Tails 407 
this, and by it the extremely quick dives and turns are 
made possible. No feather would be stiff or rigid enough 
to offer to the water the resistance which these feathered 
seals require. 
Exceptions to the rudder use in flying birds are found 
in the murres—sea-birds which share the cliffs of our north- 
ern coast with cormorants and gulls. The tail-feathers 
of a murre are so short as to be useless for steering pur- 
* poses, so in flight the bird uses its webbed feet instead, 
stretching them out behind, opening, turning, and twist- 
ing them in harmony with the wings, with as satisfactory 
results as could be desired. 
The shape of the tip of the tail varies greatly in birds. 
It may be square or rounded, or cuneate, or indented 
in the centre, or swallow-tailed, as we appropriately call 
the latter deeply forked condition. These conditions may 
be paralleled or duplicated in many different Families of 
birds. For example, the forked type is seen in our com- 
mon Barn Swallow, in those dainty relatives of the gulls, 
the terns—‘‘Swallows of the Sea,’—and again in the 
Forked-tailed Kite and the Scissor-tailed Flycatcher. 
By closely watching a swallow as it courses swiftly over 
a meadow, or shoots upward, buoying itself against the 
breeze, we can appreciate the delicate adjustment of the 
muscles which govern the tail-feathers. Each feather 
seems vital with life, now sliding one over the other until 
all are in a narrow line, then expanding, with less friction 
than ever a fan opened, into a wide-spreading, gently 
graduated fork. The quartet of forked-tailed birds men- 
tioned above are splendid fliers, but we shall see that skill 
