334 COLYlMBrDE. 



first assumption of the Black-tliroat it is gene^'ally varied 

 with a few wliitc feathers. 



Young birds measure twenty-three or twenty-four inclies 

 in length, and closely resemble the young of the Northern 

 Diver, except in size. 



The form and structure of the legs and feet in these 

 Divers, and also in the Grebes, are worthy of particular ex- 

 amination. Though almost useless on land, these members 

 are most efficient instruments in the water. The bones are 

 broad and flat, and almost as thin as the blade of a knife ; 

 when the backward stroke in swimming is given, the whole 

 surface of all these bones and their investing membranes is 

 brought to bear against the water ; but when the leg is to 

 be brought forward again to renew the impulse, the sharp 

 edges only are opposed to the fluid, and the position, as well 

 as the partially rotatory motion, remind the observer of the 

 action of oars in rowing when used by skilful hands. Those 

 who have the opportunity of examining the leg of a Diver, in 

 a recently-killed specimen, while all the parts retain their 

 perfect flexibility, will find a beautiful example of animal 

 mechanics. 



The figure below represents the form of the foot in this 

 genus of birds. 



