I THE SERVICE OF TAILS 79 
against the wall of a hollow tree, rock-crevice, or 
chimney. As a result, the end of the tail-feathers 
of such birds has become stiffened and capable of 
this special work to a remarkable degree; while in 
the case of the common chimney swift, and some 
similar, rock-climbing species of 
the East, the shafts of the 
feathers project beyond the 
vanes in long, sharp spines, 
equal in effect to the climbing- 
irons of a telegraph lineman. 
Among animals that live in 
the water, the tail becomes of 
supreme importance in loco- 
motion. The shiimp’s swim- 5°82 TBeMiNsTINe 
2 7 2 i THE TAIL-QUILLS 
ming is wholly by reaching its OF A SWIFT. 
tail out and pulling itself back- 
ward. This, of course, is the principle of the oar; 
and the shrimp is able to “feather,” since the 
plates of his tail shut up like a fan in recovering 
for a new stroke. 
It is mainly as a screw-propeller, however, that 
their tails serve the swimmers — precisely the mo- 
tion a man makes when sculling a boat by a Single 
oar held over the stern. This motion is plainly 
visible in fishes, the most swift and powerful among 
which have the smallest body-fins ; and it is solely 
by this sculling movement of the tail that the shark 
and bluefish make such terrific rushes after prey, 
that the trout is able to give the angler so much 
~ 
