80 WILD NEIGHBORS CHAP. 



work, and the salmon to climb or leap up water- 

 falls, the ascent of which excites our amazement. 

 Alligators, crocodiles, and aquatic lizards, such as 

 those of India and Egypt,. have little other means 

 of progress under water, yet they are powerful 

 swimmers; the Nile monitor, in fact, can swim 

 much faster than young crocodiles of its own size, 

 of which it captures and devours large numbers, 

 by reason of the vertical flattening of its tail. 

 The profound diving of a whale, the follow-my- 

 leader bounding play of the porpoise and dolphin, 

 and the impetus for soaring gained by the flying- 

 fish, are all due to the propulsion of the tail, the 

 principle of which is embodied in the two-bladed 

 propellers of our swift steamships. Even some of 

 the diving-birds make their way under the surface 

 by closing their wings and sculling the short and 

 stiff feathers of the tail, though other diving-birds 

 paddle with their wings under the water just as 

 they fly in the air. 



In all these flying and swimming creatures, not 

 only birds and fishes, but the marine mammals and 

 the flying quadrupeds, the tail is a rudder, as well 

 as a propeller and balance. This is easily observa- 

 ble not only in the flight of any bird, but in that of 

 the flying and leaping squirrels ; and no doubt it 

 is an essential part of the apparatus for flight pos- 

 sessed by these animals, including the checking 

 and controlling of the speed, as observation of a 

 bird passing or alighting will quickly show ; while 



