86 
BIKD-LIFE. 
renewed. For this reason, the Ptarmigan ( Lagopus ) has 
the aforesaid feathers (except the middle tail-feathers) 
always of the same colour, though, in other respects, the 
two dresses are quite different. The throwing off and 
the discoloration of the feathers may be, to a certain 
extent, regarded as the completion of the moult. With 
many birds the new feathers have at first white or gray 
edges: these, in the course of the winter, become worn 
away, and then reveal what they have hitherto hidden, 
viz. the often quite differently-coloured centre of the 
feathers. At the same time, however, the colours appear 
brighter, though from what cause we are, as yet, 
ignorant. This peculiar intensifying of colour has lately 
been the cause of much word warfare, some naturalists 
regarding it as the cause of changes in colour of plumage 
in certain birds only, whilst others hold a contrary 
opinion. In truth, it would appear as though this action 
or influence had till now been under-valued. It was 
thought unreasonable to suppose that a perfect feather 
could continue to draw nourishment from the body; 
thus the occurrence of increased action could not be 
explained. For this reason, alone, it would seem that 
the argument is based upon wrong premises. If feathers, 
as it has been assumed, receive no further nourishment 
after having reached maturity, they surely would never 
receive a sudden increase of brilliancy in their colouring. 
It is indisputable that the colouring of a feather depends 
principally upon the actual construction of its individual 
parts, it can, therefore, not be supposed that the wearing 
out of this very conformation should be the sole cause of 
the future brilliancy of the feather! It is evident that in 
this case there must be some other agency at work, and, 
this being so, the only thing we can suggest is, that a 
