48 ON THE CLASSIFICATION OF BIRDS. 
because it is not only bare of feathers, but the orifice 
appears to have a prominent rim, lengthened into a 
wattle, which hangs down on each side of the neck. The 
conch of the ears in the common barn owl, and a few 
others, have a small lid or operculum, which partially 
closes the aperture; but this appendage hes perfectly flat, 
and is entirely hid hy the surrounding feathers. In 
describing the parts or colours of a bird, the term “ear ” 
must be considered as not strictly applying to that organ, 
but to the ear feathers, or those which cover the orifice 
of the ear itself. 
(52.) We know, either from facts, or from certain 
indications, that the sense of smell is very highly de- 
veloped in some tribes, and but very sHghtly in others. 
It has generally been supposed that vultures were at- 
tracted to their food by their sense of smell, and not by 
their sight; and this error has given rise to some ingenious 
arguments and unjustifiable personalities against Mr. 
Audubon,— the first, we believe, who called this supposed 
truth in question. The results, however, have been such as 
to enable that gentleman to silence his opponents, and 
to establish, in the most complete manner, the accuracy of 
his first assertion. We must, therefore, consider that the 
toucans, above all other birds, are the most highly gifted 
in this respect, — a fact which is not only established by 
their economy, but also by their structure ; the latter 
evidence being wholly wanting in the case of the vultures, 
whose nostrils have nothing in them to sanction a belief 
of their being more highly sensitive than those of ordi- 
nary birds. This great development of the olfactory 
nerves in the toucan is concentrated in the biU, which 
is entirely filled with a cellular tissue of nerves, somewhat 
resembling the webs of those spiders which are found in 
dark corners, being crossed and interlaced in different 
directions by thread-like nerves, all of which communi- 
cate to the two lateral openings of the nostrils, placed, 
not in the substance, hut on the sides of the bill, close 
to the front of the head. This extraordinary gift of 
smell enables these birds to discover the nests of others. 
