Vi FORM AND FUNCTION 155 
Moulting. 
Moulting, as I have already said, is a reptilian 
characteristic, and corresponds to the shedding of 
the horny covering of the scales. It is due to the 
papilla which once more extends into the quill 
and causes the feather to fall off. In the Cassowary 
and Emeu the tip of the new feather extends into 
the base of the old one, which it carries for a time, 
but the two are only connected mechanically. 
They do not, like the nestling down and the feather 
that follows it, make up one organ. Most birds 
moult completely in the summer or autumn. 
Many have a partial moult, at which only small 
feathers are shed, in spring. It is sometimes stated 
that migratory birds have two complete moults, one 
before each migration, but it is probable that none of 
them shed their great quill feathers more than once. 
The Cuckoo’s main moult is believed to be in spring: 
sometimes he has arrived in England before its comple- 
tion. In autumn, after he has left us, the smaller feathers 
are once more changed. Swifts also, it is supposed, 
moult in early spring long before they come to us, 
a slighter moult taking place after their departure. 
Swallows and Martins moult only once—in very 
early spring or even in winter—being distinguished 
by this from the Swifts, which moult twice. With 
most migrants, as with other birds, autumn is the 
great season for donning new feathers. Spring is the 
time when the wedding plumage is put on, and the 
Ruffs, the Golden Plovers, the Dunlins, the Linnets, 
