406 The Bird 
One interesting analogy to the fin of a fish is found 
in the tail of the Blue Duck of New Zealand. This bird 
lives in swift mountain streams and when swimming carries 
its long tail entirely submerged. By vigorous sidewise 
flicks of these tail-feathers it can turn around, as if on a 
pivot, without being carried down-stream, even when 
in the centre of a rapid, swirling current. 
Fic. 322.—Murre showing tail. (Compare with Fig. 246.) 
It is interesting to compare this use of the tail-feathers 
with the function of the tail in the fhghtless penguins. 
In the Black-footed species, at least, the tail-feathers are 
stiff and short, but the bones of the tail are unusually 
elongated and the flesh which covers them is flattened 
into a kind of vertical rudder. Strong muscles control 
