160 THE STRUCTURE AND LIFE OF BIRDS cuap. 
attributes the change not to a breaking off of the 
edges, but to a peeling of the barbules. However this 
may be, he must surely be right when he maintains 
that inspring there is a rounding off of the ragged 
edges of feathers. The Linnet’s nuptial plumage 
would be but a sorry garb if the dropping away of the 
edges left what remained all ragged. A far more 
remarkable cause of change of colour is the entrance 
of fresh colouring matter into the feather, which can- 
not therefore be an entirely dead thing. This is what 
takes place when the Blackheaded Gull puts on his 
spring head-dress, the colour, according to Gitke, 
appearing first at the edges of the feathers and 
gradually extending till the whole is dyed. In winter 
the breast of the Dunlin is almost white, in spring it 
becomes black, the pigment working its way to every 
part of the feathers through channels as yet un- 
discovered. By a similar process the head of the 
Little Gull changes in spring from white with a dash 
of ashen-gray to black. Asin the Linnet in captivity, 
so in the Herring Gull there takes place a withdrawal 
of pigment, for the head having been gray in winter 
becomes snow-white in spring. In these cases no 
indication of moulting, such as half-grown feathers, is 
ever found. The plumage of the Wood-sandpiper is 
an interesting study, since it supplies an example of 
the influx of fresh colour into the feathers and also of 
the rounding off of ragged edges. Birds in captivity 
sometimes show these changes well. This year the 
Knots at the Zoological Gardens appeared with the 
chestnut-coloured breasts proper to them in spring, 
but whether the change in their case is due to the dull 
