324 FLAMINGOES, DUCKS, AND SCREAMERS. 



beak is comparatively straight, and more or less depressed and laterally expanded, 

 with peculiar laminations on its edges; while the rostrum of the lower surface 

 of the skull shows well-marked basipterygoid facets for the articulation of the 

 pterygoid bones. In the skeleton of the body the metacoracoid is much longer 

 and narrower than that of the flamingoes, and is also much less firmly articulated 

 to the breast-bone. The plumage is characterised by its dense and compact nature, 

 and the facility with which water is thrown off from its surface. In the wings 

 there are always ten primary quills, but the number of tail-feathers is liable to 

 variation. All the members of the order moult annually in the 

 autumn, and the quills of the wings are generally shed so 

 rapidly as to incapacitate the birds for flight for some days. 

 In the true ducks, however, the males change their contour- 

 feathers twice in the year. Although the ducks resemble the 

 flamingoes in laying uniformly-coloured eggs, they differ in that 

 the number in a clutch is large, instead of being generally but 

 a pair ; the eggs themselves are further characterised by their 

 hard and usually very smooth shells. 



The general external appearance of the members of the 

 duck tribe is too well known to need special mention. It may 

 be observed, however, that their build is that best adapted for 

 rapid progress through the water ; the breast and fore-part of 

 the body being broad and rounded, the hinder extremity 

 narrow and tapering, and the legs placed relatively far back. 

 Although it has been attempted to divide the members 



FRONT AND LOWER VIEWS of the order into S6veral distinct families, the whole of them 

 OF THE RIGHT CANNON- are so nearly allied that it seems impossible to do more than 

 BONE OF A DUCK. group the genera of the one family Anatidce under several 

 subfamilies, and even some of these are very difficult of definition. The species 

 of the family, which are probably about one hundred and sixty in number, are 

 distributed all over the globe, although more numerous in the higher latitudes 

 of the Northern Hemisphere than elsewhere. All are thoroughly aquatic in their 

 habits; but while the majority are swimmers, the members of one group are 

 expert divers. As a rule, they associate in flocks of larger or smaller size, and 

 migrate in numbers to the northern portions of their habitat for the breeding- 

 season. They are all birds of strong flight, and when on the wing fly in the 

 well-known chevron -shaped formation, frequently at a great height in the air. 

 Although the majority of the species are more or less omnivorous in their diet, 

 the mergansers subsist exclusively on fish, while the greater part of the food of 

 the geese consists of grass. The group is not a very ancient one, the earliest 

 known forms occurring in the lower beds of the Miocene division of the Tertiary 

 period. 



Spur- winged The African spur-winged geese (Plectropterus), of which there 



Geese. are ^ wo species, take their name from the long spur on each wing, 



which is sharply pointed and attached to the outer side of the wrist-joint ; and as 



they differ in several important points from the other members of the order, they 



constitute a subfamily by themselves, some writers even making them the repre- 



