MUSCULAR POWER IN BIRDS. 593 



artificial oars that have been constructed by 

 human ingenuity ; for as soon as the expanded 

 foot has impelled the water behind it, the toes 

 collapse, and while it is drawn forward it pre- 

 sents a very small surface to the opposing water. 

 Their plumage is so constructed as to prevent 

 the water from penetrating through it, and for 

 the purpose of preserving it in this condition 

 these birds are provided with an oily fluid, 

 which they carefully spread over the whole 

 surface of their bodies. The Swan, and many 

 other water-fowls, employ their wings as sails, 

 and are carried forwards on the water with con- 

 siderable velocity, by the impulse of the wind. 



Birds excel all other vertebrated animals in 

 the energy of their muscular powers. The 

 promptitude, the force, and the activity they 

 ' display in all their movements, and the un- 

 wearied vigour with which they persevere for 

 hours and days in the violent exertions required 

 for flight, far exceed those of any quadruped, 

 and implies a higher degree of irritability, de- 

 pendent probably on the great extent of their 

 respiratory functions, than is possessed by any 

 other class of animals. 



END OF VOL. I. 



VOL. I. «Q 



