fufficiently ftrong to fupport the 
weight of the body, and the fyftem of its 
fiinftions, are fo light, as to be fcarcely any 
additional burthen to the flelh. All their in- 
ternal Ib-ufture is calculated to increafe the 
fnrface beyond the proportion of the folidity 
of their bodies. In older to render them 
lighter than the fame portion of air. The 
lungs and ends of the windpipe branches im- 
j bihe air into a number of bladder receptacles. 
I The crop, which is the repolitory for fuper- 
j fluous food, fupplies them in long flights, and 
other times of indifpenlible neceflity. Their 
food, being generally dry, hard, and crude, 
they have a giziai'd, which, with the help of 
fand, and other ftony particles they fwallow, 
aids them in digeftion. 
Moulting . — Although birds, from the fim- 
plicity of their ftrufture, habitation of the 
air, and perpetual exercife, are lefs lubjeft 
to 
