BLACK-THROATED DIVER. Ill 



flanks and under tail-coverts dusky ; legs and toes dark 

 brown outside, lighter pale brown within. The whole length 

 is about twenty-six inches ; wing from the carpal joint to the 

 end of the primaries, eleven inches and a half. Weight 

 from 4i to 5|- lbs. Females are but little smaller than 

 males, and both sexes, when mature, have the throat black. 

 The Divers undergo a partial moult in the spring, and the 

 black-throat on its first assumption is generally varied with 

 a few white feathers. 



A young Black- throated Diver obtained at Nagasaki on the 

 25th of December has the bill dark horn-colour ; the upper 

 part of the head and neck ash-brown ; the part below the 

 eye, throat, and underparts dull white ; upper parts blackish, 

 the upper wing-coverts showing small white spots as in the 

 adult ; axillaries white ; flank-feathers ashy-brown. 



Young birds measure twenty-three or twenty-four inches 

 in length, and, except in size, they resemble the young of 

 the Northern Diver ; the back of the neck is, however, of a 

 much purer grey, and there are none of the indications of 

 the neck-bands noticeable in the latter. 



The form and structure of the legs and feet in these 

 Divers, and also in the Grebes, arc worthy of particular 

 examination. Though almost useless on land, these mem- 

 bers 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 legs of a Diver, 

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

 perfect flexibility, will find a beautiful example of animal 

 mechanics. 



