EGGS AND EGG-COLLECTING. 9 
Moulting has been rendered subject to the law of 
preservation in a remarkable degree, for where birds 
are open to periodical changes of surrounding con- 
ditions which materially affect their existence, they are. 
provided with an extra moult. For example, the Ptar- 
migan’s plumage is pure white for winter snow, and 
brown for summer heather. 
The stoat’s fur undergoes a similar change of colour ; 
and more marvellous still, to pursue the preservation argu- 
ment into the water world, take a common trout, and chase 
him up and down a shallow pool until he has become 
thoroughly scared, and it will be found that wherever he 
rests for a few seconds his colour will change in obedience 
to that of the bed of the stream directly beneath him; so 
much so that I have known one half of a trout very dark 
and the other half very light coloured, correspondingly with 
objects beneath and around him. 
Again, the same high authority points out that “ the 
feathers of young birds are in male and female similar to 
the female parent when she is of a dull colour, but like the 
male when he is dull and the female bright; also, when both 
parents are of a conspicuously bright colour the young take 
a dull colour of their own ””’—for example, Robins. He infers 
that these colours represent those of far distant progenitors ; 
but as safety lies in these modified tints, and preservation 
being Nature’s chief problem, it is more reasonable to suppose 
that Nature lends this means of protection whilst the bird 
is in its most helpless condition, for an evolution that tends 
to increase dangerously conspicuous colours would only 
seem to invite extinction. 
In another place he says “ it deserves especial attention 
that brilliant colours have been transferred much more 
