386 THE STRUCTURE AND LIFE OF BIRDS CHAP. 
Among its representatives are the Kingfishers and 
the Nightjars, which thus are near relations of the 
Swifts. The Humming-birds are often put by them- 
selves as a separate Passerine sub-order ; but they are 
still a bone of contention, and it will probably be 
long before they are allowed to settle in a comfortable 
corner. 
As affording a typical instance of difficulty, I 
mention two families, the Piciformes and Coccyges, 
to many representatives of both of which what is, 
perhaps, their most striking characteristic is com- 
mon; they have zygodactyle or yoketoed feet:' How 
are they to be distinguished? The Piciformes—ze. 
the Woodpeckers and their allies—have a _ well- 
marked feather tract on the neck with bare spaces 
on either side, while in our Cuckoo, who represents 
the Coccyges in Britain, the neck is all thickly 
covered with feathers. 
Mr. Mivart’s order, the Limicoliformes, illustrates 
well the difference between the older systems and 
the new. Most of the birds included were formcrly 
put down as Waders because of their mode of life. 
These Waders are now grouped with a number of 
other species which do not wade. Their relationship 
is shown by the fact that they are born with down on 
them and are able almost at once to run; that they 
have a divided feather-tract on the forepart of the 
back; that they have an oil gland tufted with 
feathers. These and other characters cause the in- 
clusion of the Gulls and Terns within the same order 
as the Waders. 
1 See p. 165. 
