BIRDS OF OLD 57 



further notice, but the larger was remarkable in many 

 ways. Hesperornis, the western bird, was a great diver, 

 in some ways the greatest of the divers, for it stood 

 higher than the king penguin, though more slender and 

 graceful in general build, looking somewhat like an 

 overgrown, absolutely wingless loon. 



The penguins, as everyone knows, swim with their 

 front limbs we can't call them wings which, though 

 containing all the bones of a wing, have become trans- 

 formed into powerful paddles; Hesperornis, on the 

 other hand, swam altogether with its legs swam so well 

 with them, indeed, that through disuse the wings 

 dwindled away and vanished, save one bone. This, 

 however, is not stating the theory quite correctly; of 

 course the matter cannot be actually proved. Hesperor- 

 nis was a large bird, upwards of five feet in length, and 

 if its ancestors were equally bulky their wings were quite 

 too large to be used in swimming under water, as are 

 those of such short-winged forms as the Auks which 

 fly under the water quite as much as they fly over it. 

 Hence the wings were closely folded upon the body so 

 as to offer the least possible resistance, and being dis- 

 used, they and their muscles dwindled, while the bones 

 and muscles of the legs increased by constant use. By 

 the time the wings were small enough to be used in so 

 dense a medium as water the muscles had become too 

 feeble to move them, and so degeneration proceeded 

 until but one bone remained, a mere vestige of the wing 

 that had been. The penguins retain their great breast 

 muscles, and so did the Great Auk, because their wings 

 are used in swimming, since it requires even more 

 strength to move a small wing in water than it does to 

 move a large wing in the thinner air. As for our 

 domesticated fowls the turkeys, chickens, and ducks 

 there has not been sufficient lapse of time for their 



