374 NATATORES. MERGUS. 
tarsus. Hind toe reaching to the ground, and furnished 
with a large lobated membrane. 
General form rather long, much depressed or flattened. 
Head more or less crested. 
The members of this genus are distinguished from the 
preceding subfamilies of the Anatide, by the narrowness of 
the bill, as compared with its length, and by the structure 
of its laminated edges, which assume the form of distinct co- 
nical teeth, generally pointing backwards, instead of the 
broad transverse plates or laminz of the other groups. The 
food of the typical species principally consists of fish, for se- 
curing which this modification of bill is admirably adapted. 
The members of this genus swim well, but, from the weight 
and flattened form of their bodies, appear deeply immersed 
in the water; the head, neck, and back being only visible. 
They are also excellent divers, moving or rather flying be- 
neath the surface with great rapidity, and to a great dis- 
tance at a time, and by these submarine flights they capture 
their finny prey. Their flight is strong and swift, and they 
have great endurance on wing; but, from the shortness and 
backward position of the legs, are awkward upon land. They 
are natives of the colder climates, and are found, during the 
summer (or breeding season), in very high latitudes. The 
males, after the sexual connexion, are subject to a partial 
change in the colours of their plumage, similar to that which 
takes place in many species of the subfamily Anatina. The 
labyrinthic part of the trachea (only in the male bird) is 
very large and complicated, and the tube itself varies in 
form and in the number of its enlargements, according to the 
species. The young males bear a strong resemblance to the 
females, till after the second moult. 
