SWIMMING 



an 



efficient pair of anterior (sea-lion) or posterior (seal) flippers, or 

 a properly formed tail (whale) must act obliquely against the water, 

 for the same reason that an ice boat can travel much faster quartering 

 the wind than running directly before it. This principle has governed 

 the whole course of development of all the more highly adapted aquatic 

 vertebrates. 



[23] 



