xxviii 
which this species is found, that will explain the necessity of 
it, or account for its presence, or is there any peculiar power 
or faculty possessed by this bird of which those allied to it 
are deprived? or are we to regard it as one of those examples 
of creative omnipotence which often displays itself in the va- 
riety of its works, without any other obvious result but the 
mere manifestation of that power ?—a remark which appears 
strongly verified by many of the peculiarities of the living 
productions of Australia. 
Dr. Knox considers that the emu has been furnished with 
this peculiar provision to preserve it amidst those dangers 
from sudden floods to which New Holland is particularly 
exposed. ‘ The sandy plains of this country,” he says, ‘are, 
during a great part of the year, inundated, and become then 
boundless marshes ; and the plains generally are exposed to sud- 
den inundations. The rivers, moreover, running westward from 
the great chain of mountains, terminate in vast muddy inland 
marshes ; the emu, forced to seek his food amidst these fens, 
may, when obliged to have recourse to swimming (which 
must often be the case), fill the muscular bag of the trachea 
with air, and thus convert it intoa swimming bladder. It may 
also assist the bird in escaping from his pursuers; but on this 
I do not mean to insist, as this organ is wanting in the galea- 
ted cassowary and in the ostrich, both equally remarkable for 
speed of foot.” Dr. Knox further remarks, that when the 
bag has been distended by an expiratory effort, and the glottis 
retained in a closed state, the air may be alternately circu- 
lated between the lungs, air-cells, and tracheal bag, without 
the bird being necessitated to allow it to escape, in order 
again to perform the act of inspiration, and thus give it an 
additional advantage in running. ‘This explanation appears 
extremely probable, and, no doubt, if the inspiratory efforts 
are thereby rendered less frequent, this creature may be ena- 
bled to sustain its running flight (which, in speed, is said to 
surpass the race-horse or the grey-hound) for a longer time, 
