696 



WHITE-BILLED NORTHERN DIVER. 



latter it is at least predominant, but further south, as well as in the 

 Great Slave Lake district, it meets with C. gladalis ; no intermediate 

 forms being known. In winter it ranges through the North Pacific 

 down to Japan ; while, as already indicated, it is found throughout 

 America to the north of the Arctic circle, in summer. 



No special description of the breeding-habits or eggs of this 

 species is given by Messrs. Nelson, MacFarlane or other explorers of 

 the Fur countries, but in all probability they do not differ from those 

 of the Great Northern Diver. The 'laugh ' is said to be somewhat 

 harsher than that of its congener. The distinctions between the two 

 species have already been mentioned. 



The form and structure of the legs and feet in these Divers — 

 and also in the Grebes — are worthy of attention ; for though almost 

 useless on land, these members are most efficient instruments in 

 the water. The bones, which are broad and flat, are almost as thin 

 as the blade of a knife, so that when the backward stroke in swim- 

 ming is given, the whole surface of these bones and their investing 

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

 is advanced, in order to renew the impulse, the sharp edges only 

 are opposed to the fluid : the position as well as the partially 

 rotatory motion reminding the observer of the action of oars in 

 rowing when " feathered." Those who have the opportunity of 

 examining the legs of a Diver— in a recently-killed specimen, 

 while all the parts retain their perfect flexibility — will find a beauti- 

 ful example of animal mechanics. The figure below represents the 

 form of the foot in this genus. 



