282 FEET OF AQUATIC lilliU-. 



ing or flight; though they also admit of modification. 

 . Thus, it' the sea-bird alights only on solid surfaces, it 

 requires the feet to be somewhat different than if it 

 alighted on soft ones ; and if it dash at once down 

 on the water from high flight, it requires the feet to 

 be different from what would be more convenient if 

 it launched itself in a direction nearly parallel to the 

 surface. Also if the bird is in the habit of walking 

 much, it is necessary that the feet should retain a 

 considerable degree of that action of all the joints- in 

 one plane, which we have already shown to be neces- 

 sary to the stability of a walking motion. If the bird 

 combines the three motions of walking, flying 1 , and 

 swimming, in nearly equal perfection (and there are 

 many birds which do so combine them), it is necessary 

 that the feet should have a different structure ; and 

 if the motion is in the water only, the structure of the 

 feet requires still to be modified according as it is 

 more of a straight forward motion, or of an ascending 

 and descending one. 



There is, however, no bird with webbed feet which 

 can have that perfect adaptation of the feet for walk- 

 ing, which is possessed by ground birds upon land ; 

 because every bird with webbed feet is a swimmer : 



