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 Hable 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 
of the order into several distinct families, the whole of them 

FRONT AND LOWER VIEWS ‘ S . : 
OF THE RIGHT cANNon- are so nearly allied that it seems impossible to do more than 
a cae yaa eroup the genera of the one family Anatide 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 
Grace: are two 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- 
